lkml.org 
[lkml]   [2021]   [Oct]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 00/16] x86: Rewrite the retpoline rewrite logic
On Tue, Oct 26, 2021 at 02:01:32PM +0200, Peter Zijlstra wrote:
> Hi,
>
> These patches rewrite the way retpolines are rewritten. Currently objtool emits
> alternative entries for most retpoline calls. However trying to extend that led
> to trouble (ELF files are horrid).
>
> Therefore completely overhaul this and have objtool emit a .retpoline_sites
> section that lists all compiler generated retpoline thunk calls. Then the
> kernel can do with them as it pleases.
>
> Notably it will:
>
> - rewrite them to indirect instructions for !RETPOLINE
> - rewrite them to lfence; indirect; for RETPOLINE_AMD,
> where size allows (boo clang!)
>
> Specifically, the !RETPOLINE case can now also deal with the clang-special
> conditional-indirect-tail-call:
>
> Jcc __x86_indirect_thunk_\reg.
>
> Finally, also update the x86 BPF jit to catch up to recent times and do these
> same things.
>
> All this should help improve performance by removing an indirection.
>
> Patches can (soon) be found here:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git objtool/core
>
> Changes since v2:
>
> - rewrite the __x86_indirect_thunk_array[] stuff again
> - rewrite the retpoline,amd rewrite logic, it now also supports
> rewriting the Jcc case, if the original instruction is long enough, but
> more importantly, it's simpler code.
> - bpf label simplification patch
> - random assorted cleanups
> - actually managed to get bpf selftests working

Good stuff!

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

--
Josh

\
 
 \ /
  Last update: 2021-10-28 07:17    [W:0.189 / U:0.544 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site