[PATCH v2 0/3] Introduce the initify gcc plugin

Emese Revfy
2016-07-04T23:33:08Z

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
(https://github.com/ephox-gcc-plugins/gcc-plugins_linux-next.git#initify
HEAD: e08eda5d85f7f52641640).

Some statistics about the plugin:

On allyes config (amd64, gcc-6):
* 7765 initified strings
* 231 initified functions

On allmod config (i386, gcc-6):
* 9177 initified strings
* 288 initified functions

On allyes config (amd64, gcc-6):

section vanilla vanilla + initify change
-----------------------------------------------------------------------
.rodata 19054824 (0x122c0e8) 18841832 (0x11f80e8) -212992
.init.data 1273768 (0x136fa8) 1583496 (0x182988) +309728
.text 46126301 (0x2bfd4dd) 46099805 (0x2bf6d5d) -26496
.init.text 836339 (0x0cc2f3) 855952 (0x0d0f90) +19613
.exit.data 104 (0x000068) 16736 (0x004160) +16632
.exit.text 125511 (0x01ea47) 133267 (0x020893) +7756

FileSiz (vanilla) FileSiz (vanilla + initify) change
------------------------------------------------------------------------
00 67727360 (0x4097000) 65417216 (0x3e63000) -2310144
03 2453504 (0x257000) 2809856 (0x2ae000) +356352

00 .text .notes __ex_table .rodata __bug_table .pci_fixup .builtin_fw
.tracedata __ksymtab __ksymtab_gpl __ksymtab_strings __init_rodata
__param __modver
03 .init.text .altinstr_aux .init.data .x86_cpu_dev.init
.parainstructions .altinstructions .altinstr_replacement
.iommu_table .apicdrivers .exit.text .exit.data .smp_locks .bss .brk

On defconfig (amd64, gcc-6):
* 2044 initified strings
* 43 initified functions

On defconfig (amd64, gcc-6):

section vanilla vanilla + initify change
-----------------------------------------------------------------------
.rodata 2466736 (0x25a3b0) 2405296 (0x24b3b0) -61440
.init.data 564656 (0x089db0) 645616 (0x09d9f0) +80960
.text 9364727 (0x8ee4f7) 9360823 (0x8ed5b7) -3904
.init.text 436097 (0x06a781) 439161 (0x06b379) +3064
.exit.data 0 864 (0x000360) +864
.exit.text 8806 (0x002266) 9824 (0x002660) +1018

FileSiz (vanilla) FileSiz (vanilla + initify) change
------------------------------------------------------------------------
00 13340672 (0xcb9000) 13279232 (0xcaa000) -61440
03 1097728 (0x10c000) 1183744 (0x121000) +86016

00 .text .notes __ex_table .rodata __bug_table .pci_fixup .builtin_fw
.tracedata __ksymtab __ksymtab_gpl __ksymtab_strings __init_rodata
__param __modver
03 .init.text .altinstr_aux .init.data .x86_cpu_dev.init
.parainstructions .altinstructions .altinstr_replacement
.iommu_table .apicdrivers .exit.text .exit.data .smp_locks .bss .brk

Emese Revfy (3):
Add the initify gcc plugin
Mark functions with the __nocapture attribute
Constify some function parameters

Changes from v1:
* Removed unnecessary nocapture attributes from boot code
(Reported-by: PaX Team <pageexec@freemail.hu>)
* Removed nocapture attributes from functions that return
the marked parameter
(Reported-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>)
* Added nocapture attribute to strlen()
* Updated gcc-common.h from PaX
* Don't forcibly constify initified string types
this caused the size reduction of the .data section
(initify_plugin.c)
* Added the section mismatch problem in the commit message

---
arch/Kconfig | 23 +
arch/arm/include/asm/string.h | 4 +-
arch/arm64/include/asm/string.h | 19 +-
arch/powerpc/include/asm/string.h | 19 +-
arch/x86/include/asm/string_32.h | 21 +-
arch/x86/include/asm/string_64.h | 20 +-
arch/x86/kernel/hpet.c | 2 +-
drivers/isdn/hisax/config.c | 4 +-
drivers/isdn/hisax/hisax.h | 4 +-
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 | 63 +-
scripts/Makefile.gcc-plugins | 4 +
scripts/gcc-plugins/gcc-common.h | 41 ++
scripts/gcc-plugins/initify_plugin.c | 1183 ++++++++++++++++++++++++++++++++++
19 files changed, 1353 insertions(+), 83 deletions(-)