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diff --git a/Documentation/kbuild/gcc-plugins.rst b/Documentation/kbuild/gcc-plugins.rst new file mode 100644 index 000000000..c578c6ba3 --- /dev/null +++ b/Documentation/kbuild/gcc-plugins.rst @@ -0,0 +1,133 @@ +========================= +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]_. + +-- + +.. [1] https://gcc.gnu.org/onlinedocs/gccint/Plugins.html +.. [2] https://gcc.gnu.org/onlinedocs/gccint/Plugin-API.html#Plugin-API +.. [3] https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html +.. [4] https://gcc.gnu.org/onlinedocs/gccint/IPA.html +.. [5] https://gcc.gnu.org/onlinedocs/gccint/RTL.html +.. [6] https://grsecurity.net/ +.. [7] https://pax.grsecurity.net/ + + +Purpose +======= + +GCC plugins are designed to provide a place to experiment with potential +compiler features that are neither in GCC nor Clang upstream. Once +their utility is proven, the goal is to upstream the feature into GCC +(and Clang), and then to finally remove them from the kernel once the +feature is available in all supported versions of GCC. + +Specifically, new plugins should implement only features that have no +upstream compiler support (in either GCC or Clang). + +When a feature exists in Clang but not GCC, effort should be made to +bring the feature to upstream GCC (rather than just as a kernel-specific +GCC plugin), so the entire ecosystem can benefit from it. + +Similarly, even if a feature provided by a GCC plugin does *not* exist +in Clang, but the feature is proven to be useful, effort should be spent +to upstream the feature to GCC (and Clang). + +After a feature is available in upstream GCC, the plugin will be made +unbuildable for the corresponding GCC version (and later). Once all +kernel-supported versions of GCC provide the feature, the plugin will +be removed from the kernel. + + +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_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. |