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Diffstat (limited to 'Documentation/kbuild/gcc-plugins.rst')
| -rw-r--r-- | Documentation/kbuild/gcc-plugins.rst | 92 |
1 files changed, 64 insertions, 28 deletions
diff --git a/Documentation/kbuild/gcc-plugins.rst b/Documentation/kbuild/gcc-plugins.rst index 4b1c10f88e30..c578c6ba3eb6 100644 --- a/Documentation/kbuild/gcc-plugins.rst +++ b/Documentation/kbuild/gcc-plugins.rst @@ -11,16 +11,13 @@ 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 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. +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 the x86, arm, arm64 and -powerpc architectures. +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]_. @@ -35,6 +32,32 @@ This infrastructure was ported from grsecurity [6]_ and PaX [7]_. .. [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 ===== @@ -47,20 +70,13 @@ Files 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. + GIMPLE, SIMPLE_IPA, IPA and RTL passes. They should be preferred to creating the structures by hand. @@ -68,21 +84,41 @@ Usage ===== You must install the gcc plugin headers for your gcc version, -e.g., on Ubuntu for gcc-4.9:: +e.g., on Ubuntu for gcc-10:: - apt-get install gcc-4.9-plugin-dev + apt-get install gcc-10-plugin-dev Or on Fedora:: - dnf install gcc-plugin-devel + 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 -Enable a GCC plugin based feature in the kernel config:: +A full path means they are detected:: - CONFIG_GCC_PLUGIN_CYC_COMPLEXITY = y + /usr/lib/gcc/x86_64-redhat-linux/12/plugin -To compile only the plugin(s):: +To compile the minimum tool set including the plugin(s):: - make gcc-plugins + make scripts or just run the kernel make and compile the whole kernel with the cyclomatic complexity GCC plugin. @@ -91,7 +127,7 @@ 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. +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. |