lkml.org 
[lkml]   [2021]   [Jan]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v3] x86/entry: emit a symbol for register restoring thunk
On Mon, Jan 11, 2021 at 5:00 PM Borislav Petkov <bp@alien8.de> wrote:
>
> On Mon, Jan 11, 2021 at 04:41:52PM -0800, Fāng-ruì Sòng wrote:
> > To be fair: we cannot use
>
> Who's "we"?
>
> > .L-prefixed local because of the objtool limitation.
>
> What objtool limitation? I thought clang's assembler removes .text which
> objtool uses. It worked fine with GNU as so far.

I don't think we need to completely stop using .L prefixes in the
kernel, just this one location since tracking the control flow seems a
little tricky for objtool. Maybe Josh can clarify more if needed?

>
> > The LLVM integrated assembler behavior is a good one
>
> Please explain what "good one" means in that particular context.
>
> > and binutils global maintainers have agreed so H.J. went ahead and
> > implemented it for GNU as x86.
>
> But they don't break old behavior, do they? Or are they removing .text
> unconditionally now too?

Unconditionally. See
https://sourceware.org/pipermail/binutils/2021-January/114700.html
where that flag was rejected and the optimization was adopted as the
optimization was obvious to GNU binutils developers. So I suspect this
will become a problem for GNU binutils users as well after the latest
release that contains
https://sourceware.org/pipermail/binutils/attachments/20210105/75dd4a9d/attachment-0001.bin.

> > --generate-unused-section-symbols=[yes|no] as an assembler option has
> > been rejected.
>
> Meaning what exactly? There's no way for clang's integrated assembler to
> even get a cmdline option to not strip .text?

I can clean that up in v5; The section symbols were not generated then
stripped; they were simply never generated.
--
Thanks,
~Nick Desaulniers

\
 
 \ /
  Last update: 2021-01-12 02:15    [W:1.478 / U:0.092 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site