134 lines
4.1 KiB
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134 lines
4.1 KiB
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=========================
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GCC plugin infrastructure
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=========================
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Introduction
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============
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GCC plugins are loadable modules that provide extra features to the
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compiler [1]_. They are useful for runtime instrumentation and static analysis.
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We can analyse, change and add further code during compilation via
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callbacks [2]_, GIMPLE [3]_, IPA [4]_ and RTL passes [5]_.
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The GCC plugin infrastructure of the kernel supports building out-of-tree
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modules, cross-compilation and building in a separate directory.
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Plugin source files have to be compilable by a C++ compiler.
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Currently the GCC plugin infrastructure supports only some architectures.
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Grep "select HAVE_GCC_PLUGINS" to find out which architectures support
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GCC plugins.
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This infrastructure was ported from grsecurity [6]_ and PaX [7]_.
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--
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.. [1] https://gcc.gnu.org/onlinedocs/gccint/Plugins.html
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.. [2] https://gcc.gnu.org/onlinedocs/gccint/Plugin-API.html#Plugin-API
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.. [3] https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html
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.. [4] https://gcc.gnu.org/onlinedocs/gccint/IPA.html
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.. [5] https://gcc.gnu.org/onlinedocs/gccint/RTL.html
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.. [6] https://grsecurity.net/
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.. [7] https://pax.grsecurity.net/
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Purpose
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=======
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GCC plugins are designed to provide a place to experiment with potential
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compiler features that are neither in GCC nor Clang upstream. Once
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their utility is proven, the goal is to upstream the feature into GCC
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(and Clang), and then to finally remove them from the kernel once the
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feature is available in all supported versions of GCC.
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Specifically, new plugins should implement only features that have no
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upstream compiler support (in either GCC or Clang).
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When a feature exists in Clang but not GCC, effort should be made to
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bring the feature to upstream GCC (rather than just as a kernel-specific
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GCC plugin), so the entire ecosystem can benefit from it.
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Similarly, even if a feature provided by a GCC plugin does *not* exist
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in Clang, but the feature is proven to be useful, effort should be spent
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to upstream the feature to GCC (and Clang).
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After a feature is available in upstream GCC, the plugin will be made
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unbuildable for the corresponding GCC version (and later). Once all
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kernel-supported versions of GCC provide the feature, the plugin will
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be removed from the kernel.
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Files
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=====
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**$(src)/scripts/gcc-plugins**
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This is the directory of the GCC plugins.
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**$(src)/scripts/gcc-plugins/gcc-common.h**
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This is a compatibility header for GCC plugins.
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It should be always included instead of individual gcc headers.
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**$(src)/scripts/gcc-plugins/gcc-generate-gimple-pass.h,
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$(src)/scripts/gcc-plugins/gcc-generate-ipa-pass.h,
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$(src)/scripts/gcc-plugins/gcc-generate-simple_ipa-pass.h,
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$(src)/scripts/gcc-plugins/gcc-generate-rtl-pass.h**
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These headers automatically generate the registration structures for
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GIMPLE, SIMPLE_IPA, IPA and RTL passes.
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They should be preferred to creating the structures by hand.
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Usage
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=====
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You must install the gcc plugin headers for your gcc version,
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e.g., on Ubuntu for gcc-10::
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apt-get install gcc-10-plugin-dev
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Or on Fedora::
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dnf install gcc-plugin-devel libmpc-devel
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Or on Fedora when using cross-compilers that include plugins::
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dnf install libmpc-devel
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Enable the GCC plugin infrastructure and some plugin(s) you want to use
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in the kernel config::
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CONFIG_GCC_PLUGINS=y
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CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y
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...
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Run gcc (native or cross-compiler) to ensure plugin headers are detected::
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gcc -print-file-name=plugin
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CROSS_COMPILE=arm-linux-gnu- ${CROSS_COMPILE}gcc -print-file-name=plugin
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The word "plugin" means they are not detected::
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plugin
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A full path means they are detected::
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/usr/lib/gcc/x86_64-redhat-linux/12/plugin
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To compile the minimum tool set including the plugin(s)::
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make scripts
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or just run the kernel make and compile the whole kernel with
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the cyclomatic complexity GCC plugin.
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4. How to add a new GCC plugin
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==============================
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The GCC plugins are in scripts/gcc-plugins/. You need to put plugin source files
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right under scripts/gcc-plugins/. Creating subdirectories is not supported.
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It must be added to scripts/gcc-plugins/Makefile, scripts/Makefile.gcc-plugins
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and a relevant Kconfig file.
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