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/

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

Enable the GCC plugin infrastructure and some plugin(s) you want to use in the kernel config:

CONFIG_GCC_PLUGINS=y
CONFIG_GCC_PLUGIN_CYC_COMPLEXITY=y
CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y
...

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. See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin.