=========================

  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 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 [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/
  
  
  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.

  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.