GCC plugin infrastructure ========================= 1. Introduction =============== GCC plugins are loadable modules that provide extra features to the compiler . They are useful for runtime instrumentation and static analysis. We can analyse, change and add further code during compilation via callbacks , GIMPLE , IPA  and RTL passes . The GCC plugin infrastructure of the kernel supports all gcc versions from 4.5 to 6.0, building out-of-tree modules, cross-compilation and building in a separate directory. Plugin source files have to be compilable by both a C and a C++ compiler as well because gcc versions 4.5 and 4.6 are compiled by a C compiler, gcc-4.7 can be compiled by a C or a C++ compiler, and versions 4.8+ can only be compiled by a C++ compiler. Currently the GCC plugin infrastructure supports only the x86, arm, arm64 and powerpc architectures. This infrastructure was ported from grsecurity  and PaX . --  https://gcc.gnu.org/onlinedocs/gccint/Plugins.html  https://gcc.gnu.org/onlinedocs/gccint/Plugin-API.html#Plugin-API  https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html  https://gcc.gnu.org/onlinedocs/gccint/IPA.html  https://gcc.gnu.org/onlinedocs/gccint/RTL.html  https://grsecurity.net/  https://pax.grsecurity.net/ 2. 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-plugin.sh This script checks the availability of the included headers in gcc-common.h and chooses the proper host compiler to build the plugins (gcc-4.7 can be built by either gcc or g++). $(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 support all gcc versions from 4.5 to 6.0. They should be preferred to creating the structures by hand. 3. Usage ======== You must install the gcc plugin headers for your gcc version, e.g., on Ubuntu for gcc-4.9: apt-get install gcc-4.9-plugin-dev Enable a GCC plugin based feature in the kernel config: CONFIG_GCC_PLUGIN_CYC_COMPLEXITY = y To compile only the plugin(s): make gcc-plugins 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 $(src)/scripts/gcc-plugins/. You can use a file or a directory here. It must be added to $(src)/scripts/gcc-plugins/Makefile, $(src)/scripts/Makefile.gcc-plugins and $(src)/arch/Kconfig. See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin.