GCC plugin infrastructure¶
Introduction¶
GCC plugins are loadable modules that provide extra features to the compiler 1. They are useful for runtime instrumentation and static analysis. We can analyse, change and add further code during compilation via callbacks 2, GIMPLE 3, IPA 4 and RTL passes 5.
The GCC plugin infrastructure of the kernel supports building out-of-tree modules, cross-compilation and building in a separate directory. Plugin source files have to be compilable by a C++ compiler.
Currently the GCC plugin infrastructure supports only some architectures. Grep “select HAVE_GCC_PLUGINS” to find out which architectures support GCC plugins.
This infrastructure was ported from grsecurity 6 and PaX 7.
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Files¶
$(src)/scripts/gcc-plugins
This is the directory of the GCC plugins.
$(src)/scripts/gcc-plugins/gcc-common.h
This is a compatibility header for GCC plugins. It should be always included instead of individual gcc headers.
$(src)/scripts/gcc-plugins/gcc-generate-gimple-pass.h, $(src)/scripts/gcc-plugins/gcc-generate-ipa-pass.h, $(src)/scripts/gcc-plugins/gcc-generate-simple_ipa-pass.h, $(src)/scripts/gcc-plugins/gcc-generate-rtl-pass.h
These headers automatically generate the registration structures for GIMPLE, SIMPLE_IPA, IPA and RTL passes. They should be preferred to creating the structures by hand.
Usage¶
You must install the gcc plugin headers for your gcc version, e.g., on Ubuntu for gcc-10:
apt-get install gcc-10-plugin-dev
Or on Fedora:
dnf install gcc-plugin-devel libmpc-devel
Or on Fedora when using cross-compilers that include plugins:
dnf install libmpc-devel
Enable the GCC plugin infrastructure and some plugin(s) you want to use in the kernel config:
CONFIG_GCC_PLUGINS=y
CONFIG_GCC_PLUGIN_CYC_COMPLEXITY=y
CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y
...
Run gcc (native or cross-compiler) to ensure plugin headers are detected:
gcc -print-file-name=plugin
CROSS_COMPILE=arm-linux-gnu- ${CROSS_COMPILE}gcc -print-file-name=plugin
The word “plugin” means they are not detected:
plugin
A full path means they are detected:
/usr/lib/gcc/x86_64-redhat-linux/12/plugin
To compile the minimum tool set including the plugin(s):
make scripts
or just run the kernel make and compile the whole kernel with the cyclomatic complexity GCC plugin.
4. How to add a new GCC plugin¶
The GCC plugins are in scripts/gcc-plugins/. You need to put plugin source files right under scripts/gcc-plugins/. Creating subdirectories is not supported. It must be added to scripts/gcc-plugins/Makefile, scripts/Makefile.gcc-plugins and a relevant Kconfig file. See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin.