[PATCH v1 0/2] Introduce the initify gcc plugin

[Emese Revfy]

I would like to introduce the initify gcc plugin. The kernel already has
a mechanism to free up code and data memory that is only used during kernel
or module initialization.
This plugin will teach the compiler to find more such code and data that
can be freed after initialization. It reduces memory usage.
The initify gcc plugin can be useful for embedded systems.

It is a CII project supported by the Linux Foundation.

This plugin is the part of grsecurity/PaX.

The plugin supports all gcc versions from 4.5 to 6.0.

I made some changes on top of the PaX version (since March 6.). These are
the important ones:
 * move all local strings to init.rodata.str and exit.rodata.str
   (not just __func__)
 * report all initified strings and functions
   (GCC_PLUGIN_INITIFY_VERBOSE config option)
 * automatically discover init/exit functions and apply the __init or
   __exit attributes on them

You can find more about the changes here:
https://github.com/ephox-gcc-plugins/initify

This patch set is based on the "Add support for complex gcc plugins that
don't fit in a single file" patch set (git/kees/linux.git#kspp HEAD:
e5d4798b284cd192c8b).

Some statistics about the plugin:

On allyes config (amd64, gcc-6):
* 7731 initified strings
*  231 initified functions

On allmod config (i386, gcc-6):
* 8846 initified strings
*  252 initified functions

On allyes config (amd64, gcc-6):

section         vanilla                 vanilla + initify        change
-----------------------------------------------------------------------
.rodata         39059688 (0x25400e8)    38527210 (0x24be0ea)    -532478
.data           45744128 (0x2ba0000)    45404160 (0x2b4d000)    -339968
.init.data       1361144  (0x14c4f8)     1674200  (0x198bd8)    +313056
.text           77615128 (0x4a05018)    77576664 (0x49fb9d8)     -38464
.init.text       1108455  (0x10e9e7)     1137618  (0x115bd2)     +29163


Emese Revfy (2):
 Add the initify gcc plugin
 Mark functions with the __nocapture attribute

---
 arch/Kconfig                         |   23 +
 arch/arm/include/asm/string.h        |   10 +-
 arch/arm64/include/asm/string.h      |   23 +-
 arch/powerpc/include/asm/string.h    |   19 +-
 arch/x86/boot/string.h               |    4 +-
 arch/x86/include/asm/string_32.h     |   21 +-
 arch/x86/include/asm/string_64.h     |   18 +-
 arch/x86/kernel/hpet.c               |    2 +-
 include/asm-generic/bug.h            |    6 +-
 include/asm-generic/vmlinux.lds.h    |    2 +
 include/linux/compiler-gcc.h         |   10 +-
 include/linux/compiler.h             |    4 +
 include/linux/fs.h                   |    5 +-
 include/linux/printk.h               |    2 +-
 include/linux/string.h               |   73 +--
 scripts/Makefile.gcc-plugins         |    4 +
 scripts/gcc-plugins/initify_plugin.c | 1147 ++++++++++++++++++++++++++++++++++
 17 files changed, 1283 insertions(+), 90 deletions(-)