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Date: Wed, 17 Feb 2016 16:35:15 -0800
From: Kees Cook <keescook@...omium.org>
To: Emese Revfy <re.emese@...il.com>
Cc: linux-kbuild <linux-kbuild@...r.kernel.org>, PaX Team <pageexec@...email.hu>,
Brad Spengler <spender@...ecurity.net>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Michal Marek <mmarek@...e.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v2 3/3] Documentation for the GCC plugin infrastructure
On Thu, Feb 11, 2016 at 2:43 PM, Emese Revfy <re.emese@...il.com> wrote:
> This is the GCC infrastructure documentation about its operation, how to add
> and use a new plugin with an example.
> ---
> Documentation/gcc-plugins.txt | 68 +++++++++++++++++++++++++++++++++++++++++++
> arch/Kconfig | 2 ++
> 2 files changed, 70 insertions(+)
> create mode 100644 Documentation/gcc-plugins.txt
>
> diff --git a/Documentation/gcc-plugins.txt b/Documentation/gcc-plugins.txt
> new file mode 100644
> index 0000000..e1171c2
> --- /dev/null
> +++ b/Documentation/gcc-plugins.txt
> @@ -0,0 +1,68 @@
> +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.
> +
> +Currently the GCC plugin infrastructure supports only the x86 architecture.
What's needed to support other 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/
> +
> +
> +2. Files
> +========
> +
> +$(src)/tools/gcc
> + This is the directory of the GCC plugins.
> +
> +$(src)/tools/gcc/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++).
The part about the proper host compiler isn't clear to me. It looks
like each of three compilers are examined:
$CC for the header location
$HOSTCC for actually doing the build, or
$HOSTCXX for doing the plugin build?
Shouldn't the headers be coming from the compiler that is actually
going to be used to build the .so file?
> +
> +
> +3. Usage
> +========
> +
> +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)/tools/gcc/. You can use a file or a directory
> +here. It must be added to $(src)/tools/gcc/Makefile,
> +$(src)/scripts/Makefile.gcc-plugins and $(src)/arch/Kconfig.
> +See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin.
> diff --git a/arch/Kconfig b/arch/Kconfig
> index a558ecb..38964dd 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -377,6 +377,8 @@ config GCC_PLUGIN_CYC_COMPLEXITY
> N = the number of nodes
> P = the number of connected components (exit nodes).
>
> + See Documentation/gcc-plugins.txt for details.
> +
> endmenu # "GCC plugins"
>
> config HAVE_CC_STACKPROTECTOR
> --
> 2.4.1
Thanks! I'm looking forward to more plugins. :)
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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