Documentation/gcc-plugins.txt      |  76 +++++++++++++++++++++++++++
 2 files changed, 179 insertions(+)
 create mode 100644 Documentation/example_gcc_plugin.c
 create mode 100644 Documentation/gcc-plugins.txt

diff --git a/Documentation/example_gcc_plugin.c b/Documentation/example_gcc_plugin.c
new file mode 100644
index 0000000..950ff78
--- /dev/null
+++ b/Documentation/example_gcc_plugin.c

@@ -0,0 +1,103 @@
+/*
+ * Copyright 2011-2016 by Emese Revfy <re.emese@gmail.com>
+ * Licensed under the GPL v2, or (at your option) v3
+ */
+
+#include "gcc-common.h"
+
+int plugin_is_GPL_compatible;
+
+static struct plugin_info example_plugin_info = {
+       .version        = "0",
+       .help           = "example plugin\n",
+};
+
+static unsigned int handle_function(void)
+{
+       gimple_stmt_iterator gsi;
+       basic_block bb;
+
+       FOR_ALL_BB_FN(bb, cfun) {
+               for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi))
+                       debug_gimple_stmt(gsi_stmt(gsi));
+       }
+       return 0;
+}
+
+#if BUILDING_GCC_VERSION >= 4009
+namespace {
+static const struct pass_data example_plugin_pass_data = {
+#else
+static struct gimple_opt_pass example_plugin_pass = {
+       .pass = {
+#endif
+               .type                   = GIMPLE_PASS,
+               .name                   = "example_plugin",
+#if BUILDING_GCC_VERSION >= 4008
+               .optinfo_flags          = OPTGROUP_NONE,
+#endif
+#if BUILDING_GCC_VERSION >= 5000
+#elif BUILDING_GCC_VERSION >= 4009
+               .has_gate               = false,
+               .has_execute            = true,
+#else
+               .gate                   = NULL,
+               .execute                = handle_function,
+               .sub                    = NULL,
+               .next                   = NULL,
+               .static_pass_number     = 0,
+#endif
+               .tv_id                  = TV_NONE,
+               .properties_required    = 0,
+               .properties_provided    = 0,
+               .properties_destroyed   = 0,
+               .todo_flags_start       = 0,
+               .todo_flags_finish      = TODO_dump_func
+#if BUILDING_GCC_VERSION < 4009
+       }
+#endif
+};
+
+#if BUILDING_GCC_VERSION >= 4009
+class example_plugin_pass : public gimple_opt_pass {
+public:
+       example_plugin_pass() : gimple_opt_pass(example_plugin_pass_data, g) {}
+#if BUILDING_GCC_VERSION >= 5000
+       virtual unsigned int execute(function *) { return handle_function(); }
+#else
+       unsigned int execute() { return handle_function(); }
+#endif
+};
+}
+
+static opt_pass *make_example_plugin_pass(void)
+{
+       return new example_plugin_pass();
+}
+#else
+static struct opt_pass *make_example_plugin_pass(void)
+{
+       return &example_plugin_pass.pass;
+}
+#endif
+
+int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version)
+{
+       const char * const plugin_name = plugin_info->base_name;
+       struct register_pass_info example_plugin_pass_info;
+
+       example_plugin_pass_info.pass                           = make_example_plugin_pass();
+       example_plugin_pass_info.reference_pass_name            = "ssa";
+       example_plugin_pass_info.ref_pass_instance_number       = 1;
+       example_plugin_pass_info.pos_op                         = PASS_POS_INSERT_AFTER;
+
+       if (!plugin_default_version_check(version, &gcc_version)) {
+               error(G_("incompatible gcc/plugin versions"));
+               return 1;
+       }
+
+       register_callback(plugin_name, PLUGIN_INFO, NULL, &example_plugin_info);
+       register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &example_plugin_pass_info);
+
+       return 0;
+}

diff --git a/Documentation/gcc-plugins.txt b/Documentation/gcc-plugins.txt
new file mode 100644
index 0000000..e669d83
--- /dev/null
+++ b/Documentation/gcc-plugins.txt

@@ -0,0 +1,76 @@
+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.
+
+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++).
+
+
+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, $(src)/Makefile and
+$(src)/arch/Kconfig.
+See the cyc_complexity_plugin.c (CONFIG_GCC_PLUGIN_CYC_COMPLEXITY) GCC plugin.
+
+
+5. Example GCC plugin
+=====================
+
+You can find an example plugin under $(src)/Documentation/example_gcc_plugin.c .
+This plugin has a GIMPLE pass that is inserted after the ssa GCC pass.
+It prints out all the GIMPLE statements in a translation unit.