Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 133 insertions, 0 deletions

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+=========================
+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.