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

Mathias Krause
2016-06-28T17:09:29Z

Hi Emese,

On Tue, Jun 28, 2016 at 01:34:07PM +0200, Emese Revfy wrote:
> 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

You should probably provide numbers for .init.rodata.str, .exit.rodata.str
and .exit.text as well. Otherwise this delta calculation suggests a rather
gigantic image size reduction which is probably not the case ;)

Also a comparison of the final kernel image size would be nice to see if
the string duplication issue mentioned in [1] is actually an issue.

[1] http://marc.info/?l=linux-kernel&m=140364632417795&w=2

Thanks,
Mathias

>
>
> 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(-)