Introduction¶

GCC plugins are loadable modules that provide extra features to thecompiler[1]. They are useful for runtime instrumentation and static analysis.We can analyse, change and add further code during compilation viacallbacks[2], GIMPLE[3], IPA[4] and RTL passes[5].

The GCC plugin infrastructure of the kernel supports all gcc versions from4.5 to 6.0, building out-of-tree modules, cross-compilation and building in aseparate directory.Plugin source files have to be compilable by both a C and a C++ compiler as wellbecause 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 andpowerpc architectures.

This infrastructure was ported from grsecurity[6] and PaX[7].

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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 ingcc-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 forGIMPLE, SIMPLE_IPA, IPA and RTL passes. They support all gcc versionsfrom 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

Or on Fedora:

dnf install gcc-plugin-devel

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 withthe 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 directoryhere. 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.