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GCC plugin infrastructure

1. 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].


2. Files

	This is the directory of the GCC plugins.

	This is a compatibility header for GCC plugins.
	It should be always included instead of individual gcc headers.

	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++).

	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.

3. 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:


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.