Red Hat Enterprise Linux 8
Developing C and C++ applications in RHEL 8
Setting up a developer workstation, and developing and debugging C and C++
applications in Red Hat Enterprise Linux 8
Last Updated: 2024-07-08
Red Hat Enterprise Linux 8 Developing C and C++ applications in RHEL 8
Setting up a developer workstation, and developing and debugging C and C++ applications in Red
Hat Enterprise Linux 8
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Abstract
Use the different features and utilities available in Red Hat Enterprise Linux 8 to develop and debug
C and C++ applications.
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Table of Contents
PROVIDING FEEDBACK ON RED HAT DOCUMENTATION
CHAPTER 1. SETTING UP A DEVELOPMENT WORKSTATION
1.1. PREREQUISITES
1.2. ENABLING DEBUG AND SOURCE REPOSITORIES
1.3. SETTING UP TO MANAGE APPLICATION VERSIONS
1.4. SETTING UP TO DEVELOP APPLICATIONS USING C AND C++
1.5. SETTING UP TO DEBUG APPLICATIONS
1.6. SETTING UP TO MEASURE PERFORMANCE OF APPLICATIONS
CHAPTER 2. CREATING C OR C++ APPLICATIONS
2.1. BUILDING CODE WITH GCC
2.1.1. Relationship between code forms
2.1.2. Compiling source files to object code
2.1.3. Enabling debugging of C and C++ applications with GCC
2.1.4. Code optimization with GCC
2.1.5. Options for hardening code with GCC
2.1.6. Linking code to create executable files
2.1.7. Example: Building a C program with GCC (compiling and linking in one step)
2.1.8. Example: Building a C program with GCC (compiling and linking in two steps)
2.1.9. Example: Building a C++ program with GCC (compiling and linking in one step)
2.1.10. Example: Building a C++ program with GCC (compiling and linking in two steps)
2.2. USING LIBRARIES WITH GCC
2.2.1. Library naming conventions
2.2.2. Static and dynamic linking
2.2.3. Using a library with GCC
2.2.4. Using a static library with GCC
2.2.5. Using a dynamic library with GCC
2.2.6. Using both static and dynamic libraries with GCC
2.3. CREATING LIBRARIES WITH GCC
2.3.1. Library naming conventions
2.3.2. The soname mechanism
2.3.3. Creating dynamic libraries with GCC
2.3.4. Creating static libraries with GCC and ar
2.4. MANAGING MORE CODE WITH MAKE
2.4.1. GNU make and Makefile overview
2.4.2. Example: Building a C program using a Makefile
2.4.3. Documentation resources for make
2.5. CHANGES IN TOOLCHAIN SINCE RHEL 7
2.5.1. Changes in GCC in RHEL 8
2.5.2. Security enhancements in GCC in RHEL 8
2.5.3. Compatibility-breaking changes in GCC in RHEL 8
C++ ABI change in std::string and std::list
GCC no longer builds Ada, Go, and Objective C/C++ code
CHAPTER 3. DEBUGGING APPLICATIONS
3.1. ENABLING DEBUGGING WITH DEBUGGING INFORMATION
3.1.1. Debugging information
3.1.2. Enabling debugging of C and C++ applications with GCC
3.1.3. Debuginfo and debugsource packages
3.1.4. Getting debuginfo packages for an application or library using GDB
3.1.5. Getting debuginfo packages for an application or library manually
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3.2. INSPECTING APPLICATION INTERNAL STATE WITH GDB
3.2.1. GNU debugger (GDB)
3.2.2. Attaching GDB to a process
3.2.3. Stepping through program code with GDB
3.2.4. Showing program internal values with GDB
3.2.5. Using GDB breakpoints to stop execution at defined code locations
3.2.6. Using GDB watchpoints to stop execution on data access and changes
3.2.7. Debugging forking or threaded programs with GDB
3.3. RECORDING APPLICATION INTERACTIONS
3.3.1. Tools useful for recording application interactions
3.3.2. Monitoring an application’s system calls with strace
3.3.3. Monitoring application’s library function calls with ltrace
3.3.4. Monitoring application’s system calls with SystemTap
3.3.5. Using GDB to intercept application system calls
3.3.6. Using GDB to intercept handling of signals by applications
3.4. DEBUGGING A CRASHED APPLICATION
3.4.1. Core dumps: what they are and how to use them
3.4.2. Recording application crashes with core dumps
3.4.3. Inspecting application crash states with core dumps
3.4.4. Creating and accessing a core dump with coredumpctl
3.4.5. Dumping process memory with gcore
3.4.6. Dumping protected process memory with GDB
3.5. COMPATIBILITY-BREAKING CHANGES IN GDB
GDBserver now starts inferiors with shell
gcj support removed
New syntax for symbol dumping maintenance commands
Thread numbers are no longer global
Memory for value contents can be limited
Sun version of stabs format no longer supported
Sysroot handling changes
HISTSIZE no longer controls GDB command history size
Completion limiting added
HP-UX XDB compatibility mode removed
Handling signals for threads
Breakpoint modes always-inserted off and auto merged
remotebaud commands no longer supported
3.6. DEBUGGING APPLICATIONS IN CONTAINERS
CHAPTER 4. ADDITIONAL TOOLSETS FOR DEVELOPMENT
4.1. USING GCC TOOLSET
4.1.1. What is GCC Toolset
4.1.2. Installing GCC Toolset
4.1.3. Installing individual packages from GCC Toolset
4.1.4. Uninstalling GCC Toolset
4.1.5. Running a tool from GCC Toolset
4.1.6. Running a shell session with GCC Toolset
4.1.7. Additional resources
4.2. GCC TOOLSET 9
4.2.1. Tools and versions provided by GCC Toolset 9
4.2.2. C++ compatibility in GCC Toolset 9
4.2.3. Specifics of GCC in GCC Toolset 9
4.2.4. Specifics of binutils in GCC Toolset 9
4.3. GCC TOOLSET 10
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4.3.1. Tools and versions provided by GCC Toolset 10
4.3.2. C++ compatibility in GCC Toolset 10
4.3.3. Specifics of GCC in GCC Toolset 10
4.3.4. Specifics of binutils in GCC Toolset 10
4.4. GCC TOOLSET 11
4.4.1. Tools and versions provided by GCC Toolset 11
4.4.2. C++ compatibility in GCC Toolset 11
4.4.3. Specifics of GCC in GCC Toolset 11
4.4.4. Specifics of binutils in GCC Toolset 11
4.5. GCC TOOLSET 12
4.5.1. Tools and versions provided by GCC Toolset 12
4.5.2. C++ compatibility in GCC Toolset 12
4.5.3. Specifics of GCC in GCC Toolset 12
4.5.4. Specifics of binutils in GCC Toolset 12
4.5.5. Specifics of annobin in GCC Toolset 12
4.6. GCC TOOLSET 13
4.6.1. Tools and versions provided by GCC Toolset 13
4.6.2. C++ compatibility in GCC Toolset 13
4.6.3. Specifics of GCC in GCC Toolset 13
4.6.4. Specifics of binutils in GCC Toolset 13
4.6.5. Specifics of annobin in GCC Toolset 13
4.7. USING THE GCC TOOLSET CONTAINER IMAGE
4.7.1. GCC Toolset container image contents
4.7.2. Accessing and running the GCC Toolset container image
4.7.3. Example: Using the GCC Toolset 13 Toolchain container image
4.8. COMPILER TOOLSETS
4.9. THE ANNOBIN PROJECT
4.9.1. Using the annobin plugin
4.9.1.1. Enabling the annobin plugin
4.9.1.2. Passing options to the annobin plugin
4.9.2. Using the annocheck program
4.9.2.1. Using annocheck to examine files
4.9.2.2. Using annocheck to examine directories
4.9.2.3. Using annocheck to examine RPM packages
4.9.2.4. Using annocheck extra tools
4.9.2.4.1. Enabling the built-by tool
4.9.2.4.2. Enabling the notes tool
4.9.2.4.3. Enabling the section-size tool
4.9.2.4.4. Hardening checker basics
4.9.2.4.4.1. Hardening checker options
4.9.2.4.4.2. Disabling the hardening checker
4.9.3. Removing redundant annobin notes
4.9.4. Specifics of annobin in GCC Toolset 12
CHAPTER 5. SUPPLEMENTARY TOPICS
5.1. COMPATIBILITY-BREAKING CHANGES IN COMPILERS AND DEVELOPMENT TOOLS
librtkaio removed
Sun RPC and NIS interfaces removed from glibc
The nosegneg libraries for 32-bit Xen have been removed
make new operator != causes a different interpretation of certain existing makefile syntax
Valgrind library for MPI debugging support removed
Development headers and static libraries removed from valgrind-devel
5.2. OPTIONS FOR RUNNING A RHEL 6 OR 7 APPLICATION ON RHEL 8
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PROVIDING FEEDBACK ON RED HAT DOCUMENTATION
We appreciate your feedback on our documentation. Let us know how we can improve it.
Submitting feedback through Jira (account required)
1. Log in to the Jira website.
2. Click Create in the top navigation bar.
3. Enter a descriptive title in the Summary field.
4. Enter your suggestion for improvement in the Description field. Include links to the relevant
parts of the documentation.
5. Click Create at the bottom of the dialogue.
PROVIDING FEEDBACK ON RED HAT DOCUMENTATION
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CHAPTER 1. SETTING UP A DEVELOPMENT WORKSTATION
Red Hat Enterprise Linux 8 supports development of custom applications. To allow developers to do so,
the system must be set up with the required tools and utilities. This chapter lists the most common use
cases for development and the items to install.
1.1. PREREQUISITES
The system must be installed, including a graphical environment, and subscribed.
1.2. ENABLING DEBUG AND SOURCE REPOSITORIES
A standard installation of Red Hat Enterprise Linux does not enable the debug and source repositories.
These repositories contain information needed to debug the system components and measure their
performance.
Procedure
Enable the source and debug information package channels:
# subscription-manager repos --enable rhel-8-for-$(uname -i)-baseos-debug-rpms
# subscription-manager repos --enable rhel-8-for-$(uname -i)-baseos-source-rpms
# subscription-manager repos --enable rhel-8-for-$(uname -i)-appstream-debug-rpms
# subscription-manager repos --enable rhel-8-for-$(uname -i)-appstream-source-rpms
The $(uname -i) part is automatically replaced with a matching value for architecture of your
system:
Architecture name Value
64-bit Intel and AMD x86_64
64-bit ARM aarch64
IBM POWER ppc64le
64-bit IBM Z s390x
1.3. SETTING UP TO MANAGE APPLICATION VERSIONS
Effective version control is essential to all multi-developer projects. Red Hat Enterprise Linux is shipped
with Git, a distributed version control system.
Procedure
1. Install the git package:
# yum install git
2. Optional: Set the full name and email address associated with your Git commits:
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$ git config --global user.name "Full Name"
$ git config --global user.email "email@example.com"
Replace Full Name and email@example.com with your actual name and email address.
3. Optional: To change the default text editor started by Git, set value of the core.editor
configuration option:
$ git config --global core.editor command
Replace command with the command to be used to start the selected text editor.
Additional resources
Linux manual pages for Git and tutorials:
$ man git
$ man gittutorial
$ man gittutorial-2
Note that many Git commands have their own manual pages. As an example see git-commit(1).
Git User’s Manual — HTML documentation for Git is located at /usr/share/doc/git/user-
manual.html.
Pro Git — The online version of the Pro Git book provides a detailed description of Git, its
concepts, and its usage.
Reference — Online version of the Linux manual pages for Git
1.4. SETTING UP TO DEVELOP APPLICATIONS USING C AND C++
Red Hat Enterprise Linux includes tools for creating C and C++ applications.
Prerequisites
The debug and source repositories must be enabled.
Procedure
1. Install the Development Tools package group including GNU Compiler Collection (GCC), GNU
Debugger (GDB), and other development tools:
# yum group install "Development Tools"
2. Install the LLVM-based toolchain including the clang compiler and lldb debugger:
# yum install llvm-toolset
3. Optional: For Fortran dependencies, install the GNU Fortran compiler:
# yum install gcc-gfortran
CHAPTER 1. SETTING UP A DEVELOPMENT WORKSTATION
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1.5. SETTING UP TO DEBUG APPLICATIONS
Red Hat Enterprise Linux offers multiple debugging and instrumentation tools to analyze and
troubleshoot internal application behavior.
Prerequisites
The debug and source repositories must be enabled.
Procedure
1. Install the tools useful for debugging:
# yum install gdb valgrind systemtap ltrace strace
2. Install the yum-utils package in order to use the debuginfo-install tool:
# yum install yum-utils
3. Run a SystemTap helper script for setting up the environment.
# stap-prep
Note that stap-prep installs packages relevant to the currently running kernel, which might not
be the same as the actually installed kernel(s). To ensure stap-prep installs the correct kernel-
debuginfo and kernel-headers packages, double-check the current kernel version by using the
uname -r command and reboot your system if necessary.
4. Make sure SELinux policies allow the relevant applications to run not only normally, but in the
debugging situations, too. For more information, see Using SELinux.
Additional resources
Section 3.1, “Enabling Debugging with Debugging Information”
1.6. SETTING UP TO MEASURE PERFORMANCE OF APPLICATIONS
Red Hat Enterprise Linux includes several applications that can help a developer identify the causes of
application performance loss.
Prerequisites
The debug and source repositories must be enabled.
Procedure
1. Install the tools for performance measurement:
# yum install perf papi pcp-zeroconf valgrind strace sysstat systemtap
2. Run a SystemTap helper script for setting up the environment.
# stap-prep
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Note that stap-prep installs packages relevant to the currently running kernel, which might not
be the same as the actually installed kernel(s). To ensure stap-prep installs the correct kernel-
debuginfo and kernel-headers packages, double-check the current kernel version by using the
uname -r command and reboot your system if necessary.
3. Enable and start the Performance Co-Pilot (PCP) collector service:
# systemctl enable pmcd && systemctl start pmcd
CHAPTER 1. SETTING UP A DEVELOPMENT WORKSTATION
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CHAPTER 2. CREATING C OR C++ APPLICATIONS
2.1. BUILDING CODE WITH GCC
Learn about situations where source code must be transformed into executable code.
2.1.1. Relationship between code forms
Prerequisites
Understanding the concepts of compiling and linking
Possible code forms
The C and C++ languages have three forms of code:
Source code written in the C or C++ language, present as plain text files.
The files typically use extensions such as .c, .cc, .cpp, .h, .hpp, .i, .inc. For a complete list of
supported extensions and their interpretation, see the gcc manual pages:
$ man gcc
Object code, created by compiling the source code with a compiler. This is an intermediate
form.
The object code files use the .o extension.
Executable code, created by linking object code with a linker.
Linux application executable files do not use any file name extension. Shared object (library)
executable files use the .so file name extension.
NOTE
Library archive files for static linking also exist. This is a variant of object code that uses
the .a file name extension. Static linking is not recommended. See Section 2.2.2, “Static
and dynamic linking”.
Handling of code forms in GCC
Producing executable code from source code is performed in two steps, which require different
applications or tools. GCC can be used as an intelligent driver for both compilers and linkers. This allows
you to use a single gcc command for any of the required actions (compiling and linking). GCC
automatically selects the actions and their sequence:
1. Source files are compiled to object files.
2. Object files and libraries are linked (including the previously compiled sources).
It is possible to run GCC so that it performs only compiling, only linking, or both compiling and linking in
a single step. This is determined by the types of inputs and requested type of output(s).
Because larger projects require a build system which usually runs GCC separately for each action, it is
better to always consider compilation and linking as two distinct actions, even if GCC can perform both
at once.
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Additional resources
Section 2.1.2, “Compiling source files to object code”
Section 2.1.6, “Linking code to create executable files”
Example: Building a C program with GCC (compiling and linking in one step)
Example: Building a C program with GCC (compiling and linking in two steps)
2.1.2. Compiling source files to object code
To create object code files from source files and not an executable file immediately, GCC must be
instructed to create only object code files as its output. This action represents the basic operation of the
build process for larger projects.
Prerequisites
C or C++ source code file(s)
GCC installed on the system
Procedure
1. Change to the directory containing the source code file(s).
2. Run gcc with the -c option:
$ gcc -c source.c another_source.c
Object files are created, with their file names reflecting the original source code files: source.c
results in source.o.
NOTE
With C++ source code, replace the gcc command with g++ for convenient
handling of C++ Standard Library dependencies.
Additional resources
Section 2.1.5, “Options for hardening code with GCC”
Section 2.1.4, “Code optimization with GCC”
Section 2.1.7, “Example: Building a C program with GCC (compiling and linking in one step)”
2.1.3. Enabling debugging of C and C++ applications with GCC
Because debugging information is large, it is not included in executable files by default. To enable
debugging of your C and C++ applications with it, you must explicitly instruct the compiler to create it.
To enable creation of debugging information with GCC when compiling and linking code, use the -g
option:
$ gcc ... -g ...
CHAPTER 2. CREATING C OR C++ APPLICATIONS
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Optimizations performed by the compiler and linker can result in executable code which is hard
to relate to the original source code: variables may be optimized out, loops unrolled, operations
merged into the surrounding ones, and so on. This affects debugging negatively. For improved
debugging experience, consider setting the optimization with the -Og option. However,
changing the optimization level changes the executable code and may change the actual
behaviour including removing some bugs.
To also include macro definitions in the debug information, use the -g3 option instead of -g.
The -fcompare-debug GCC option tests code compiled by GCC with debug information and
without debug information. The test passes if the resulting two binary files are identical. This
test ensures that executable code is not affected by any debugging options, which further
ensures that there are no hidden bugs in the debug code. Note that using the -fcompare-debug
option significantly increases compilation time. See the GCC manual page for details about this
option.
Additional resources
Section 3.1, “Enabling Debugging with Debugging Information”
Using the GNU Compiler Collection (GCC) — Options for Debugging Your Program
Debugging with GDB — Debugging Information in Separate Files
The GCC manual page:
$ man gcc
2.1.4. Code optimization with GCC
A single program can be transformed into more than one sequence of machine instructions. You can
achieve a more optimal result if you allocate more resources to analyzing the code during compilation.
With GCC, you can set the optimization level using the -Olevel option. This option accepts a set of
values in place of the level.
Level Description
0 Optimize for compilation speed - no code optimization (default).
1, 2, 3 Optimize to increase code execution speed (the larger the number, the greater the speed).
s Optimize for file size.
fast Same as a level 3 setting, plus fast disregards strict standards compliance to allow for
additional optimizations.
g Optimize for debugging experience.
For release builds, use the optimization option -O2.
During development, the -Og option is useful for debugging the program or library in some situations.
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During development, the -Og option is useful for debugging the program or library in some situations.
Because some bugs manifest only with certain optimization levels, test the program or library with the
release optimization level.
GCC offers a large number of options to enable individual optimizations. For more information, see the
following Additional resources.
Additional resources
Using GNU Compiler Collection — Options That Control Optimization
Linux manual page for GCC:
$ man gcc
2.1.5. Options for hardening code with GCC
When the compiler transforms source code to object code, it can add various checks to prevent
commonly exploited situations and increase security. Choosing the right set of compiler options can
help produce more secure programs and libraries, without having to change the source code.
Release version options
The following list of options is the recommended minimum for developers targeting Red Hat
Enterprise Linux:
$ gcc ... -O2 -g -Wall -Wl,-z,now,-z,relro -fstack-protector-strong -fstack-clash-protection -
D_FORTIFY_SOURCE=2 ...
For programs, add the -fPIE and -pie Position Independent Executable options.
For dynamically linked libraries, the mandatory -fPIC (Position Independent Code) option
indirectly increases security.
Development options
Use the following options to detect security flaws during development. Use these options in conjunction
with the options for the release version:
$ gcc ... -Walloc-zero -Walloca-larger-than -Wextra -Wformat-security -Wvla-larger-than ...
Additional resources
Defensive Coding Guide
Memory Error Detection Using GCC — Red Hat Developers Blog post
2.1.6. Linking code to create executable files
Linking is the final step when building a C or C++ application. Linking combines all object files and
libraries into an executable file.
Prerequisites
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One or more object file(s)
GCC must be installed on the system
Procedure
1. Change to the directory containing the object code file(s).
2. Run gcc:
$ gcc ... objfile.o another_object.o ... -o executable-file
An executable file named executable-file is created from the supplied object files and libraries.
To link additional libraries, add the required options after the list of object files. For more
information, see Section 2.2, “Using Libraries with GCC” .
NOTE
With C++ source code, replace the gcc command with g++ for convenient
handling of C++ Standard Library dependencies.
Additional resources
Section 2.1.7, “Example: Building a C program with GCC (compiling and linking in one step)”
Section 2.2.2, “Static and dynamic linking”
2.1.7. Example: Building a C program with GCC (compiling and linking in one step)
This example shows the exact steps to build a simple sample C program.
In this example, compiling and linking the code is done in one step.
Prerequisites
You must understand how to use GCC.
Procedure
1. Create a directory hello-c and change to it:
$ mkdir hello-c
$ cd hello-c
2. Create file hello.c with the following contents:
#include <stdio.h>
int main() {
printf("Hello, World!\n");
return 0;
}
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3. Compile and link the code with GCC:
$ gcc hello.c -o helloworld
This compiles the code, creates the object file hello.o, and links the executable file helloworld
from the object file.
4. Run the resulting executable file:
$ ./helloworld
Hello, World!
Additional resources
Section 2.4.2, “Example: Building a C program using a Makefile”
2.1.8. Example: Building a C program with GCC (compiling and linking in two steps)
This example shows the exact steps to build a simple sample C program.
In this example, compiling and linking the code are two separate steps.
Prerequisites
You must understand how to use GCC.
Procedure
1. Create a directory hello-c and change to it:
$ mkdir hello-c
$ cd hello-c
2. Create file hello.c with the following contents:
3. Compile the code with GCC:
$ gcc -c hello.c
The object file hello.o is created.
4. Link an executable file helloworld from the object file:
$ gcc hello.o -o helloworld
5. Run the resulting executable file:
#include <stdio.h>
int main() {
printf("Hello, World!\n");
return 0;
}
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$ ./helloworld
Hello, World!
Additional resources
Section 2.4.2, “Example: Building a C program using a Makefile”
2.1.9. Example: Building a C++ program with GCC (compiling and linking in one step)
This example shows the exact steps to build a sample minimal C++ program.
In this example, compiling and linking the code is done in one step.
Prerequisites
You must understand the difference between gcc and g++.
Procedure
1. Create a directory hello-cpp and change to it:
$ mkdir hello-cpp
$ cd hello-cpp
2. Create file hello.cpp with the following contents:
3. Compile and link the code with g++:
$ g++ hello.cpp -o helloworld
This compiles the code, creates the object file hello.o, and links the executable file helloworld
from the object file.
4. Run the resulting executable file:
$ ./helloworld
Hello, World!
2.1.10. Example: Building a C++ program with GCC (compiling and linking in two
steps)
This example shows the exact steps to build a sample minimal C++ program.
In this example, compiling and linking the code are two separate steps.
#include <iostream>
int main() {
std::cout << "Hello, World!\n";
return 0;
}
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Prerequisites
You must understand the difference between gcc and g++.
Procedure
1. Create a directory hello-cpp and change to it:
$ mkdir hello-cpp
$ cd hello-cpp
2. Create file hello.cpp with the following contents:
3. Compile the code with g++:
$ g++ -c hello.cpp
The object file hello.o is created.
4. Link an executable file helloworld from the object file:
$ g++ hello.o -o helloworld
5. Run the resulting executable file:
$ ./helloworld
Hello, World!
2.2. USING LIBRARIES WITH GCC
Learn about using libraries in code.
2.2.1. Library naming conventions
A special file name convention is used for libraries: a library known as foo is expected to exist as file
libfoo.so or libfoo.a. This convention is automatically understood by the linking input options of GCC,
but not by the output options:
When linking against the library, the library can be specified only by its name foo with the -l
option as -lfoo:
$ gcc ... -lfoo ...
When creating the library, the full file name libfoo.so or libfoo.a must be specified.
#include <iostream>
int main() {
std::cout << "Hello, World!\n";
return 0;
}
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Additional resources
Section 2.3.2, “The soname mechanism”
2.2.2. Static and dynamic linking
Developers have a choice of using static or dynamic linking when building applications with fully
compiled languages. It is important to understand the differences between static and dynamic linking,
particularly in the context using the C and C++ languages on Red Hat Enterprise Linux. To summarize,
Red Hat discourages the use of static linking in applications for Red Hat Enterprise Linux.
Comparison of static and dynamic linking
Static linking makes libraries part of the resulting executable file. Dynamic linking keeps these libraries
as separate files.
Dynamic and static linking can be compared in a number of ways:
Resource use
Static linking results in larger executable files which contain more code. This additional code coming
from libraries cannot be shared across multiple programs on the system, increasing file system usage
and memory usage at run time. Multiple processes running the same statically linked program will still
share the code.
On the other hand, static applications need fewer run-time relocations, leading to reduced startup
time, and require less private resident set size (RSS) memory. Generated code for static linking can
be more efficient than for dynamic linking due to the overhead introduced by position-independent
code (PIC).
Security
Dynamically linked libraries which provide ABI compatibility can be updated without changing the
executable files depending on these libraries. This is especially important for libraries provided by
Red Hat as part of Red Hat Enterprise Linux, where Red Hat provides security updates. Static linking
against any such libraries is strongly discouraged.
Compatibility
Static linking appears to provide executable files independent of the versions of libraries provided by
the operating system. However, most libraries depend on other libraries. With static linking, this
dependency becomes inflexible and as a result, both forward and backward compatibility is lost.
Static linking is guaranteed to work only on the system where the executable file was built.
WARNING
Applications linking statically libraries from the GNU C library (glibc) still require
glibc to be present on the system as a dynamic library. Furthermore, the
dynamic library variant of glibc available at the application’s run time must be a
bitwise identical version to that present while linking the application. As a result,
static linking is guaranteed to work only on the system where the executable file
was built.
Support coverage
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Most static libraries provided by Red Hat are in the CodeReady Linux Builder channel and not
supported by Red Hat.
Functionality
Some libraries, notably the GNU C Library (glibc), offer reduced functionality when linked statically.
For example, when statically linked, glibc does not support threads and any form of calls to the
dlopen() function in the same program.
As a result of the listed disadvantages, static linking should be avoided at all costs, particularly for whole
applications and the glibc and libstdc++ libraries.
Cases for static linking
Static linking might be a reasonable choice in some cases, such as:
Using a library which is not enabled for dynamic linking.
Fully static linking can be required for running code in an empty chroot environment or
container. However, static linking using the glibc-static package is not supported by Red Hat.
Additional resources
Red Hat Enterprise Linux 8: Application Compatibility GUIDE
Description of the The CodeReady Linux Builder repository in the Package manifest
2.2.3. Using a library with GCC
A library is a package of code which can be reused in your program. A C or C++ library consists of two
parts:
The library code
Header files
Compiling code that uses a library
The header files describe the interface of the library: the functions and variables available in the library.
Information from the header files is needed for compiling the code.
Typically, header files of a library will be placed in a different directory than your application’s code. To
tell GCC where the header files are, use the -I option:
$ gcc ... -Iinclude_path ...
Replace include_path with the actual path to the header file directory.
The -I option can be used multiple times to add multiple directories with header files. When looking for a
header file, these directories are searched in the order of their appearance in the -I options.
Linking code that uses a library
When linking the executable file, both the object code of your application and the binary code of the
library must be available. The code for static and dynamic libraries is present in different forms:
Static libraries are available as archive files. They contain a group of object files. The archive file
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Static libraries are available as archive files. They contain a group of object files. The archive file
has a file name extension .a.
Dynamic libraries are available as shared objects. They are a form of an executable file. A shared
object has a file name extension .so.
To tell GCC where the archives or shared object files of a library are, use the -L option:
$ gcc ... -Llibrary_path -lfoo ...
Replace library_path with the actual path to the library directory.
The -L option can be used multiple times to add multiple directories. When looking for a library, these
directories are searched in the order of their -L options.
The order of options matters: GCC cannot link against a library foo unless it knows the directory with
this library. Therefore, use the -L options to specify library directories before using the -l options for
linking against libraries.
Compiling and linking code which uses a library in one step
When the situation allows the code to be compiled and linked in one gcc command, use the options for
both situations mentioned above at once.
Additional resources
Using the GNU Compiler Collection (GCC) — Options for Directory Search
Using the GNU Compiler Collection (GCC) — Options for Linking
2.2.4. Using a static library with GCC
Static libraries are available as archives containing object files. After linking, they become part of the
resulting executable file.
NOTE
Red Hat discourages use of static linking for security reasons. See Section 2.2.2, “Static
and dynamic linking”. Use static linking only when necessary, especially against libraries
provided by Red Hat.
Prerequisites
GCC must be installed on your system.
You must understand static and dynamic linking.
You have a set of source or object files forming a valid program, requiring some static library
foo and no other libraries.
The foo library is available as a file libfoo.a, and no file libfoo.so is provided for dynamic linking.
NOTE
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NOTE
Most libraries which are part of Red Hat Enterprise Linux are supported for dynamic
linking only. The steps below only work for libraries which are not enabled for dynamic
linking. See Section 2.2.2, “Static and dynamic linking”.
Procedure
To link a program from source and object files, adding a statically linked library foo, which is to be found
as a file libfoo.a:
1. Change to the directory containing your code.
2. Compile the program source files with headers of the foo library:
$ gcc ... -Iheader_path -c ...
Replace header_path with a path to a directory containing the header files for the foo library.
3. Link the program with the foo library:
$ gcc ... -Llibrary_path -lfoo ...
Replace library_path with a path to a directory containing the file libfoo.a.
4. To run the program later, simply:
$ ./program
WARNING
The -static GCC option related to static linking forbids all dynamic linking. Instead,
use the -Wl,-Bstatic and -Wl,-Bdynamic options to control linker behavior more
precisely. See Section 2.2.6, “Using both static and dynamic libraries with GCC” .
2.2.5. Using a dynamic library with GCC
Dynamic libraries are available as standalone executable files, required at both linking time and run time.
They stay independent of your application’s executable file.
Prerequisites
GCC must be installed on the system.
A set of source or object files forming a valid program, requiring some dynamic library foo and
no other libraries.
The foo library must be available as a file libfoo.so.
Linking a program against a dynamic library
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To link a program against a dynamic library foo:
$ gcc ... -Llibrary_path -lfoo ...
When a program is linked against a dynamic library, the resulting program must always load the library at
run time. There are two options for locating the library:
Using a rpath value stored in the executable file itself
Using the LD_LIBRARY_PATH variable at run time
Using a rpath Value Stored in the Executable File
The rpath is a special value saved as a part of an executable file when it is being linked. Later, when the
program is loaded from its executable file, the runtime linker will use the rpath value to locate the library
files.
While linking with GCC, to store the path library_path as rpath:
$ gcc ... -Llibrary_path -lfoo -Wl,-rpath=library_path ...
The path library_path must point to a directory containing the file libfoo.so.
IMPORTANT
Do not add a space after the comma in the -Wl,-rpath= option.
To run the program later:
$ ./program
Using the LD_LIBRARY_PATH environment variable
If no rpath is found in the program’s executable file, the runtime linker will use the LD_LIBRARY_PATH
environment variable. The value of this variable must be changed for each program. This value should
represent the path where the shared library objects are located.
To run the program without rpath set, with libraries present in path library_path:
$ export LD_LIBRARY_PATH=library_path:$LD_LIBRARY_PATH
$ ./program
Leaving out the rpath value offers flexibility, but requires setting the LD_LIBRARY_PATH variable
every time the program is to run.
Placing the Library into the Default Directories
The runtime linker configuration specifies a number of directories as a default location of dynamic
library files. To use this default behaviour, copy your library to the appropriate directory.
A full description of the dynamic linker behavior is out of scope of this document. For more information,
see the following resources:
Linux manual pages for the dynamic linker:
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$ man ld.so
Contents of the /etc/ld.so.conf configuration file:
$ cat /etc/ld.so.conf
Report of the libraries recognized by the dynamic linker without additional configuration, which
includes the directories:
$ ldconfig -v
2.2.6. Using both static and dynamic libraries with GCC
Sometimes it is required to link some libraries statically and some dynamically. This situation brings some
challenges.
Prerequisites
Understanding static and dynamic linking
Introduction
gcc recognizes both dynamic and static libraries. When the -lfoo option is encountered, gcc will first
attempt to locate a shared object (a .so file) containing a dynamically linked version of the foo library,
and then look for the archive file (.a) containing a static version of the library. Thus, the following
situations can result from this search:
Only the shared object is found, and gcc links against it dynamically.
Only the archive is found, and gcc links against it statically.
Both the shared object and archive are found, and by default, gcc selects dynamic linking
against the shared object.
Neither shared object nor archive is found, and linking fails.
Because of these rules, the best way to select the static or dynamic version of a library for linking is
having only that version found by gcc. This can be controlled to some extent by using or leaving out
directories containing the library versions, when specifying the -Lpath options.
Additionally, because dynamic linking is the default, the only situation where linking must be explicitly
specified is when a library with both versions present should be linked statically. There are two possible
resolutions:
Specifying the static libraries by file path instead of the -l option
Using the -Wl option to pass options to the linker
Specifying the static libraries by file
Usually, gcc is instructed to link against the foo library with the -lfoo option. However, it is possible to
specify the full path to file libfoo.a containing the library instead:
$ gcc ... path/to/libfoo.a ...
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From the file extension .a, gcc will understand that this is a library to link with the program. However,
specifying the full path to the library file is a less flexible method.
Using the -Wl option
The gcc option -Wl is a special option for passing options to the underlying linker. Syntax of this option
differs from the other gcc options. The -Wl option is followed by a comma-separated list of linker
options, while other gcc options require space-separated list of options.
The ld linker used by gcc offers the options -Bstatic and -Bdynamic to specify whether libraries
following this option should be linked statically or dynamically, respectively. After passing -Bstatic and a
library to the linker, the default dynamic linking behaviour must be restored manually for the following
libraries to be linked dynamically with the -Bdynamic option.
To link a program, link library first statically (libfirst.a) and second dynamically (libsecond.so):
$ gcc ... -Wl,-Bstatic -lfirst -Wl,-Bdynamic -lsecond ...
NOTE
gcc can be configured to use linkers other than the default ld.
Additional resources
Using the GNU Compiler Collection (GCC) — 3.14 Options for Linking
Documentation for binutils 2.27 — 2.1 Command Line Options
2.3. CREATING LIBRARIES WITH GCC
Learn about the steps to creating libraries and the necessary concepts used by the Linux operating
system for libraries.
2.3.1. Library naming conventions
A special file name convention is used for libraries: a library known as foo is expected to exist as file
libfoo.so or libfoo.a. This convention is automatically understood by the linking input options of GCC,
but not by the output options:
When linking against the library, the library can be specified only by its name foo with the -l
option as -lfoo:
$ gcc ... -lfoo ...
When creating the library, the full file name libfoo.so or libfoo.a must be specified.
Additional resources
Section 2.3.2, “The soname mechanism”
2.3.2. The soname mechanism
Dynamically loaded libraries (shared objects) use a mechanism called soname to manage multiple
compatible versions of a library.
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Prerequisites
You must understand dynamic linking and libraries.
You must understand the concept of ABI compatibility.
You must understand library naming conventions.
You must understand symbolic links.
Problem introduction
A dynamically loaded library (shared object) exists as an independent executable file. This makes it
possible to update the library without updating the applications that depend on it. However, the
following problems arise with this concept:
Identification of the actual version of the library
Need for multiple versions of the same library present
Signalling ABI compatibility of each of the multiple versions
The soname mechanism
To resolve this, Linux uses a mechanism called soname.
A foo library version X.Y is ABI-compatible with other versions with the same value of X in a version
number. Minor changes preserving compatibility increase the number Y. Major changes that break
compatibility increase the number X.
The actual foo library version X.Y exists as a file libfoo.so.x.y. Inside the library file, a soname is recorded
with value libfoo.so.x to signal the compatibility.
When applications are built, the linker looks for the library by searching for the file libfoo.so. A symbolic
link with this name must exist, pointing to the actual library file. The linker then reads the soname from
the library file and records it into the application executable file. Finally, the linker creates the application
that declares dependency on the library using the soname, not a name or a file name.
When the runtime dynamic linker links an application before running, it reads the soname from
application’s executable file. This soname is libfoo.so.x. A symbolic link with this name must exist,
pointing to the actual library file. This allows loading the library, regardless of the Y component of a
version, because the soname does not change.
NOTE
The Y component of the version number is not limited to just a single number.
Additionally, some libraries encode their version in their name.
Reading soname from a file
To display the soname of a library file somelibrary:
$ objdump -p somelibrary | grep SONAME
Replace somelibrary with the actual file name of the library you wish to examine.
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2.3.3. Creating dynamic libraries with GCC
Dynamically linked libraries (shared objects) allow:
resource conservation through code reuse
increased security by making it easier to update the library code
Follow these steps to build and install a dynamic library from source.
Prerequisites
You must understand the soname mechanism.
GCC must be installed on the system.
You must have source code for a library.
Procedure
1. Change to the directory with library sources.
2. Compile each source file to an object file with the Position independent code option -fPIC:
$ gcc ... -c -fPIC some_file.c ...
The object files have the same file names as the original source code files, but their extension is
.o.
3. Link the shared library from the object files:
$ gcc -shared -o libfoo.so.x.y -Wl,-soname,libfoo.so.x some_file.o ...
The used major version number is X and minor version number Y.
4. Copy the libfoo.so.x.y file to an appropriate location, where the system’s dynamic linker can
find it. On Red Hat Enterprise Linux, the directory for libraries is /usr/lib64:
# cp libfoo.so.x.y /usr/lib64
Note that you need root permissions to manipulate files in this directory.
5. Create the symlink structure for soname mechanism:
# ln -s libfoo.so.x.y libfoo.so.x
# ln -s libfoo.so.x libfoo.so
Additional resources
The Linux Documentation Project — Program Library HOWTO — 3. Shared Libraries
2.3.4. Creating static libraries with GCC and ar
Creating libraries for static linking is possible through conversion of object files into a special type of
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Creating libraries for static linking is possible through conversion of object files into a special type of
archive file.
NOTE
Red Hat discourages the use of static linking for security reasons. Use static linking only
when necessary, especially against libraries provided by Red Hat. See Section 2.2.2,
“Static and dynamic linking” for more details.
Prerequisites
GCC and binutils must be installed on the system.
You must understand static and dynamic linking.
Source file(s) with functions to be shared as a library are available.
Procedure
1. Create intermediate object files with GCC.
$ gcc -c source_file.c ...
Append more source files if required. The resulting object files share the file name but use the
.o file name extension.
2. Turn the object files into a static library (archive) using the ar tool from the binutils package.
$ ar rcs libfoo.a source_file.o ...
File libfoo.a is created.
3. Use the nm command to inspect the resulting archive:
$ nm libfoo.a
4. Copy the static library file to the appropriate directory.
5. When linking against the library, GCC will automatically recognize from the .a file name
extension that the library is an archive for static linking.
$ gcc ... -lfoo ...
Additional resources
Linux manual page for ar(1):
$ man ar
2.4. MANAGING MORE CODE WITH MAKE
The GNU make utility, commonly abbreviated make, is a tool for controlling the generation of
executables from source files. make automatically determines which parts of a complex program have
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changed and need to be recompiled. make uses configuration files called Makefiles to control the way
programs are built.
2.4.1. GNU make and Makefile overview
To create a usable form (usually executable files) from the source files of a particular project, perform
several necessary steps. Record the actions and their sequence to be able to repeat them later.
Red Hat Enterprise Linux contains GNU make, a build system designed for this purpose.
Prerequisites
Understanding the concepts of compiling and linking
GNU make
GNU make reads Makefiles which contain the instructions describing the build process. A Makefile
contains multiple rules that describe a way to satisfy a certain condition ( target) with a specific action
(recipe). Rules can hierarchically depend on another rule.
Running make without any options makes it look for a Makefile in the current directory and attempt to
reach the default target. The actual Makefile file name can be one of Makefile, makefile, and
GNUmakefile. The default target is determined from the Makefile contents.
Makefile details
Makefiles use a relatively simple syntax for defining variables and rules, which consists of a target and a
recipe. The target specifies what is the output if a rule is executed. The lines with recipes must start with
the TAB character.
Typically, a Makefile contains rules for compiling source files, a rule for linking the resulting object files,
and a target that serves as the entry point at the top of the hierarchy.
Consider the following Makefile for building a C program which consists of a single file, hello.c.
This example shows that to reach the target all, file hello is required. To get hello, one needs hello.o
(linked by gcc), which in turn is created from hello.c (compiled by gcc).
The target all is the default target because it is the first target that does not start with a period (.).
Running make without any arguments is then identical to running make all, when the current directory
contains this Makefile.
Typical makefile
A more typical Makefile uses variables for generalization of the steps and adds a target "clean" - remove
everything but the source files.
all: hello
hello: hello.o
gcc hello.o -o hello
hello.o: hello.c
gcc -c hello.c -o hello.o
CC=gcc
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Adding more source files to such Makefile requires only adding them to the line where the SOURCE
variable is defined.
Additional resources
GNU make: Introduction — 2 An Introduction to Makefiles
Section 2.1, “Building Code with GCC”
2.4.2. Example: Building a C program using a Makefile
Build a sample C program using a Makefile by following the steps in this example.
Prerequisites
You must understand the concepts of Makefiles and make.
Procedure
1. Create a directory hellomake and change to this directory:
$ mkdir hellomake
$ cd hellomake
2. Create a file hello.c with the following contents:
3. Create a file Makefile with the following contents:
CFLAGS=-c -Wall
SOURCE=hello.c
OBJ=$(SOURCE:.c=.o)
EXE=hello
all: $(SOURCE) $(EXE)
$(EXE): $(OBJ)
$(CC) $(OBJ) -o $@
%.o: %.c
$(CC) $(CFLAGS) $< -o $@
clean:
rm -rf $(OBJ) $(EXE)
#include <stdio.h>
int main(int argc, char *argv[]) {
printf("Hello, World!\n");
return 0;
}
CC=gcc
CFLAGS=-c -Wall
SOURCE=hello.c
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IMPORTANT
The Makefile recipe lines must start with the tab character! When copying the
text above from the documentation, the cut-and-paste process may paste
spaces instead of tabs. If this happens, correct the issue manually.
4. Run make:
$ make
gcc -c -Wall hello.c -o hello.o
gcc hello.o -o hello
This creates an executable file hello.
5. Run the executable file hello:
$ ./hello
Hello, World!
6. Run the Makefile target clean to remove the created files:
$ make clean
rm -rf hello.o hello
Additional resources
Section 2.1.7, “Example: Building a C program with GCC (compiling and linking in one step)”
Section 2.1.9, “Example: Building a C++ program with GCC (compiling and linking in one step)”
2.4.3. Documentation resources for make
For more information about make, see the resources listed below.
Installed documentation
Use the man and info tools to view manual pages and information pages installed on your
system:
OBJ=$(SOURCE:.c=.o)
EXE=hello
all: $(SOURCE) $(EXE)
$(EXE): $(OBJ)
$(CC) $(OBJ) -o $@
%.o: %.c
$(CC) $(CFLAGS) $< -o $@
clean:
rm -rf $(OBJ) $(EXE)
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$ man make
$ info make
Online documentation
The GNU Make Manual hosted by the Free Software Foundation
2.5. CHANGES IN TOOLCHAIN SINCE RHEL 7
The following sections list changes in toolchain since the release of the described components in
Red Hat Enterprise Linux 7. See also Release notes for Red Hat Enterprise Linux 8.0 .
2.5.1. Changes in GCC in RHEL 8
In Red Hat Enterprise Linux 8, the GCC toolchain is based on the GCC 8.2 release series. Notable
changes since Red Hat Enterprise Linux 7 include:
Numerous general optimizations have been added, such as alias analysis, vectorizer
improvements, identical code folding, inter-procedural analysis, store merging optimization
pass, and others.
The Address Sanitizer has been improved.
The Leak Sanitizer for detection of memory leaks has been added.
The Undefined Behavior Sanitizer for detection of undefined behavior has been added.
Debug information can now be produced in the DWARF5 format. This capability is experimental.
The source code coverage analysis tool GCOV has been extended with various improvements.
Support for the OpenMP 4.5 specification has been added. Additionally, the offloading features
of the OpenMP 4.0 specification are now supported by the C, C++, and Fortran compilers.
New warnings and improved diagnostics have been added for static detection of certain likely
programming errors.
Source locations are now tracked as ranges rather than points, which allows much richer
diagnostics. The compiler now offers “fix-it” hints, suggesting possible code modifications. A
spell checker has been added to offer alternative names and ease detecting typos.
Security
GCC has been extended to provide tools to ensure additional hardening of the generated code.
For more details, see Section 2.5.2, “Security enhancements in GCC in RHEL 8” .
Architecture and processor support
Improvements to architecture and processor support include:
Multiple new architecture-specific options for the Intel AVX-512 architecture, a number of its
microarchitectures, and Intel Software Guard Extensions (SGX) have been added.
Code generation can now target the 64-bit ARM architecture LSE extensions, ARMv8.2-A 16-
CHAPTER 2. CREATING C OR C++ APPLICATIONS
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Code generation can now target the 64-bit ARM architecture LSE extensions, ARMv8.2-A 16-
bit Floating-Point Extensions (FPE), and ARMv8.2-A, ARMv8.3-A, and ARMv8.4-A architecture
versions.
Handling of the -march=native option on the ARM and 64-bit ARM architectures has been
fixed.
Support for the z13 and z14 processors of the 64-bit IBM Z architecture has been added.
Languages and standards
Notable changes related to languages and standards include:
The default standard used when compiling code in the C language has changed to C17 with
GNU extensions.
The default standard used when compiling code in the C++ language has changed to C++14 with
GNU extensions.
The C++ runtime library now supports the C++11 and C++14 standards.
The C++ compiler now implements the C++14 standard with many new features such as variable
templates, aggregates with non-static data member initializers, the extended constexpr
specifier, sized deallocation functions, generic lambdas, variable-length arrays, digit separators,
and others.
Support for the C language standard C11 has been improved: ISO C11 atomics, generic
selections, and thread-local storage are now available.
The new __auto_type GNU C extension provides a subset of the functionality of C++11 auto
keyword in the C language.
The _FloatN and _FloatNx type names specified by the ISO/IEC TS 18661-3:2015 standard are
now recognized by the C front end.
The default standard used when compiling code in the C language has changed to C17 with
GNU extensions. This has the same effect as using the --std=gnu17 option. Previously, the
default was C89 with GNU extensions.
GCC can now experimentally compile code using the C++17 language standard and certain
features from the C++20 standard.
Passing an empty class as an argument now takes up no space on the Intel 64 and AMD64
architectures, as required by the platform ABI. Passing or returning a class with only deleted
copy and move constructors now uses the same calling convention as a class with a non-trivial
copy or move constructor.
The value returned by the C++11 alignof operator has been corrected to match the C _Alignof
operator and return minimum alignment. To find the preferred alignment, use the GNU
extension __alignof__.
The main version of the libgfortran library for Fortran language code has been changed to 5.
Support for the Ada (GNAT), GCC Go, and Objective C/C++ languages has been removed. Use
the Go Toolset for Go code development.
Additional resources
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See also the Red Hat Enterprise Linux 8 Release Notes .
Using Go Toolset
2.5.2. Security enhancements in GCC in RHEL 8
This following are changes in GCC related to security and added since the release of Red Hat
Enterprise Linux 7.0.
New warnings
These warning options have been added:
Option Displays warnings for
-Wstringop-truncation Calls to bounded string manipulation functions such as strncat, strncpy,
and stpncpy that might either truncate the copied string or leave the
destination unchanged.
-Wclass-memaccess Objects of non-trivial class types manipulated in potentially unsafe ways by
raw memory functions such as memcpy or realloc.
The warning helps detect calls that bypass user-defined constructors or
copy-assignment operators, corrupt virtual table pointers, data members of
const-qualified types or references, or member pointers. The warning also
detects calls that would bypass access controls to data members.
-Wmisleading-
indentation
Places where the indentation of the code gives a misleading idea of the block
structure of the code to a human reader.
-Walloc-size-larger-
than=size
Calls to memory allocation functions where the amount of memory to
allocate exceeds size. Works also with functions where the allocation is
specified by multiplying two parameters and with any functions decorated
with attribute alloc_size.
-Walloc-zero Calls to memory allocation functions that attempt to allocate zero amount of
memory. Works also with functions where the allocation is specified by
multiplying two parameters and with any functions decorated with attribute
alloc_size.
-Walloca All calls to the alloca function.
-Walloca-larger-
than=size
Calls to the alloca function where the requested memory is more than size.
-Wvla-larger-than=size Definitions of Variable Length Arrays (VLA) that can either exceed the
specified size or whose bound is not known to be sufficiently constrained.
-Wformat-overflow=level Both certain and likely buffer overflow in calls to the sprintf family of
formatted output functions. For more details and explanation of the level
value, see the gcc(1) manual page.
CHAPTER 2. CREATING C OR C++ APPLICATIONS
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-Wformat-
truncation=level
Both certain and likely output truncation in calls to the snprintf family of
formatted output functions. For more details and explanation of the level
value, see the gcc(1) manual page.
-Wstringop-
overflow=type
Buffer overflow in calls to string handling functions such as memcpy and
strcpy. For more details and explanation of the level value, see the gcc(1)
manual page.
Option Displays warnings for
Warning improvements
These GCC warnings have been improved:
The -Warray-bounds option has been improved to detect more instances of out-of-bounds
array indices and pointer offsets. For example, negative or excessive indices into flexible array
members and string literals are detected.
The -Wrestrict option introduced in GCC 7 has been enhanced to detect many more instances
of overlapping accesses to objects via restrict-qualified arguments to standard memory and
string manipulation functions such as memcpy and strcpy.
The -Wnonnull option has been enhanced to detect a broader set of cases of passing null
pointers to functions that expect a non-null argument (decorated with attribute nonnull).
New UndefinedBehaviorSanitizer
A new run-time sanitizer for detecting undefined behavior called UndefinedBehaviorSanitizer has been
added. The following options are noteworthy:
Option Check
-fsanitize=float-divide-by-zero Detect floating-point division by zero.
-fsanitize=float-cast-overflow Check that the result of floating-point type to integer conversions
do not overflow.
-fsanitize=bounds Enable instrumentation of array bounds and detect out-of-bounds
accesses.
-fsanitize=alignment Enable alignment checking and detect various misaligned objects.
-fsanitize=object-size Enable object size checking and detect various out-of-bounds
accesses.
-fsanitize=vptr Enable checking of C++ member function calls, member accesses,
and some conversions between pointers to base and derived
classes. Additionally, detect when referenced objects do not have
correct dynamic type.
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-fsanitize=bounds-strict Enable strict checking of array bounds. This enables -
fsanitize=bounds and instrumentation of flexible array member-
like arrays.
-fsanitize=signed-integer-
overflow
Diagnose arithmetic overflows even on arithmetic operations with
generic vectors.
-fsanitize=builtin Diagnose at run time invalid arguments to __builtin_clz or
__builtin_ctz prefixed builtins. Includes checks from -
fsanitize=undefined.
-fsanitize=pointer-overflow Perform cheap run-time tests for pointer wrapping. Includes
checks from -fsanitize=undefined.
Option Check
New options for AddressSanitizer
These options have been added to AddressSanitizer:
Option Check
-fsanitize=pointer-compare Warn about comparison of pointers that point to a different
memory object.
-fsanitize=pointer-subtract Warn about subtraction of pointers that point to a different
memory object.
-fsanitize-address-use-after-
scope
Sanitize variables whose address is taken and used after a scope
where the variable is defined.
Other sanitizers and instrumentation
The option -fstack-clash-protection has been added to insert probes when stack space is
allocated statically or dynamically to reliably detect stack overflows and thus mitigate the attack
vector that relies on jumping over a stack guard page provided by the operating system.
A new option -fcf-protection=[full|branch|return|none] has been added to perform code
instrumentation and increase program security by checking that target addresses of control-
flow transfer instructions (such as indirect function call, function return, indirect jump) are valid.
Additional resources
For more details and explanation of the values supplied to some of the options above, see the
gcc(1) manual page:
$ man gcc
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2.5.3. Compatibility-breaking changes in GCC in RHEL 8
C++ ABI change in std::string and std::list
The Application Binary Interface (ABI) of the std::string and std::list classes from the libstdc++ library
changed between RHEL 7 (GCC 4.8) and RHEL 8 (GCC 8) to conform to the C++11 standard. The
libstdc++ library supports both the old and new ABI, but some other C++ system libraries do not. As a
consequence, applications that dynamically link against these libraries will need to be rebuilt. This affects
all C++ standard modes, including C++98. It also affects applications built with Red Hat Developer
Toolset compilers for RHEL 7, which kept the old ABI to maintain compatibility with the system libraries.
GCC no longer builds Ada, Go, and Objective C/C++ code
Capability for building code in the Ada (GNAT), GCC Go, and Objective C/C++ languages has been
removed from the GCC compiler.
To build Go code, use the Go Toolset instead.
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CHAPTER 3. DEBUGGING APPLICATIONS
Debugging applications is a very wide topic. This part provides a developer with the most common
techniques for debugging in multiple situations.
3.1. ENABLING DEBUGGING WITH DEBUGGING INFORMATION
To debug applications and libraries, debugging information is required. The following sections describe
how to obtain this information.
3.1.1. Debugging information
While debugging any executable code, two types of information allow the tools, and by extension the
programmer, to comprehend the binary code:
the source code text
a description of how the source code text relates to the binary code
Such information is called debugging information.
Red Hat Enterprise Linux uses the ELF format for executable binaries, shared libraries, or debuginfo
files. Within these ELF files, the DWARF format is used to hold the debug information.
To display DWARF information stored within an ELF file, run the readelf -w file command.
IMPORTANT
STABS is an older, less capable format, occasionally used with UNIX. Its use is
discouraged by Red Hat. GCC and GDB provide STABS production and consumption on
a best effort basis only. Some other tools such as Valgrind and elfutils do not work with
STABS.
Additional resources
The DWARF Debugging Standard
3.1.2. Enabling debugging of C and C++ applications with GCC
Because debugging information is large, it is not included in executable files by default. To enable
debugging of your C and C++ applications with it, you must explicitly instruct the compiler to create it.
To enable creation of debugging information with GCC when compiling and linking code, use the -g
option:
$ gcc ... -g ...
Optimizations performed by the compiler and linker can result in executable code which is hard
to relate to the original source code: variables may be optimized out, loops unrolled, operations
merged into the surrounding ones, and so on. This affects debugging negatively. For improved
debugging experience, consider setting the optimization with the -Og option. However,
changing the optimization level changes the executable code and may change the actual
behaviour including removing some bugs.
CHAPTER 3. DEBUGGING APPLICATIONS
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To also include macro definitions in the debug information, use the -g3 option instead of -g.
The -fcompare-debug GCC option tests code compiled by GCC with debug information and
without debug information. The test passes if the resulting two binary files are identical. This
test ensures that executable code is not affected by any debugging options, which further
ensures that there are no hidden bugs in the debug code. Note that using the -fcompare-debug
option significantly increases compilation time. See the GCC manual page for details about this
option.
Additional resources
Section 3.1, “Enabling Debugging with Debugging Information”
Using the GNU Compiler Collection (GCC) — Options for Debugging Your Program
Debugging with GDB — Debugging Information in Separate Files
The GCC manual page:
$ man gcc
3.1.3. Debuginfo and debugsource packages
The debuginfo and debugsource packages contain debugging information and debug source code for
programs and libraries. For applications and libraries installed in packages from the Red Hat
Enterprise Linux repositories, you can obtain separate debuginfo and debugsource packages from an
additional channel.
Debugging information package types
There are two types of packages available for debugging:
Debuginfo packages
The debuginfo packages provide debugging information needed to provide human-readable names
for binary code features. These packages contain .debug files, which contain DWARF debugging
information. These files are installed to the /usr/lib/debug directory.
Debugsource packages
The debugsource packages contain the source files used for compiling the binary code. With both
respective debuginfo and debugsource package installed, debuggers such as GDB or LLDB can
relate the execution of binary code to the source code. The source code files are installed to the
/usr/src/debug directory.
Differences from RHEL 7
In Red Hat Enterprise Linux 7, the debuginfo packages contained both kinds of information. Red Hat
Enterprise Linux 8 splits the source code data needed for debugging from the debuginfo packages into
separate debugsource packages.
Package names
A debuginfo or debugsource package provides debugging information valid only for a binary package
with the same name, version, release, and architecture:
Binary package: packagename-version-release.architecture.rpm
Debuginfo package: packagename-debuginfo-version-release.architecture.rpm
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Debugsource package: packagename-debugsource-version-release.architecture.rpm
Additional resources
Section 3.1.1, “Debugging information”
Section 1.2, “Enabling debug and source repositories”
3.1.4. Getting debuginfo packages for an application or library using GDB
Debugging information is required to debug code. For code that is installed from a package, the GNU
Debugger (GDB) automatically recognizes missing debug information, resolves the package name and
provides concrete advice on how to get the package.
Prerequisites
The application or library you want to debug must be installed on the system.
GDB and the debuginfo-install tool must be installed on the system.
Repositories providing debuginfo and debugsource packages must be configured and enabled
on the system. For details, see Enabling debug and source repositories.
Procedure
1. Start GDB attached to the application or library you want to debug. GDB automatically
recognizes missing debugging information and suggests a command to run.
$ gdb -q /bin/ls
Reading symbols from /bin/ls...Reading symbols from .gnu_debugdata for /usr/bin/ls...(no
debugging symbols found)...done.
(no debugging symbols found)...done.
Missing separate debuginfos, use: dnf debuginfo-install coreutils-8.30-6.el8.x86_64
(gdb)
2. Exit GDB: type q and confirm with Enter.
(gdb) q
3. Run the command suggested by GDB to install the required debuginfo packages:
# dnf debuginfo-install coreutils-8.30-6.el8.x86_64
The dnf package management tool provides a summary of the changes, asks for confirmation
and once you confirm, downloads and installs all the necessary files.
4. In case GDB is not able to suggest the debuginfo package, follow the procedure described in
Section 3.1.5, “Getting debuginfo packages for an application or library manually” .
Additional resources
How can I download or install debuginfo packages for RHEL systems? — Red Hat
Knowledgebase solution
CHAPTER 3. DEBUGGING APPLICATIONS
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3.1.5. Getting debuginfo packages for an application or library manually
You can determine manually which debuginfo packages you need to install by locating the executable
file and then finding the package that installs it.
NOTE
Red Hat recommends that you use GDB to determine the packages for installation . Use
this manual procedure only if GDB is not able to suggest the package to install.
Prerequisites
The application or library must be installed on the system.
The application or library was installed from a package.
The debuginfo-install tool must be available on the system.
Channels providing the debuginfo packages must be configured and enabled on the system.
Procedure
1. Find the executable file of the application or library.
a. Use the which command to find the application file.
$ which less
/usr/bin/less
b. Use the locate command to find the library file.
$ locate libz | grep so
/usr/lib64/libz.so.1
/usr/lib64/libz.so.1.2.11
If the original reasons for debugging include error messages, pick the result where the
library has the same additional numbers in its file name as those mentioned in the error
messages. If in doubt, try following the rest of the procedure with the result where the
library file name includes no additional numbers.
NOTE
The locate command is provided by the mlocate package. To install it and
enable its use:
# yum install mlocate
# updatedb
2. Search for a name and version of the package that provided the file:
$ rpm -qf /usr/lib64/libz.so.1.2.7
zlib-1.2.11-10.el8.x86_64
The output provides details for the installed package in the
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The output provides details for the installed package in the
name:epoch-version.release.architecture format.
IMPORTANT
If this step does not produce any results, it is not possible to determine which
package provided the binary file. There are several possible cases:
The file is installed from a package which is not known to package
management tools in their current configuration.
The file is installed from a locally downloaded and manually installed package.
Determining a suitable debuginfo package automatically is impossible in that
case.
Your package management tools are misconfigured.
The file is not installed from any package. In such a case, no respective
debuginfo package exists.
Because further steps depend on this one, you must resolve this situation or
abort this procedure. Describing the exact troubleshooting steps is beyond the
scope of this procedure.
3. Install the debuginfo packages using the debuginfo-install utility. In the command, use the
package name and other details you determined during the previous step:
# debuginfo-install zlib-1.2.11-10.el8.x86_64
Additional resources
How can I download or install debuginfo packages for RHEL systems? — Knowledgebase article
3.2. INSPECTING APPLICATION INTERNAL STATE WITH GDB
To find why an application does not work properly, control its execution and examine its internal state
with a debugger. This section describes how to use the GNU Debugger (GDB) for this task.
3.2.1. GNU debugger (GDB)
Red Hat Enterprise Linux contains the GNU debugger (GDB) which lets you investigate what is
happening inside a program through a command-line user interface.
GDB capabilities
A single GDB session can debug the following types of programs:
Multithreaded and forking programs
Multiple programs at once
Programs on remote machines or in containers with the gdbserver utility connected over a
TCP/IP network connection
Debugging requirements
CHAPTER 3. DEBUGGING APPLICATIONS
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To debug any executable code, GDB requires debugging information for that particular code:
For programs developed by you, you can create the debugging information while building the
code.
For system programs installed from packages, you must install their debuginfo packages.
3.2.2. Attaching GDB to a process
In order to examine a process, GDB must be attached to the process.
Prerequisites
GDB must be installed on the system
Starting a program with GDB
When the program is not running as a process, start it with GDB:
$ gdb program
Replace program with a file name or path to the program.
GDB sets up to start execution of the program. You can set up breakpoints and the gdb environment
before beginning the execution of the process with the run command.
Attaching GDB to an already running process
To attach GDB to a program already running as a process:
1. Find the process ID (pid) with the ps command:
$ ps -C program -o pid h
pid
Replace program with a file name or path to the program.
2. Attach GDB to this process:
$ gdb -p pid
Replace pid with an actual process ID number from the ps output.
Attaching an already running GDB to an already running process
To attach an already running GDB to an already running program:
1. Use the shell GDB command to run the ps command and find the program’s process ID ( pid):
(gdb) shell ps -C program -o pid h
pid
Replace program with a file name or path to the program.
2. Use the attach command to attach GDB to the program:
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(gdb) attach pid
Replace pid by an actual process ID number from the ps output.
NOTE
In some cases, GDB might not be able to find the respective executable file. Use the file
command to specify the path:
(gdb) file path/to/program
Additional resources
Debugging with GDB — 2.1 Invoking GDB
Debugging with GDB — 4.7 Debugging an Already-running Process
3.2.3. Stepping through program code with GDB
Once the GDB debugger is attached to a program, you can use a number of commands to control the
execution of the program.
Prerequisites
You must have the required debugging information available:
The program is compiled and built with debugging information, or
The relevant debuginfo packages are installed
GDB must be attached to the program to be debugged
GDB commands to step through the code
r (run)
Start the execution of the program. If run is executed with any arguments, those arguments are
passed on to the executable as if the program has been started normally. Users normally issue this
command after setting breakpoints.
start
Start the execution of the program but stop at the beginning of the program’s main function. If start
is executed with any arguments, those arguments are passed on to the executable as if the program
has been started normally.
c (continue)
Continue the execution of the program from the current state. The execution of the program will
continue until one of the following becomes true:
A breakpoint is reached.
A specified condition is satisfied.
A signal is received by the program.
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An error occurs.
The program terminates.
n (next)
Continue the execution of the program from the current state, until the next line of code in the
current source file is reached. The execution of the program will continue until one of the following
becomes true:
A breakpoint is reached.
A specified condition is satisfied.
A signal is received by the program.
An error occurs.
The program terminates.
s (step)
The step command also halts execution at each sequential line of code in the current source file.
However, if the execution is currently stopped at a source line containing a function call, GDB stops
the execution after entering the function call (rather than executing it).
until location
Continue the execution until the code location specified by the location option is reached.
fini (finish)
Resume the execution of the program and halt when execution returns from a function. The
execution of the program will continue until one of the following becomes true:
A breakpoint is reached.
A specified condition is satisfied.
A signal is received by the program.
An error occurs.
The program terminates.
q (quit)
Terminate the execution and exit GDB.
Additional resources
Section 3.2.5, “Using GDB breakpoints to stop execution at defined code locations”
Debugging with GDB — Starting your Program
Debugging with GDB — Continuing and Stepping
3.2.4. Showing program internal values with GDB
Displaying the values of a program’s internal variables is important for understanding of what the
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Displaying the values of a program’s internal variables is important for understanding of what the
program is doing. GDB offers multiple commands that you can use to inspect the internal variables. The
following are the most useful of these commands:
p (print)
Display the value of the argument given. Usually, the argument is the name of a variable of any
complexity, from a simple single value to a structure. An argument can also be an expression valid in
the current language, including the use of program variables and library functions, or functions
defined in the program being tested.
It is possible to extend GDB with pretty-printer Python or Guile scripts for customized display of data
structures (such as classes, structs) using the print command.
bt (backtrace)
Display the chain of function calls used to reach the current execution point, or the chain of functions
used up until execution was terminated. This is useful for investigating serious bugs (such as
segmentation faults) with elusive causes.
Adding the full option to the backtrace command displays local variables, too.
It is possible to extend GDB with frame filter Python scripts for customized display of data displayed
using the bt and info frame commands. The term frame refers to the data associated with a single
function call.
info
The info command is a generic command to provide information about various items. It takes an
option specifying the item to describe.
The info args command displays options of the function call that is the currently selected
frame.
The info locals command displays local variables in the currently selected frame.
For a list of the possible items, run the command help info in a GDB session:
(gdb) help info
l (list)
Show the line in the source code where the program stopped. This command is available only when
the program execution is stopped. While not strictly a command to show internal state, list helps the
user understand what changes to the internal state will happen in the next step of the program’s
execution.
Additional resources
The GDB Python API — Red Hat Developers Blog entry
Debugging with GDB — Pretty Printing
3.2.5. Using GDB breakpoints to stop execution at defined code locations
Often, only small portions of code are investigated. Breakpoints are markers that tell GDB to stop the
execution of a program at a certain place in the code. Breakpoints are most commonly associated with
source code lines. In that case, placing a breakpoint requires specifying the source file and line number.
To place a breakpoint:
CHAPTER 3. DEBUGGING APPLICATIONS
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Specify the name of the source code file and the line in that file:
(gdb) br file:line
When file is not present, name of the source file at the current point of execution is used:
(gdb) br line
Alternatively, use a function name to put the breakpoint on its start:
(gdb) br function_name
A program might encounter an error after a certain number of iterations of a task. To specify an
additional condition to halt execution:
(gdb) br file:line if condition
Replace condition with a condition in the C or C++ language. The meaning of file and line is the
same as above.
To inspect the status of all breakpoints and watchpoints:
(gdb) info br
To remove a breakpoint by using its number as displayed in the output of info br:
(gdb) delete number
To remove a breakpoint at a given location:
(gdb) clear file:line
Additional resources
Debugging with GDB — Breakpoints, Watchpoints, and Catchpoints
3.2.6. Using GDB watchpoints to stop execution on data access and changes
In many cases, it is advantageous to let the program execute until certain data changes or is accessed.
The following examples are the most common use cases.
Prerequisites
Understanding GDB
Using watchpoints in GDB
Watchpoints are markers which tell GDB to stop the execution of a program. Watchpoints are
associated with data: placing a watchpoint requires specifying an expression that describes a variable,
multiple variables, or a memory address.
To place a watchpoint for data change (write):
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(gdb) watch expression
Replace expression with an expression that describes what you want to watch. For variables,
expression is equal to the name of the variable.
To place a watchpoint for data access (read):
(gdb) rwatch expression
To place a watchpoint for any data access (both read and write):
(gdb) awatch expression
To inspect the status of all watchpoints and breakpoints:
(gdb) info br
To remove a watchpoint:
(gdb) delete num
Replace the num option with the number reported by the info br command.
Additional resources
Debugging with GDB — Setting Watchpoints
3.2.7. Debugging forking or threaded programs with GDB
Some programs use forking or threads to achieve parallel code execution. Debugging multiple
simultaneous execution paths requires special considerations.
Prerequisites
You must understand the concepts of process forking and threads.
Debugging forked programs with GDB
Forking is a situation when a program (parent) creates an independent copy of itself ( child). Use the
following settings and commands to affect what GDB does when a fork occurs:
The follow-fork-mode setting controls whether GDB follows the parent or the child after the
fork.
set follow-fork-mode parent
After a fork, debug the parent process. This is the default.
set follow-fork-mode child
After a fork, debug the child process.
show follow-fork-mode
Display the current setting of follow-fork-mode.
The set detach-on-fork setting controls whether the GDB keeps control of the other (not
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The set detach-on-fork setting controls whether the GDB keeps control of the other (not
followed) process or leaves it to run.
set detach-on-fork on
The process which is not followed (depending on the value of follow-fork-mode) is detached
and runs independently. This is the default.
set detach-on-fork off
GDB keeps control of both processes. The process which is followed (depending on the
value of follow-fork-mode) is debugged as usual, while the other is suspended.
show detach-on-fork
Display the current setting of detach-on-fork.
Debugging Threaded Programs with GDB
GDB has the ability to debug individual threads, and to manipulate and examine them independently. To
make GDB stop only the thread that is examined, use the commands set non-stop on and set target-
async on. You can add these commands to the .gdbinit file. After that functionality is turned on, GDB is
ready to conduct thread debugging.
GDB uses a concept of current thread. By default, commands apply to the current thread only.
info threads
Display a list of threads with their id and gid numbers, indicating the current thread.
thread id
Set the thread with the specified id as the current thread.
thread apply ids command
Apply the command command to all threads listed by ids. The ids option is a space-separated list of
thread ids. A special value all applies the command to all threads.
break location thread id if condition
Set a breakpoint at a certain location with a certain condition only for the thread number id.
watch expression thread id
Set a watchpoint defined by expression only for the thread number id.
command&
Execute command command and return immediately to the gdb prompt (gdb), continuing any code
execution in the background.
interrupt
Halt execution in the background.
Additional resources
Debugging with GDB — 4.10 Debugging Programs with Multiple Threads
Debugging with GDB — 4.11 Debugging Forks
3.3. RECORDING APPLICATION INTERACTIONS
The executable code of applications interacts with the code of the operating system and shared
libraries. Recording an activity log of these interactions can provide enough insight into the application’s
behavior without debugging the actual application code. Alternatively, analyzing an application’s
interactions can help pinpoint the conditions in which a bug manifests.
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3.3.1. Tools useful for recording application interactions
Red Hat Enterprise Linux offers multiple tools for analyzing an application’s interactions.
strace
The strace tool primarily enables logging of system calls (kernel functions) used by an application.
The strace tool can provide a detailed output about calls, because strace interprets
parameters and results with knowledge of the underlying kernel code. Numbers are turned
into the respective constant names, bitwise combined flags expanded to flag list, pointers to
character arrays dereferenced to provide the actual string, and more. Support for more
recent kernel features may be lacking.
You can filter the traced calls to reduce the amount of captured data.
The use of strace does not require any particular setup except for setting up the log filter.
Tracing the application code with strace results in significant slowdown of the application’s
execution. As a result, strace is not suitable for many production deployments. As an
alternative, consider using ltrace or SystemTap.
The version of strace available in Red Hat Developer Toolset can also perform system call
tampering. This capability is useful for debugging.
ltrace
The ltrace tool enables logging of an application’s user space calls into shared objects (dynamic
libraries).
The ltrace tool enables tracing calls to any library.
You can filter the traced calls to reduce the amount of captured data.
The use of ltrace does not require any particular setup except for setting up the log filter.
The ltrace tool is lightweight and fast, offering an alternative to strace: it is possible to trace
the respective interfaces in libraries such as glibc with ltrace instead of tracing kernel
functions with strace.
Because ltrace does not handle a known set of calls like strace, it does not attempt to
explain the values passed to library functions. The ltrace output contains only raw numbers
and pointers. The interpretation of ltrace output requires consulting the actual interface
declarations of the libraries present in the output.
NOTE
In Red Hat Enterprise Linux 8, a known issue prevents ltrace from tracing system
executable files. This limitation does not apply to executable files built by users.
SystemTap
SystemTap is an instrumentation platform for probing running processes and kernel activity on the
Linux system. SystemTap uses its own scripting language for programming custom event handlers.
Compared to using strace and ltrace, scripting the logging means more work in the initial
setup phase. However, the scripting capabilities extend SystemTap’s usefulness beyond just
producing logs.
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SystemTap works by creating and inserting a kernel module. The use of SystemTap is
efficient and does not create a significant slowdown of the system or application execution
on its own.
SystemTap comes with a set of usage examples.
GDB
The GNU Debugger (GDB) is primarily meant for debugging, not logging. However, some of its
features make it useful even in the scenario where an application’s interaction is the primary activity
of interest.
With GDB, it is possible to conveniently combine the capture of an interaction event with
immediate debugging of the subsequent execution path.
GDB is best suited for analyzing response to infrequent or singular events, after the initial
identification of problematic situation by other tools. Using GDB in any scenario with
frequent events becomes inefficient or even impossible.
Additional resources
Getting started with SystemTap
Red Hat Developer Toolset User Guide
3.3.2. Monitoring an application’s system calls with strace
The strace tool enables monitoring the system (kernel) calls performed by an application.
Prerequisites
You must have strace installed on the system.
Procedure
1. Identify the system calls to monitor.
2. Start strace and attach it to the program.
If the program you want to monitor is not running, start strace and specify the program:
$ strace -fvttTyy -s 256 -e trace=call program
If the program is already running, find its process id (pid) and attach strace to it:
$ ps -C program
(...)
$ strace -fvttTyy -s 256 -e trace=call -ppid
Replace call with the system calls to be displayed. You can use the -e trace=call option
multiple times. If left out, strace will display all system call types. See the strace(1) manual
page for more information.
If you do not want to trace any forked processes or threads, leave out the -f option.
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3. The strace tool displays the system calls made by the application and their details.
In most cases, an application and its libraries make a large number of calls and strace output
appears immediately, if no filter for system calls is set.
4. The strace tool exits when the program exits.
To terminate the monitoring before the traced program exits, press Ctrl+C.
If strace started the program, the program terminates together with strace.
If you attached strace to an already running program, the program terminates together
with strace.
5. Analyze the list of system calls done by the application.
Problems with resource access or availability are present in the log as calls returning errors.
Values passed to the system calls and patterns of call sequences provide insight into the
causes of the application’s behaviour.
If the application crashes, the important information is probably at the end of log.
The output contains a lot of unnecessary information. However, you can construct a more
precise filter for the system calls of interest and repeat the procedure.
NOTE
It is advantageous to both see the output and save it to a file. Use the tee command to
achieve this:
$ strace ... |& tee your_log_file.log
Additional resources
The strace(1) manual page:
$ man strace
How do I use strace to trace system calls made by a command? — Knowledgebase article
Red Hat Developer Toolset User Guide — Chapter strace
3.3.3. Monitoring application’s library function calls with ltrace
The ltrace tool enables monitoring an application’s calls to functions available in libraries (shared
objects).
NOTE
In Red Hat Enterprise Linux 8, a known issue prevents ltrace from tracing system
executable files. This limitation does not apply to executable files built by users.
Prerequisites
You must have ltrace installed on the system.
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Procedure
1. Identify the libraries and functions of interest, if possible.
2. Start ltrace and attach it to the program.
If the program you want to monitor is not running, start ltrace and specify program:
$ ltrace -f -l library -e function program
If the program is already running, find its process id (pid) and attach ltrace to it:
$ ps -C program
(...)
$ ltrace -f -l library -e function program -ppid
Use the -e, -f and -l options to filter the output:
Supply the function names to be displayed as function. The -e function option can be
used multiple times. If left out, ltrace displays calls to all functions.
Instead of specifying functions, you can specify whole libraries with the -l library option.
This option behaves similarly to the -e function option.
If you do not want to trace any forked processes or threads, leave out the -f option.
See the ltrace(1)_ manual page for more information.
3. ltrace displays the library calls made by the application.
In most cases, an application makes a large number of calls and ltrace output displays
immediately, if no filter is set.
4. ltrace exits when the program exits.
To terminate the monitoring before the traced program exits, press ctrl+C.
If ltrace started the program, the program terminates together with ltrace.
If you attached ltrace to an already running program, the program terminates together with
ltrace.
5. Analyze the list of library calls done by the application.
If the application crashes, the important information is probably at the end of log.
The output contains a lot of unnecessary information. However, you can construct a more
precise filter and repeat the procedure.
NOTE
It is advantageous to both see the output and save it to a file. Use the tee command to
achieve this:
$ ltrace ... |& tee your_log_file.log
Additional resources
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The ltrace(1) manual page:
$ man ltrace
Red Hat Developer Toolset User Guide — Chapter ltrace
3.3.4. Monitoring application’s system calls with SystemTap
The SystemTap tool enables registering custom event handlers for kernel events. In comparison with the
strace tool, it is harder to use but more efficient and enables more complicated processing logic. A
SystemTap script called strace.stp is installed together with SystemTap and provides an approximation
of strace functionality using SystemTap.
Prerequisites
SystemTap and the respective kernel packages must be installed on the system.
Procedure
1. Find the process ID (pid) of the process you want to monitor:
$ ps -aux
2. Run SystemTap with the strace.stp script:
# stap /usr/share/systemtap/examples/process/strace.stp -x pid
The value of pid is the process id.
The script is compiled to a kernel module, which is then loaded. This introduces a slight delay
between entering the command and getting the output.
3. When the process performs a system call, the call name and its parameters are printed to the
terminal.
4. The script exits when the process terminates, or when you press Ctrl+C.
3.3.5. Using GDB to intercept application system calls
GNU Debugger (GDB) lets you stop an execution in various situations that arise during program
execution. To stop the execution when the program performs a system call, use a GDB catchpoint.
Prerequisites
You must understand the usage of GDB breakpoints.
GDB must be attached to the program.
Procedure
1. Set the catchpoint:
(gdb) catch syscall syscall-name
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The command catch syscall sets a special type of breakpoint that halts execution when the
program performs a system call.
The syscall-name option specifies the name of the call. You can specify multiple catchpoints
for various system calls. Leaving out the syscall-name option causes GDB to stop on any
system call.
2. Start execution of the program.
If the program has not started execution, start it:
(gdb) r
If the program execution is halted, resume it:
(gdb) c
3. GDB halts execution after the program performs any specified system call.
Additional resources
Section 3.2.4, “Showing program internal values with GDB”
Section 3.2.3, “Stepping through program code with GDB”
Debugging with GDB — Setting Watchpoints
3.3.6. Using GDB to intercept handling of signals by applications
GNU Debugger (GDB) lets you stop the execution in various situations that arise during program
execution. To stop the execution when the program receives a signal from the operating system, use a
GDB catchpoint.
Prerequisites
You must understand the usage of GDB breakpoints.
GDB must be attached to the program.
Procedure
1. Set the catchpoint:
(gdb) catch signal signal-type
The command catch signal sets a special type of a breakpoint that halts execution when a
signal is received by the program. The signal-type option specifies the type of the signal. Use
the special value 'all' to catch all signals.
2. Let the program run.
If the program has not started execution, start it:
(gdb) r
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If the program execution is halted, resume it:
(gdb) c
3. GDB halts execution after the program receives any specified signal.
Additional resources
Section 3.2.4, “Showing program internal values with GDB”
Stepping through program code with GDB
Debugging With GDB — 5.1.3 Setting Catchpoints
3.4. DEBUGGING A CRASHED APPLICATION
Sometimes, it is not possible to debug an application directly. In these situations, you can collect
information about the application at the moment of its termination and analyze it afterwards.
3.4.1. Core dumps: what they are and how to use them
A core dump is a copy of a part of the application’s memory at the moment the application stopped
working, stored in the ELF format. It contains all the application’s internal variables and stack, which
enables inspection of the application’s final state. When augmented with the respective executable file
and debugging information, it is possible to analyze a core dump file with a debugger in a way similar to
analyzing a running program.
The Linux operating system kernel can record core dumps automatically, if this functionality is enabled.
Alternatively, you can send a signal to any running application to generate a core dump regardless of its
actual state.
WARNING
Some limits might affect the ability to generate a core dump. To see the current
limits:
$ ulimit -a
3.4.2. Recording application crashes with core dumps
To record application crashes, set up core dump saving and add information about the system.
Procedure
1. To enable core dumps, ensure that the /etc/systemd/system.conf file contains the following
lines:
DumpCore=yes
DefaultLimitCORE=infinity
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You can also add comments describing if these settings were previously present, and what the
previous values were. This will enable you to reverse these changes later, if needed. Comments
are lines starting with the # character.
Changing the file requires administrator level access.
2. Apply the new configuration:
# systemctl daemon-reexec
3. Remove the limits for core dump sizes:
# ulimit -c unlimited
To reverse this change, run the command with value 0 instead of unlimited.
4. Install the sos package which provides the sosreport utility for collecting system information:
# yum install sos
5. When an application crashes, a core dump is generated and handled by systemd-coredump.
6. Create an SOS report to provide additional information about the system:
# sosreport
This creates a .tar archive containing information about your system, such as copies of
configuration files.
7. Locate and export the core dump:
$ coredumpctl list executable-name
$ coredumpctl dump executable-name > /path/to/file-for-export
If the application crashed multiple times, output of the first command lists more captured core
dumps. In that case, construct for the second command a more precise query using the other
information. See the coredumpctl(1) manual page for details.
8. Transfer the core dump and the SOS report to the computer where the debugging will take
place. Transfer the executable file, too, if it is known.
IMPORTANT
When the executable file is not known, subsequent analysis of the core file
identifies it.
9. Optional: Remove the core dump and SOS report after transferring them, to free up disk space.
Additional resources
Managing systemd in the document Configuring basic system settings
How to enable core file dumps when an application crashes or segmentation faults — a
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How to enable core file dumps when an application crashes or segmentation faults — a
Knowledge Base article
What is a sosreport and how to create one in Red Hat Enterprise Linux 4.6 and later? — a
Knowledge Base article
3.4.3. Inspecting application crash states with core dumps
Prerequisites
You must have a core dump file and sosreport from the system where the crash occurred.
GDB and elfutils must be installed on your system.
Procedure
1. To identify the executable file where the crash occurred, run the eu-unstrip command with the
core dump file:
$ eu-unstrip -n --core=./core.9814
0x400000+0x207000 2818b2009547f780a5639c904cded443e564973e@0x400284
/usr/bin/sleep /usr/lib/debug/bin/sleep.debug [exe]
0x7fff26fff000+0x1000 1e2a683b7d877576970e4275d41a6aaec280795e@0x7fff26fff340 . -
linux-vdso.so.1
0x35e7e00000+0x3b6000
374add1ead31ccb449779bc7ee7877de3377e5ad@0x35e7e00280 /usr/lib64/libc-2.14.90.so
/usr/lib/debug/lib64/libc-2.14.90.so.debug libc.so.6
0x35e7a00000+0x224000
3ed9e61c2b7e707ce244816335776afa2ad0307d@0x35e7a001d8 /usr/lib64/ld-2.14.90.so
/usr/lib/debug/lib64/ld-2.14.90.so.debug ld-linux-x86-64.so.2
The output contains details for each module on a line, separated by spaces. The information is
listed in this order:
1. The memory address where the module was mapped
2. The build-id of the module and where in the memory it was found
3. The module’s executable file name, displayed as - when unknown, or as . when the module
has not been loaded from a file
4. The source of debugging information, displayed as a file name when available, as . when
contained in the executable file itself, or as - when not present at all
5. The shared library name (soname) or [exe] for the main module
In this example, the important details are the file name /usr/bin/sleep and the build-id
2818b2009547f780a5639c904cded443e564973e on the line containing the text [exe]. With this
information, you can identify the executable file required for analyzing the core dump.
2. Get the executable file that crashed.
If possible, copy it from the system where the crash occurred. Use the file name extracted
from the core file.
You can also use an identical executable file on your system. Each executable file built on
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You can also use an identical executable file on your system. Each executable file built on
Red Hat Enterprise Linux contains a note with a unique build-id value. Determine the build-
id of the relevant locally available executable files:
$ eu-readelf -n executable_file
Use this information to match the executable file on the remote system with your local
copy. The build-id of the local file and build-id listed in the core dump must match.
Finally, if the application is installed from an RPM package, you can get the executable file
from the package. Use the sosreport output to find the exact version of the package
required.
3. Get the shared libraries used by the executable file. Use the same steps as for the executable
file.
4. If the application is distributed as a package, load the executable file in GDB, to display hints for
missing debuginfo packages. For more details, see Section 3.1.4, “Getting debuginfo packages
for an application or library using GDB”.
5. To examine the core file in detail, load the executable file and core dump file with GDB:
$ gdb -e executable_file -c core_file
Further messages about missing files and debugging information help you identify what is
missing for the debugging session. Return to the previous step if needed.
If the application’s debugging information is available as a file instead of as a package, load this
file in GDB with the symbol-file command:
(gdb) symbol-file program.debug
Replace program.debug with the actual file name.
NOTE
It might not be necessary to install the debugging information for all executable
files contained in the core dump. Most of these executable files are libraries used
by the application code. These libraries might not directly contribute to the
problem you are analyzing, and you do not need to include debugging information
for them.
6. Use the GDB commands to inspect the state of the application at the moment it crashed. See
Inspecting Application Internal State with GDB.
NOTE
When analyzing a core file, GDB is not attached to a running process. Commands
for controlling execution have no effect.
Additional resources
Debugging with GDB — 2.1.1 Choosing Files
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Debugging with GDB — 18.1 Commands to Specify Files
Debugging with GDB — 18.3 Debugging Information in Separate Files
3.4.4. Creating and accessing a core dump with coredumpctl
The coredumpctl tool of systemd can significantly streamline working with core dumps on the machine
where the crash happened. This procedure outlines how to capture a core dump of unresponsive
process.
Prerequisites
The system must be configured to use systemd-coredump for core dump handling. To verify
this is true:
$ sysctl kernel.core_pattern
The configuration is correct if the output starts with the following:
kernel.core_pattern = |/usr/lib/systemd/systemd-coredump
Procedure
1. Find the PID of the hung process, based on a known part of the executable file name:
$ pgrep -a executable-name-fragment
This command will output a line in the form
PID command-line
Use the command-line value to verify that the PID belongs to the intended process.
For example:
$ pgrep -a bc
5459 bc
2. Send an abort signal to the process:
# kill -ABRT PID
3. Verify that the core has been captured by coredumpctl:
$ coredumpctl list PID
For example:
$ coredumpctl list 5459
TIME PID UID GID SIG COREFILE EXE
Thu 2019-11-07 15:14:46 CET 5459 1000 1000 6 present /usr/bin/bc
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4. Further examine or use the core file as needed.
You can specify the core dump by PID and other values. See the coredumpctl(1) manual page
for further details.
To show details of the core file:
$ coredumpctl info PID
To load the core file in the GDB debugger:
$ coredumpctl debug PID
Depending on availability of debugging information, GDB will suggest commands to run,
such as:
Missing separate debuginfos, use: dnf debuginfo-install bc-1.07.1-5.el8.x86_64
For more details on this process, see Section 3.1.4, “Getting debuginfo packages for an
application or library using GDB”.
To export the core file for further processing elsewhere:
$ coredumpctl dump PID > /path/to/file_for_export
Replace /path/to/file_for_export with the file where you want to put the core dump.
3.4.5. Dumping process memory with gcore
The workflow of core dump debugging enables the analysis of the program’s state offline. In some cases,
you can use this workflow with a program that is still running, such as when it is hard to access the
environment with the process. You can use the gcore command to dump memory of any process while it
is still running.
Prerequisites
You must understand what core dumps are and how they are created.
GDB must be installed on the system.
Procedure
1. Find out the process id (pid). Use tools such as ps, pgrep, and top:
$ ps -C some-program
2. Dump the memory of this process:
$ gcore -o filename pid
This creates a file filename and dumps the process memory in it. While the memory is being
dumped, the execution of the process is halted.
3. After the core dump is finished, the process resumes normal execution.
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4. Create an SOS report to provide additional information about the system:
# sosreport
This creates a tar archive containing information about your system, such as copies of
configuration files.
5. Transfer the program’s executable file, core dump, and the SOS report to the computer where
the debugging will take place.
6. Optional: Remove the core dump and SOS report after transferring them, to free up disk space.
Additional resources
How to obtain a core file without restarting an application? — Knowledgebase article
3.4.6. Dumping protected process memory with GDB
You can mark the memory of processes as not to be dumped. This can save resources and ensure
additional security when the process memory contains sensitive data: for example, in banking or
accounting applications or on whole virtual machines. Both kernel core dumps (kdump) and manual
core dumps (gcore, GDB) do not dump memory marked this way.
In some cases, you must dump the whole contents of the process memory regardless of these
protections. This procedure shows how to do this using the GDB debugger.
Prerequisites
You must understand what core dumps are.
GDB must be installed on the system.
GDB must be already attached to the process with protected memory.
Procedure
1. Set GDB to ignore the settings in the /proc/PID/coredump_filter file:
(gdb) set use-coredump-filter off
2. Set GDB to ignore the memory page flag VM_DONTDUMP:
(gdb) set dump-excluded-mappings on
3. Dump the memory:
(gdb) gcore core-file
Replace core-file with name of file where you want to dump the memory.
Additional resources
Debugging with GDB - How to Produce a Core File from Your Program
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3.5. COMPATIBILITY-BREAKING CHANGES IN GDB
The version of GDB provided in Red Hat Enterprise Linux 8 contains a number of changes that break
compatibility, especially for cases where the GDB output is read directly from the terminal. The
following sections provide more details about these changes.
Parsing output of GDB is not recommended. Prefer scripts using the Python GDB API or the GDB
Machine Interface (MI).
GDBserver now starts inferiors with shell
To enable expansion and variable substitution in inferior command line arguments, GDBserver now
starts the inferior in a shell, same as GDB.
To disable using the shell:
When using the target extended-remote GDB command, disable shell with the set startup-
with-shell off command.
When using the target remote GDB command, disable shell with the --no-startup-with-shell
option of GDBserver.
Example 3.1. Example of shell expansion in remote GDB inferiors
This example shows how running the /bin/echo /* command through GDBserver differs on Red Hat
Enterprise Linux versions 7 and 8:
On RHEL 7:
$ gdbserver --multi :1234
$ gdb -batch -ex 'target extended-remote :1234' -ex 'set remote exec-file /bin/echo' -ex
'file /bin/echo' -ex 'run /*'
/*
On RHEL 8:
$ gdbserver --multi :1234
$ gdb -batch -ex 'target extended-remote :1234' -ex 'set remote exec-file /bin/echo' -ex
'file /bin/echo' -ex 'run /*'
/bin /boot (...) /tmp /usr /var
gcj support removed
Support for debugging Java programs compiled with the GNU Compiler for Java (gcj) has been
removed.
New syntax for symbol dumping maintenance commands
The symbol dumping maintenance commands syntax now includes options before file names. As a
result, commands that worked with GDB in RHEL 7 do not work in RHEL 8.
As an example, the following command no longer stores symbols in a file, but produces an error message:
(gdb) maintenance print symbols /tmp/out main.c
The new syntax for the symbol dumping maintenance commands is:
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maint print symbols [-pc address] [--] [filename]
maint print symbols [-objfile objfile] [-source source] [--] [filename]
maint print psymbols [-objfile objfile] [-pc address] [--] [filename]
maint print psymbols [-objfile objfile] [-source source] [--] [filename]
maint print msymbols [-objfile objfile] [--] [filename]
Thread numbers are no longer global
Previously, GDB used only global thread numbering. The numbering has been extended to be displayed
per inferior in the form inferior_num.thread_num, such as 2.1. As a consequence, thread numbers in the
$_thread convenience variable and in the InferiorThread.num Python attribute are no longer unique
between inferiors.
GDB now stores a second thread ID per thread, called the global thread ID, which is the new equivalent
of thread numbers in previous releases. To access the global thread number, use the $_gthread
convenience variable and InferiorThread.global_num Python attribute.
For backwards compatibility, the Machine Interface (MI) thread IDs always contains the global IDs.
Example 3.2. Example of GDB thread number changes
On Red Hat Enterprise Linux 7:
# debuginfo-install coreutils
$ gdb -batch -ex 'file echo' -ex start -ex 'add-inferior' -ex 'inferior 2' -ex 'file echo' -ex start -ex 'info
threads' -ex 'pring $_thread' -ex 'inferior 1' -ex 'pring $_thread'
(...)
Id Target Id Frame
* 2 process 203923 "echo" main (argc=1, argv=0x7fffffffdb88) at src/echo.c:109
1 process 203914 "echo" main (argc=1, argv=0x7fffffffdb88) at src/echo.c:109
$1 = 2
(...)
$2 = 1
On Red Hat Enterprise Linux 8:
# dnf debuginfo-install coreutils
$ gdb -batch -ex 'file echo' -ex start -ex 'add-inferior' -ex 'inferior 2' -ex 'file echo' -ex start -ex 'info
threads' -ex 'pring $_thread' -ex 'inferior 1' -ex 'pring $_thread'
(...)
Id Target Id Frame
1.1 process 4106488 "echo" main (argc=1, argv=0x7fffffffce58) at ../src/echo.c:109
* 2.1 process 4106494 "echo" main (argc=1, argv=0x7fffffffce58) at ../src/echo.c:109
$1 = 1
(...)
$2 = 1
Memory for value contents can be limited
Previously, GDB did not limit the amount of memory allocated for value contents. As a consequence,
debugging incorrect programs could cause GDB to allocate too much memory. The max-value-size
setting has been added to enable limiting the amount of allocated memory. The default value of this
limit is 64 KiB. As a result, GDB in Red Hat Enterprise Linux 8 will not display too large values, but report
that the value is too large instead.
As an example, printing a value defined as char s[128*1024]; produces different results:
CHAPTER 3. DEBUGGING APPLICATIONS
63
On Red Hat Enterprise Linux 7, $1 = 'A' <repeats 131072 times>
On Red Hat Enterprise Linux 8, value requires 131072 bytes, which is more than max-value-
size
Sun version of stabs format no longer supported
Support for the Sun version of the stabs debug file format has been removed. The stabs format
produced by GCC in RHEL with the gcc -gstabs option is still supported by GDB.
Sysroot handling changes
The set sysroot path command specifies system root when searching for files needed for debugging.
Directory names supplied to this command may now be prefixed with the string target: to make GDB
read the shared libraries from the target system (both local and remote). The formerly available remote:
prefix is now treated as target:. Additionally, the default system root value has changed from an empty
string to target: for backward compatibility.
The specified system root is prepended to the file name of the main executable, when GDB starts
processes remotely, or when it attaches to already running processes (both local and remote). This
means that for remote processes, the default value target: makes GDB always try to load the
debugging information from the remote system. To prevent this, run the set sysroot command before
the target remote command so that local symbol files are found before the remote ones.
HISTSIZE no longer controls GDB command history size
Previously, GDB used the HISTSIZE environment variable to determine how long command history
should be kept. GDB has been changed to use the GDBHISTSIZE environment variable instead. This
variable is specific only to GDB. The possible values and their effects are:
a positive number - use command history of this size,
-1 or an empty string - keep history of all commands,
non-numeric values - ignored.
Completion limiting added
The maximum number of candidates considered during completion can now be limited using the set
max-completions command. To show the current limit, run the show max-completions command.
The default value is 200. This limit prevents GDB from generating excessively large completion lists and
becoming unresponsive.
As an example, the output after the input p <tab><tab> is:
on RHEL 7: Display all 29863 possibilities? (y or n)
on RHEL 8: Display all 200 possibilities? (y or n)
HP-UX XDB compatibility mode removed
The -xdb option for the HP-UX XDB compatibility mode has been removed from GDB.
Handling signals for threads
Previously, GDB could deliver a signal to the current thread instead of the thread for which the signal
was actually sent. This bug has been fixed, and GDB now always passes the signal to the correct thread
when resuming execution.
Additionally, the signal command now always correctly delivers the requested signal to the current
thread. If the program is stopped for a signal and the user switched threads, GDB asks for confirmation.
Breakpoint modes always-inserted off and auto merged
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The breakpoint always-inserted setting has been changed. The auto value and corresponding
behavior has been removed. The default value is now off. Additionally, the off value now causes GDB to
not remove breakpoints from the target until all threads stop.
remotebaud commands no longer supported
The set remotebaud and show remotebaud commands are no longer supported. Use the set serial
baud and show serial baud commands instead.
3.6. DEBUGGING APPLICATIONS IN CONTAINERS
You can use various command-line tools tailored to different aspects of troubleshooting. The following
provides categories along with common command-line tools.
NOTE
This is not a complete list of command-line tools. The choice of tool for debugging a
container application is heavily based on the container image and your use case.
For instance, the systemctl, journalctl, ip, netstat, ping, traceroute, perf, iostat tools
may need root access because they interact with system-level resources such as
networking, systemd services, or hardware performance counters, which are restricted in
rootless containers for security reasons.
Rootless containers operate without requiring elevated privileges, running as non-root users within user
namespaces to provide improved security and isolation from the host system. They offer limited
interaction with the host, reduced attack surface, and enhanced security by mitigating the risk of
privilege escalation vulnerabilities.
Rootful containers run with elevated privileges, typically as the root user, granting full access to system
resources and capabilities. While rootful containers offer greater flexibility and control, they pose
security risks due to their potential for privilege escalation and exposure of the host system to
vulnerabilities.
For more information about rootful and rootless containers, see Setting up rootless containers,
Upgrading to rootless containers , and Special considerations for rootless containers .
Systemd and Process Management Tools
systemctl
Controls systemd services within containers, allowing start, stop, enable, and disable operations.
journalctl
Views logs generated by systemd services, aiding in troubleshooting container issues.
Networking Tools
ip
Manages network interfaces, routing, and addresses within containers.
netstat
Displays network connections, routing tables, and interface statistics.
ping
Verifies network connectivity between containers or hosts.
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traceroute
Identifies the path packets take to reach a destination, useful for diagnosing network issues.
Process and Performance Tools
ps
Lists currently running processes within containers.
top
Provides real-time insights into resource usage by processes within containers.
htop
Interactive process viewer for monitoring resource utilization.
perf
CPU performance profiling, tracing, and monitoring, aiding in pinpointing performance bottlenecks
within the system or applications.
vmstat
Reports virtual memory statistics within containers, aiding in performance analysis.
iostat
Monitors input/output statistics for block devices within containers.
gdb (GNU Debugger)
A command-line debugger that helps in examining and debugging programs by allowing users to
track and control their execution, inspect variables, and analyze memory and registers during runtime.
For more information, see the Debugging applications within Red Hat OpenShift containers article.
strace
Intercepts and records system calls made by a program, aiding in troubleshooting by revealing
interactions between the program and the operating system.
Security and Access Control Tools
sudo
Enables executing commands with elevated privileges.
chroot
Changes the root directory for a command, helpful in testing or troubleshooting within a different
root directory.
Podman-Specific Tools
podman logs
Batch-retrieves whatever logs are present for one or more containers at the time of execution.
podman inspect
Displays the low-level information on containers and images as identified by name or ID.
podman events
Monitor and print events that occur in Podman. Each event includes a timestamp, a type, a status, a
name (if applicable), and an image (if applicable). The default logging mechanism is journald.
podman run --health-cmd
Use the health check to determine the health or readiness of the process running inside the
container.
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podman top
Display the running processes of the container.
podman exec
Running commands in or attaching to a running container is extremely useful to get a better
understanding of what is happening in the container.
podman export
When the container fails, it is basically impossible to know what happened. Exporting the filesystem
structure from the container will allow for checking other logs files that may not be in the mounted
volumes.
Additional resources
Debugging applications within Red Hat OpenShift containers
gdb
Debugging a Crashed Application
Core dump, sosreport, gdb, ps, core.
Troubleshooting Kubernetes
Docker exec + env, netstat, kubectl, etcdctl, journalctl, docker logs
Tips and Tricks for containerizing services
Watch, podman logs, systemctl, podman exec/kill/restart, podman insect, podman top,
podman exec, podman export, paunch
External links
Ten tips for debugging Docker containers
CHAPTER 3. DEBUGGING APPLICATIONS
67
CHAPTER 4. ADDITIONAL TOOLSETS FOR DEVELOPMENT
4.1. USING GCC TOOLSET
4.1.1. What is GCC Toolset
Red Hat Enterprise Linux 8 introduces GCC Toolset, an Application Stream containing more up-to-date
versions of development and performance analysis tools. GCC Toolset is similar to Red Hat Developer
Toolset for RHEL 7.
GCC Toolset is available as an Application Stream in the form of a software collection in the AppStream
repository. GCC Toolset is fully supported under Red Hat Enterprise Linux Subscription Level
Agreements, is functionally complete, and is intended for production use. Applications and libraries
provided by GCC Toolset do not replace the Red Hat Enterprise Linux system versions, do not override
them, and do not automatically become default or preferred choices. Using a framework called software
collections, an additional set of developer tools is installed into the /opt/ directory and is explicitly
enabled by the user on demand using the scl utility. Unless noted otherwise for specific tools or
features, GCC Toolset is available for all architectures supported by Red Hat Enterprise Linux.
4.1.2. Installing GCC Toolset
Installing GCC Toolset on a system installs the main tools and all necessary dependencies. Note that
some parts of the toolset are not installed by default and must be installed separately.
Procedure
To install GCC Toolset version N:
# yum install gcc-toolset-N
4.1.3. Installing individual packages from GCC Toolset
To install only certain tools from GCC Toolset instead of the whole toolset, list the available packages
and install the selected ones with the yum package management tool. This procedure is useful also for
packages that are not installed by default with the toolset.
Procedure
1. List the packages available in GCC Toolset version N:
$ yum list available gcc-toolset-N-\*
2. To install any of these packages:
# yum install package_name
Replace package_name with a space-separated list of packages to install. For example, to install
the gcc-toolset-9-gdb-gdbserver and gcc-toolset-9-gdb-doc packages:
# yum install gcc-toolset-9-gdb-gdbserver gcc-toolset-9-gdb-doc
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4.1.4. Uninstalling GCC Toolset
To remove GCC Toolset from your system, uninstall it using the yum package management tool.
Procedure
To uninstall GCC Toolset version N:
# yum remove gcc-toolset-N\*
4.1.5. Running a tool from GCC Toolset
To run a tool from GCC Toolset, use the scl utility.
Procedure
To run a tool from GCC Toolset version N:
$ scl enable gcc-toolset-N tool
4.1.6. Running a shell session with GCC Toolset
GCC Toolset allows running a shell session where the GCC Toolset tool versions are used instead of
system versions of these tools, without explicitly using the scl command. This is useful when you need to
interactively start the tools many times, such as when setting up or testing a development setup.
Procedure
To run a shell session where tool versions from GCC Toolset version N override system versions
of these tools:
$ scl enable gcc-toolset-N bash
4.1.7. Additional resources
Red Hat Developer Toolset User Guide
4.2. GCC TOOLSET 9
Learn about information specific to GCC Toolset version 9 and the tools contained in this version.
4.2.1. Tools and versions provided by GCC Toolset 9
GCC Toolset 9 provides the following tools and versions:
Table 4.1. Tool versions in GCC Toolset 9
Name Version Description
GCC 9.2.1 A portable compiler suite with support for C, C++, and Fortran.
CHAPTER 4. ADDITIONAL TOOLSETS FOR DEVELOPMENT
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GDB 8.3 A command-line debugger for programs written in C, C++, and Fortran.
Valgrind 3.15.0 An instrumentation framework and a number of tools to profile
applications in order to detect memory errors, identify memory
management problems, and report any use of improper arguments in
system calls.
SystemTap 4.1 A tracing and probing tool to monitor the activities of the entire system
without the need to instrument, recompile, install, and reboot.
Dyninst 10.1.0 A library for instrumenting and working with user-space executables
during their execution.
binutils 2.32 A collection of binary tools and other utilities to inspect and manipulate
object files and binaries.
elfutils 0.176 A collection of binary tools and other utilities to inspect and manipulate
ELF files.
dwz 0.12 A tool to optimize DWARF debugging information contained in ELF
shared libraries and ELF executables for size.
make 4.2.1 A dependency-tracking build automation tool.
strace 5.1 A debugging tool to monitor system calls that a program uses and
signals it receives.
ltrace 0.7.91 A debugging tool to display calls to dynamic libraries that a program
makes. It can also monitor system calls executed by programs.
annobin 9.08 A build security checking tool.
Name Version Description
4.2.2. C++ compatibility in GCC Toolset 9
IMPORTANT
The compatibility information presented here apply only to the GCC from GCC Toolset
9.
The GCC compiler in GCC Toolset can use the following C++ standards:
C++14
This is the default language standard setting for GCC Toolset 9, with GNU extensions, equivalent to
explicitly using option -std=gnu++14.
Using the C++14 language version is supported when all C++ objects compiled with the respective
flag have been built using GCC version 6 or later.
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C++11
This language standard is available in GCC Toolset 9.
Using the C++11 language version is supported when all C++ objects compiled with the respective flag
have been built using GCC version 5 or later.
C++98
This language standard is available in GCC Toolset 9. Binaries, shared libraries and objects built using
this standard can be freely mixed regardless of being built with GCC from GCC Toolset, Red Hat
Developer Toolset, and RHEL 5, 6, 7 and 8.
C++17, C++2a
These language standards are available in GCC Toolset 9 only as an experimental, unstable, and
unsupported capability. Additionally, compatibility of objects, binary files, and libraries built using
these standards cannot be guaranteed.
All of the language standards are available in both the standard compliant variant or with GNU
extensions.
When mixing objects built with GCC Toolset with those built with the RHEL toolchain (particularly .o or
.a files), GCC Toolset toolchain should be used for any linkage. This ensures any newer library features
provided only by GCC Toolset are resolved at link time.
4.2.3. Specifics of GCC in GCC Toolset 9
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-9 'gcc -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-9 'gcc objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
CHAPTER 4. ADDITIONAL TOOLSETS FOR DEVELOPMENT
71
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
GCC.
4.2.4. Specifics of binutils in GCC Toolset 9
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-9 'ld -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-9 'ld objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
binutils.
4.3. GCC TOOLSET 10
Learn about information specific to GCC Toolset version 10 and the tools contained in this version.
4.3.1. Tools and versions provided by GCC Toolset 10
GCC Toolset 10 provides the following tools and versions:
Table 4.2. Tool versions in GCC Toolset 10
Name Version Description
GCC 10.2.1 A portable compiler suite with support for C, C++, and Fortran.
GDB 9.2 A command-line debugger for programs written in C, C++, and Fortran.
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Valgrind 3.16.0 An instrumentation framework and a number of tools to profile
applications in order to detect memory errors, identify memory
management problems, and report any use of improper arguments in
system calls.
SystemTap 4.4 A tracing and probing tool to monitor the activities of the entire system
without the need to instrument, recompile, install, and reboot.
Dyninst 10.2.1 A library for instrumenting and working with user-space executables
during their execution.
binutils 2.35 A collection of binary tools and other utilities to inspect and manipulate
object files and binaries.
elfutils 0.182 A collection of binary tools and other utilities to inspect and manipulate
ELF files.
dwz 0.12 A tool to optimize DWARF debugging information contained in ELF
shared libraries and ELF executables for size.
make 4.2.1 A dependency-tracking build automation tool.
strace 5.7 A debugging tool to monitor system calls that a program uses and
signals it receives.
ltrace 0.7.91 A debugging tool to display calls to dynamic libraries that a program
makes. It can also monitor system calls executed by programs.
annobin 9.29 A build security checking tool.
Name Version Description
4.3.2. C++ compatibility in GCC Toolset 10
IMPORTANT
The compatibility information presented here apply only to the GCC from GCC Toolset
10.
The GCC compiler in GCC Toolset can use the following C++ standards:
C++14
This is the default language standard setting for GCC Toolset 10, with GNU extensions, equivalent
to explicitly using option -std=gnu++14.
Using the C++14 language version is supported when all C++ objects compiled with the respective
flag have been built using GCC version 6 or later.
C++11
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73
This language standard is available in GCC Toolset 10.
Using the C++11 language version is supported when all C++ objects compiled with the respective flag
have been built using GCC version 5 or later.
C++98
This language standard is available in GCC Toolset 10. Binaries, shared libraries and objects built
using this standard can be freely mixed regardless of being built with GCC from GCC Toolset, Red
Hat Developer Toolset, and RHEL 5, 6, 7 and 8.
C++17
This language standard is available in GCC Toolset 10.
C++20
This language standard is available in GCC Toolset 10 only as an experimental, unstable, and
unsupported capability. Additionally, compatibility of objects, binary files, and libraries built using this
standard cannot be guaranteed.
All of the language standards are available in both the standard compliant variant or with GNU
extensions.
When mixing objects built with GCC Toolset with those built with the RHEL toolchain (particularly .o or
.a files), GCC Toolset toolchain should be used for any linkage. This ensures any newer library features
provided only by GCC Toolset are resolved at link time.
4.3.3. Specifics of GCC in GCC Toolset 10
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-10 'gcc -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-10 'gcc objfile.o -lsomelib'
Red Hat Enterprise Linux 8 Developing C and C++ applications in RHEL 8
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Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
GCC.
4.3.4. Specifics of binutils in GCC Toolset 10
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-10 'ld -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-10 'ld objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
binutils.
4.4. GCC TOOLSET 11
Learn about information specific to GCC Toolset version 11 and the tools contained in this version.
4.4.1. Tools and versions provided by GCC Toolset 11
GCC Toolset 11 provides the following tools and versions:
Table 4.3. Tool versions in GCC Toolset 11
Name Version Description
GCC 11.2.1 A portable compiler suite with support for C, C++, and Fortran.
GDB 10.2 A command-line debugger for programs written in C, C++, and Fortran.
CHAPTER 4. ADDITIONAL TOOLSETS FOR DEVELOPMENT
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Valgrind 3.17.0 An instrumentation framework and a number of tools to profile
applications in order to detect memory errors, identify memory
management problems, and report any use of improper arguments in
system calls.
SystemTap 4.5 A tracing and probing tool to monitor the activities of the entire system
without the need to instrument, recompile, install, and reboot.
Dyninst 11.0.0 A library for instrumenting and working with user-space executables
during their execution.
binutils 2.36.1 A collection of binary tools and other utilities to inspect and manipulate
object files and binaries.
elfutils 0.185 A collection of binary tools and other utilities to inspect and manipulate
ELF files.
dwz 0.14 A tool to optimize DWARF debugging information contained in ELF
shared libraries and ELF executables for size.
make 4.3 A dependency-tracking build automation tool.
strace 5.13 A debugging tool to monitor system calls that a program uses and
signals it receives.
ltrace 0.7.91 A debugging tool to display calls to dynamic libraries that a program
makes. It can also monitor system calls executed by programs.
annobin 10.23 A build security checking tool.
Name Version Description
4.4.2. C++ compatibility in GCC Toolset 11
IMPORTANT
The compatibility information presented here apply only to the GCC from GCC Toolset
11.
The GCC compiler in GCC Toolset can use the following C++ standards:
C++14
This language standard is available in GCC Toolset 11.
Using the C++14 language version is supported when all C++ objects compiled with the respective
flag have been built using GCC version 6 or later.
C++11
This language standard is available in GCC Toolset 11.
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Using the C++11 language version is supported when all C++ objects compiled with the respective flag
have been built using GCC version 5 or later.
C++98
This language standard is available in GCC Toolset 11. Binaries, shared libraries and objects built using
this standard can be freely mixed regardless of being built with GCC from GCC Toolset, Red Hat
Developer Toolset, and RHEL 5, 6, 7 and 8.
C++17
This language standard is available in GCC Toolset 11.
This is the default language standard setting for GCC Toolset 11, with GNU extensions, equivalent to
explicitly using option -std=gnu++17.
Using the C++17 language version is supported when all C++ objects compiled with the respective
flag have been built using GCC version 10 or later.
C++20 and C++23
This language standard is available in GCC Toolset 11 only as an experimental, unstable, and
unsupported capability. Additionally, compatibility of objects, binary files, and libraries built using this
standard cannot be guaranteed.
To enable C++20 support, add the command-line option -std=c++20 to your g++ command line.
To enable C++23 support, add the command-line option -std=c++2b to your g++ command line.
All of the language standards are available in both the standard compliant variant or with GNU
extensions.
When mixing objects built with GCC Toolset with those built with the RHEL toolchain (particularly .o or
.a files), GCC Toolset toolchain should be used for any linkage. This ensures any newer library features
provided only by GCC Toolset are resolved at link time.
4.4.3. Specifics of GCC in GCC Toolset 11
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
CHAPTER 4. ADDITIONAL TOOLSETS FOR DEVELOPMENT
77
$ scl enable gcc-toolset-11 'gcc -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-11 'gcc objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
GCC.
4.4.4. Specifics of binutils in GCC Toolset 11
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-11 'ld -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-11 'ld objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
binutils.
4.5. GCC TOOLSET 12
Learn about information specific to GCC Toolset version 12 and the tools contained in this version.
4.5.1. Tools and versions provided by GCC Toolset 12
GCC Toolset 12 provides the following tools and versions:
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Table 4.4. Tool versions in GCC Toolset 12
Name Version Description
GCC 12.2.1 A portable compiler suite with support for C, C++, and Fortran.
GDB 11.2 A command-line debugger for programs written in C, C++, and Fortran.
binutils 2.38 A collection of binary tools and other utilities to inspect and manipulate
object files and binaries.
dwz 0.14 A tool to optimize DWARF debugging information contained in ELF
shared libraries and ELF executables for size.
annobin 11.08 A build security checking tool.
4.5.2. C++ compatibility in GCC Toolset 12
IMPORTANT
The compatibility information presented here apply only to the GCC from GCC Toolset
12.
The GCC compiler in GCC Toolset can use the following C++ standards:
C++14
This language standard is available in GCC Toolset 12.
Using the C++14 language version is supported when all C++ objects compiled with the respective
flag have been built using GCC version 6 or later.
C++11
This language standard is available in GCC Toolset 12.
Using the C++11 language version is supported when all C++ objects compiled with the respective flag
have been built using GCC version 5 or later.
C++98
This language standard is available in GCC Toolset 12. Binaries, shared libraries and objects built
using this standard can be freely mixed regardless of being built with GCC from GCC Toolset, Red
Hat Developer Toolset, and RHEL 5, 6, 7 and 8.
C++17
This language standard is available in GCC Toolset 12.
This is the default language standard setting for GCC Toolset 12, with GNU extensions, equivalent to
explicitly using option -std=gnu++17.
Using the C++17 language version is supported when all C++ objects compiled with the respective
flag have been built using GCC version 10 or later.
C++20 and C++23
This language standard is available in GCC Toolset 12 only as an experimental, unstable, and
CHAPTER 4. ADDITIONAL TOOLSETS FOR DEVELOPMENT
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This language standard is available in GCC Toolset 12 only as an experimental, unstable, and
unsupported capability. Additionally, compatibility of objects, binary files, and libraries built using this
standard cannot be guaranteed.
To enable C++20 support, add the command-line option -std=c++20 to your g++ command line.
To enable C++23 support, add the command-line option -std=c++23 to your g++ command line.
All of the language standards are available in both the standard compliant variant or with GNU
extensions.
When mixing objects built with GCC Toolset with those built with the RHEL toolchain (particularly .o or
.a files), GCC Toolset toolchain should be used for any linkage. This ensures any newer library features
provided only by GCC Toolset are resolved at link time.
4.5.3. Specifics of GCC in GCC Toolset 12
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-12 'gcc -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-12 'gcc objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
GCC.
4.5.4. Specifics of binutils in GCC Toolset 12
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
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security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-12 'ld -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-12 'ld objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
binutils.
4.5.5. Specifics of annobin in GCC Toolset 12
Under some circumstances, due to a synchronization issue between annobin and gcc in GCC Toolset 12,
your compilation can fail with an error message that looks similar to the following:
cc1: fatal error: inaccessible plugin file
opt/rh/gcc-toolset-12/root/usr/lib/gcc/architecture-linux-gnu/12/plugin/gcc-annobin.so
expanded from short plugin name gcc-annobin: No such file or directory
To work around the problem, create a symbolic link in the plugin directory from the annobin.so file to
the gcc-annobin.so file:
# cd /opt/rh/gcc-toolset-12/root/usr/lib/gcc/architecture-linux-gnu/12/plugin
# ln -s annobin.so gcc-annobin.so
Replace architecture with the architecture you use in your system:
aarch64
i686
ppc64le
s390x
x86_64
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4.6. GCC TOOLSET 13
Learn about information specific to GCC Toolset version 13 and the tools contained in this version.
4.6.1. Tools and versions provided by GCC Toolset 13
GCC Toolset 13 provides the following tools and versions:
Table 4.5. Tool versions in GCC Toolset 13
Name Version Description
GCC 13.2.1 A portable compiler suite with support for C, C++, and Fortran.
GDB 12.1 A command-line debugger for programs written in C, C++, and Fortran.
binutils 2.40 A collection of binary tools and other utilities to inspect and manipulate
object files and binaries.
dwz 0.14 A tool to optimize DWARF debugging information contained in ELF
shared libraries and ELF executables for size.
annobin 12.32 A build security checking tool.
4.6.2. C++ compatibility in GCC Toolset 13
IMPORTANT
The compatibility information presented here apply only to the GCC from GCC Toolset
13.
The GCC compiler in GCC Toolset can use the following C++ standards:
C++14
This language standard is available in GCC Toolset 13.
Using the C++14 language version is supported when all C++ objects compiled with the respective
flag have been built using GCC version 6 or later.
C++11
This language standard is available in GCC Toolset 13.
Using the C++11 language version is supported when all C++ objects compiled with the respective flag
have been built using GCC version 5 or later.
C++98
This language standard is available in GCC Toolset 13. Binaries, shared libraries and objects built
using this standard can be freely mixed regardless of being built with GCC from GCC Toolset, Red
Hat Developer Toolset, and RHEL 5, 6, 7 and 8.
C++17
This language standard is available in GCC Toolset 13.
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This is the default language standard setting for GCC Toolset 13, with GNU extensions, equivalent to
explicitly using option -std=gnu++17.
Using the C++17 language version is supported when all C++ objects compiled with the respective
flag have been built using GCC version 10 or later.
C++20 and C++23
These language standards are available in GCC Toolset 13 only as an experimental, unstable, and
unsupported capability. Additionally, compatibility of objects, binary files, and libraries built using this
standard cannot be guaranteed.
To enable the C++20 standard, add the command-line option -std=c++20 to your g++ command line.
To enable the C++23 standard, add the command-line option -std=c++23 to your g++ command line.
All of the language standards are available in both the standard compliant variant or with GNU
extensions.
When mixing objects built with GCC Toolset with those built with the RHEL toolchain (particularly .o or
.a files), GCC Toolset toolchain should be used for any linkage. This ensures any newer library features
provided only by GCC Toolset are resolved at link time.
4.6.3. Specifics of GCC in GCC Toolset 13
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-13 'gcc -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-13 'gcc objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
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Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
GCC.
4.6.4. Specifics of binutils in GCC Toolset 13
Static linking of libraries
Certain more recent library features are statically linked into applications built with GCC Toolset to
support execution on multiple versions of Red Hat Enterprise Linux. This creates an additional minor
security risk because standard Red Hat Enterprise Linux errata do not change this code. If the need
arises for developers to rebuild their applications due to this risk, Red Hat will communicate this using a
security erratum.
IMPORTANT
Because of this additional security risk, developers are strongly advised not to statically
link their entire application for the same reasons.
Specify libraries after object files when linking
In GCC Toolset, libraries are linked using linker scripts which might specify some symbols through static
archives. This is required to ensure compatibility with multiple versions of Red Hat Enterprise Linux.
However, the linker scripts use the names of the respective shared object files. As a consequence, the
linker uses different symbol handling rules than expected, and does not recognize symbols required by
object files when the option adding the library is specified before options specifying the object files:
$ scl enable gcc-toolset-13 'ld -lsomelib objfile.o'
Using a library from GCC Toolset in this manner results in the linker error message undefined reference
to symbol. To prevent this problem, follow the standard linking practice, and specify the option adding
the library after the options specifying the object files:
$ scl enable gcc-toolset-13 'ld objfile.o -lsomelib'
Note that this recommendation also applies when using the base Red Hat Enterprise Linux version of
binutils.
4.6.5. Specifics of annobin in GCC Toolset 13
Under some circumstances, due to a synchronization issue between annobin and gcc in GCC Toolset 13,
your compilation can fail with an error message that looks similar to the following:
cc1: fatal error: inaccessible plugin file
opt/rh/gcc-toolset-13/root/usr/lib/gcc/architecture-linux-gnu/13/plugin/gcc-annobin.so
expanded from short plugin name gcc-annobin: No such file or directory
To work around the problem, create a symbolic link in the plugin directory from the annobin.so file to
the gcc-annobin.so file:
# cd /opt/rh/gcc-toolset-13/root/usr/lib/gcc/architecture-linux-gnu/13/plugin
# ln -s annobin.so gcc-annobin.so
Replace architecture with the architecture you use in your system:
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aarch64
i686
ppc64le
s390x
x86_64
4.7. USING THE GCC TOOLSET CONTAINER IMAGE
Only the GCC Toolset 13 container image is supported. Container images of earlier GCC Toolset
versions are deprecated.
The GCC Toolset 13 components are available in the GCC Toolset 13 Toolchain container image.
The GCC Toolset container image is based on the rhel8 base image and is available for all architectures
supported by RHEL 8:
AMD and Intel 64-bit architectures
The 64-bit ARM architecture
IBM Power Systems, Little Endian
64-bit IBM Z
4.7.1. GCC Toolset container image contents
Tools versions provided in the GCC Toolset 13 container image match the GCC Toolset 13 components
versions.
The GCC Toolset 13 Toolchain contents
The rhel8/gcc-toolset-13-toolchain image provides the GCC compiler, the GDB debugger, and other
development-related tools. The container image consists of the following components:
Component Package
gcc gcc-toolset-13-gcc
g++ gcc-toolset-13-gcc-c++
gfortran gcc-toolset-13-gcc-gfortran
gdb gcc-toolset-13-gdb
4.7.2. Accessing and running the GCC Toolset container image
The following section describes how to access and run the GCC Toolset container image.
Prerequisites
CHAPTER 4. ADDITIONAL TOOLSETS FOR DEVELOPMENT
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Podman is installed.
Procedure
1. Access the Red Hat Container Registry using your Customer Portal credentials:
$ podman login registry.redhat.io
Username: username
Password: ********
2. Pull the container image you require by running a relevant command as root:
# podman pull registry.redhat.io/rhel8/gcc-toolset-13-toolchain
NOTE
On RHEL 8.1 and later versions, you can set up your system to work with
containers as a non-root user. For details, see Setting up rootless containers.
3. Optional: Check that pulling was successful by running a command that lists all container images
on your local system:
# podman images
4. Run a container by launching a bash shell inside a container:
# podman run -it image_name /bin/bash
The -i option creates an interactive session; without this option the shell opens and instantly
exits.
The -t option opens a terminal session; without this option you cannot type anything to the shell.
Additional resources
Building, running, and managing Linux containers on RHEL 8
A Red Hat blog article — Understanding root inside and outside a container
Entries in the Red Hat Container Registry — GCC Toolset container images
4.7.3. Example: Using the GCC Toolset 13 Toolchain container image
This example shows how to pull and start using the GCC Toolset 13 Toolchain container image.
Prerequisites
Podman is installed.
Procedure
1. Access the Red Hat Container Registry using your Customer Portal credentials:
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$ podman login registry.redhat.io
Username: username
Password: ********
2. Pull the container image as root:
# podman pull registry.redhat.io/rhel8/gcc-toolset-13-toolchain
3. Launch the container image with an interactive shell as root:
# podman run -it registry.redhat.io/rhel8/gcc-toolset-13-toolchain /bin/bash
4. Run the GCC Toolset tools as expected. For example, to verify the gcc compiler version, run:
bash-4.4$ gcc -v
...
gcc version 13.1.1 20231102 (Red Hat 13.1.1-4) (GCC)
5. To list all packages provided in the container, run:
bash-4.4$ rpm -qa
4.8. COMPILER TOOLSETS
RHEL 8 provides the following compiler toolsets as Application Streams:
LLVM Toolset provides the LLVM compiler infrastructure framework, the Clang compiler for
the C and C++ languages, the LLDB debugger, and related tools for code analysis.
Rust Toolset provides the Rust programming language compiler rustc, the cargo build tool and
dependency manager, the cargo-vendor plugin, and required libraries.
Go Toolset provides the Go programming language tools and libraries. Go is alternatively
known as golang.
For more details and information about usage, see the compiler toolsets user guides on the Red Hat
Developer Tools page.
4.9. THE ANNOBIN PROJECT
The Annobin project is an implementation of the Watermark specification project. Watermark
specification project intends to add markers to Executable and Linkable Format (ELF) objects to
determine their properties. The Annobin project consists of the annobin plugin and the annockeck
program.
The annobin plugin scans the GNU Compiler Collection (GCC) command line, the compilation state,
and the compilation process, and generates the ELF notes. The ELF notes record how the binary was
built and provide information for the annocheck program to perform security hardening checks.
The security hardening checker is part of the annocheck program and is enabled by default. It checks
the binary files to determine whether the program was built with necessary security hardening options
and compiled correctly. annocheck is able to recursively scan directories, archives, and RPM packages
for ELF object files.
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87
NOTE
The files must be in ELF format. annocheck does not handle any other binary file types.
The following section describes how to:
Use the annobin plugin
Use the annocheck program
Remove redundant annobin notes
4.9.1. Using the annobin plugin
The following section describes how to:
Enable the annobin plugin
Pass options to the annobin plugin
4.9.1.1. Enabling the annobin plugin
The following section describes how to enable the annobin plugin via gcc and via clang.
Procedure
To enable the annobin plugin with gcc, use:
$ gcc -fplugin=annobin
If gcc does not find the annobin plugin, use:
$ gcc -iplugindir=/path/to/directory/containing/annobin/
Replace /path/to/directory/containing/annobin/ with the absolute path to the directory
that contains annobin.
To find the directory containing the annobin plugin, use:
$ gcc --print-file-name=plugin
To enable the annobin plugin with clang, use:
$ clang -fplugin=/path/to/directory/containing/annobin/
Replace /path/to/directory/containing/annobin/ with the absolute path to the directory that
contains annobin.
4.9.1.2. Passing options to the annobin plugin
The following section describes how to pass options to the annobin plugin via gcc and via clang.
Procedure
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To pass options to the annobin plugin with gcc, use:
$ gcc -fplugin=annobin -fplugin-arg-annobin-option file-name
Replace option with the annobin command line arguments and replace file-name with the
name of the file.
Example
To display additional details about what annobin it is doing, use:
$ gcc -fplugin=annobin -fplugin-arg-annobin-verbose file-name
Replace file-name with the name of the file.
To pass options to the annobin plugin with clang, use:
$ clang -fplugin=/path/to/directory/containing/annobin/ -Xclang -plugin-arg-annobin -Xclang
option file-name
Replace option with the annobin command line arguments and replace
/path/to/directory/containing/annobin/ with the absolute path to the directory containing
annobin.
Example
To display additional details about what annobin it is doing, use:
$ clang -fplugin=/usr/lib64/clang/10/lib/annobin.so -Xclang -plugin-arg-annobin -Xclang
verbose file-name
Replace file-name with the name of the file.
4.9.2. Using the annocheck program
The following section describes how to use annocheck to examine:
Files
Directories
RPM packages
annocheck extra tools
NOTE
annocheck recursively scans directories, archives, and RPM packages for ELF object
files. The files have to be in the ELF format. annocheck does not handle any other binary
file types.
4.9.2.1. Using annocheck to examine files
The following section describes how to examine ELF files using annocheck.
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Procedure
To examine a file, use:
$ annocheck file-name
Replace file-name with the name of a file.
NOTE
The files must be in ELF format. annocheck does not handle any other binary file types.
annocheck processes static libraries that contain ELF object files.
Additional information
For more information about annocheck and possible command line options, see the
annocheck man page.
4.9.2.2. Using annocheck to examine directories
The following section describes how to examine ELF files in a directory using annocheck.
Procedure
To scan a directory, use:
$ annocheck directory-name
Replace directory-name with the name of a directory. annocheck automatically examines the
contents of the directory, its sub-directories, and any archives and RPM packages within the
directory.
NOTE
annocheck only looks for ELF files. Other file types are ignored.
Additional information
For more information about annocheck and possible command line options, see the
annocheck man page.
4.9.2.3. Using annocheck to examine RPM packages
The following section describes how to examine ELF files in an RPM package using annocheck.
Procedure
To scan an RPM package, use:
$ annocheck rpm-package-name
Replace rpm-package-name with the name of an RPM package. annocheck recursively scans all
the ELF files inside the RPM package.
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NOTE
annocheck only looks for ELF files. Other file types are ignored.
To scan an RPM package with provided debug info RPM, use:
$ annocheck rpm-package-name --debug-rpm debuginfo-rpm
Replace rpm-package-name with the name of an RPM package, and debuginfo-rpm with the
name of a debug info RPM associated with the binary RPM.
Additional information
For more information about annocheck and possible command line options, see the
annocheck man page.
4.9.2.4. Using annocheck extra tools
annocheck includes multiple tools for examining binary files. You can enable these tools with the
command-line options.
The following section describes how to enable the:
built-by tool
notes tool
section-size tool
You can enable multiple tools at the same time.
NOTE
The hardening checker is enabled by default.
4.9.2.4.1. Enabling the built-by tool
You can use the annocheck built-by tool to find the name of the compiler that built the binary file.
Procedure
To enable the built-by tool, use:
$ annocheck --enable-built-by
Additional information
For more information about the built-by tool, see the --help command-line option.
4.9.2.4.2. Enabling the notes tool
You can use the annocheck notes tool to display the notes stored inside a binary file created by the
annobin plugin.
Procedure
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Procedure
To enable the notes tool, use:
$ annocheck --enable-notes
The notes are displayed in a sequence sorted by the address range.
Additional information
For more information about the notes tool, see the --help command-line option.
4.9.2.4.3. Enabling the section-size tool
You can use the annocheck section-size tool display the size of the named sections.
Procedure
To enable the section-size tool, use:
$ annocheck --section-size=name
Replace name with the name of the named section. The output is restricted to specific sections.
A cumulative result is produced at the end.
Additional information
For more information about the section-size tool, see the --help command-line option.
4.9.2.4.4. Hardening checker basics
The hardening checker is enabled by default. You can disable the hardening checker with the --disable-
hardened command-line option.
4.9.2.4.4.1. Hardening checker options
The annocheck program checks the following options:
Lazy binding is disabled using the -z now linker option.
The program does not have a stack in an executable region of memory.
The relocations for the GOT table are set to read only.
No program segment has all three of the read, write and execute permission bits set.
There are no relocations against executable code.
The runpath information for locating shared libraries at runtime includes only directories rooted
at /usr.
The program was compiled with annobin notes enabled.
The program was compiled with the -fstack-protector-strong option enabled.
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The program was compiled with -D_FORTIFY_SOURCE=2.
The program was compiled with -D_GLIBCXX_ASSERTIONS.
The program was compiled with -fexceptions enabled.
The program was compiled with -fstack-clash-protection enabled.
The program was compiled at -O2 or higher.
The program does not have any relocations held in a writeable.
Dynamic executables have a dynamic segment.
Shared libraries were compiled with -fPIC or -fPIE.
Dynamic executables were compiled with -fPIE and linked with -pie.
If available, the -fcf-protection=full option was used.
If available, the -mbranch-protection option was used.
If available, the -mstackrealign option was used.
4.9.2.4.4.2. Disabling the hardening checker
The following section describes how to disable the hardening checker.
Procedure
To scan the notes in a file without the hardening checker, use:
$ annocheck --enable-notes --disable-hardened file-name
Replace file-name with the name of a file.
4.9.3. Removing redundant annobin notes
Using annobin increases the size of binaries. To reduce the size of the binaries compiled with annobin
you can remove redundant annobin notes. To remove the redundant annobin notes use the objcopy
program, which is a part of the binutils package.
Procedure
To remove the redundant annobin notes, use:
$ objcopy --merge-notes file-name
Replace file-name with the name of the file.
4.9.4. Specifics of annobin in GCC Toolset 12
Under some circumstances, due to a synchronization issue between annobin and gcc in GCC Toolset 12,
your compilation can fail with an error message that looks similar to the following:
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93
cc1: fatal error: inaccessible plugin file
opt/rh/gcc-toolset-12/root/usr/lib/gcc/architecture-linux-gnu/12/plugin/gcc-annobin.so
expanded from short plugin name gcc-annobin: No such file or directory
To work around the problem, create a symbolic link in the plugin directory from the annobin.so file to
the gcc-annobin.so file:
# cd /opt/rh/gcc-toolset-12/root/usr/lib/gcc/architecture-linux-gnu/12/plugin
# ln -s annobin.so gcc-annobin.so
Replace architecture with the architecture you use in your system:
aarch64
i686
ppc64le
s390x
x86_64
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CHAPTER 5. SUPPLEMENTARY TOPICS
5.1. COMPATIBILITY-BREAKING CHANGES IN COMPILERS AND
DEVELOPMENT TOOLS
librtkaio removed
With this update, the librtkaio library has been removed. This library provided high-performance real-
time asynchronous I/O access for some files, which was based on Linux kernel Asynchronous I/O
support (KAIO).
As a result of the removal:
Applications using the LD_PRELOAD method to load librtkaio display a warning about a
missing library, load the librt library instead and run correctly.
Applications using the LD_LIBRARY_PATH method to load librtkaio load the librt library
instead and run correctly, without any warning.
Applications using the dlopen() system call to access librtkaio directly load the librt library
instead.
Users of librtkaio have the following options:
Use the fallback mechanism described above, without any changes to their applications.
Change code of their applications to use the librt library, which offers a compatible POSIX-
compliant API.
Change code of their applications to use the libaio library, which offers a compatible API.
Both librt and libaio can provide comparable features and performance under specific conditions.
Note that the libaio package has Red Hat compatibility level of 2, while librtk and the removed librtkaio
level 1.
For more details, see https://fedoraproject.org/wiki/Changes/GLIBC223_librtkaio_removal
Sun RPC and NIS interfaces removed from glibc
The glibc library no longer provides Sun RPC and NIS interfaces for new applications. These interfaces
are now available only for running legacy applications. Developers must change their applications to use
the libtirpc library instead of Sun RPC and libnsl2 instead of NIS. Applications can benefit from IPv6
support in the replacement libraries.
The nosegneg libraries for 32-bit Xen have been removed
Previously, the glibc i686 packages contained an alternative glibc build, which avoided the use of the
thread descriptor segment register with negative offsets (nosegneg). This alternative build was only
used in the 32-bit version of the Xen Project hypervisor without hardware virtualization support, as an
optimization to reduce the cost of full paravirtualization. These alternative builds are no longer used and
they have been removed.
make new operator != causes a different interpretation of certain existing makefile syntax
The != shell assignment operator has been added to GNU make as an alternative to the $(shell …)
function to increase compatibility with BSD makefiles. As a consequence, variables with name ending in
exclamation mark and immediately followed by assignment such as variable!=value are now interpreted
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as the shell assignment. To restore the previous behavior, add a space after the exclamation mark, such
as variable! =value.
For more details and differences between the operator and the function, see the GNU make manual.
Valgrind library for MPI debugging support removed
The libmpiwrap.so wrapper library for Valgrind provided by the valgrind-openmpi package has been
removed. This library enabled Valgrind to debug programs using the Message Passing Interface (MPI).
This library was specific to the Open MPI implementation version in previous versions of Red Hat
Enterprise Linux.
Users of libmpiwrap.so are encouraged to build their own version from upstream sources specific to
their MPI implementation and version. Supply these custom-built libraries to Valgrind using the
LD_PRELOAD technique.
Development headers and static libraries removed from valgrind-devel
Previously, the valgrind-devel sub-package used to include development files for developing custom
valgrind tools. This update removes these files because they do not have a guaranteed API, have to be
linked statically, and are unsupported. The valgrind-devel package still does contain the development
files for valgrind-aware programs and header files such as valgrind.h, callgrind.h, drd.h, helgrind.h,
and memcheck.h, which are stable and well-supported.
5.2. OPTIONS FOR RUNNING A RHEL 6 OR 7 APPLICATION ON RHEL 8
To run a Red Hat Enterprise Linux 6 or 7 application on Red Hat Enterprise Linux 8, a spectrum of
options is available. A system administrator needs detailed guidance from the application developer. The
following list outlines the options, considerations, and resources provided by Red Hat.
Run the application in a virtual machine with a matching RHEL version guest OS
Resource costs are high for this option, but the environment is a close match to the application’s
requirements, and this approach does not require many additional considerations. This is the
currently recommended option.
Run the application in a container based on the respective RHEL version
Resource costs are lower than in the previous cases, while configuration requirements are stricter.
For details on the relationship between container hosts and guest user spaces, see the Red Hat
Enterprise Linux Container Compatibility Matrix.
Run the application natively on RHEL 8
This option offers the lowest resource costs, but also the most strict requirements. The application
developer must determine a correct configuration of the RHEL 8 system. The following resources
can help the developer in this task:
Red Hat Enterprise Linux 8: Application Compatibility Guide
Red Hat Enterprise Linux 7: Application Compatibility Guide
Release notes for Red Hat Enterprise Linux 8.0
Considerations in adopting RHEL 8
Note that this list is not a complete set of resources needed to determine application compatibility.
These are only starting points with lists of known incompatible changes and Red Hat policies related
to compatibility.
Additionally, the What is Kernel Application Binary Interface (kABI)? Knowledge Centered Support
Red Hat Enterprise Linux 8 Developing C and C++ applications in RHEL 8
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