[lkml]   [2019]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 4/7] module: avoid code duplication in include/linux/export.h
On 29/10/2019 20.19, Jessica Yu wrote:
> +++ Rasmus Villemoes [27/09/19 13:07 +0200]:
>> On 27/09/2019 11.36, Masahiro Yamada wrote:
>>> A typical kernel configuration has 10K exported symbols, so it
>>> increases 10KB in rough estimation.
>>> I did not come up with a good idea to refactor it without increasing
>>> the code size.
>> Can't we put the "aMS" flags on the __ksymtab_strings section? That
>> would make the empty strings free, and would also deduplicate the
>> USB_STORAGE string. And while almost per definition we don't have exact
>> duplicates among the names of exported symbols, we might have both a foo
>> and __foo, so that could save even more.
>> I don't know if we have it already, but we'd need each arch to tell us
>> what symbol to use for @ in @progbits (e.g. % for arm). It seems most
>> are fine with @, so maybe a generic version could be
>> #endif
>> and then it would be
>> section("__ksymtab_strings,\"aMS\","ARCH_SECTION_TYPE_CHAR"progbits,1")
> FWIW, I've just tinkered with this, and unfortunately the strings
> don't get deduplicated for kernel modules :-(
> Apparently ld does not do the deduplication for SHF_MERGE|SHF_STRINGS
> sections for relocatable files (ld -r), which kernel modules are. See:

I know <> :)

> But, the strings do get deduplicated for vmlinux. Not sure if we can
> find a workaround for modules or if the benefit is significant enough
> if it only for vmlinux.

I think it's definitely worth if, even if it "only" benefits vmlinux for
now. And I still hope to revisit the --force-section-merge some day, but
it's very far down my priority list.


 \ /
  Last update: 2019-10-29 22:12    [W:0.161 / U:3.232 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site