linux-kernel - Re: [tip: objtool/core] objtool: Use sh_info to find the base for .rela sections

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Date:   Tue, 16 Jun 2020 17:11:28 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86 <x86@...nel.org>,
        linux-tip-commits@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [tip: objtool/core] objtool: Use sh_info to find the base for
 .rela sections

On Tue, Jun 16, 2020 at 09:27:49PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 16, 2020 at 11:00:59AM -0700, Kees Cook wrote:
> > On Wed, Apr 22, 2020 at 10:24:44PM -0000, tip-bot2 for Sami Tolvanen wrote:
> > > The following commit has been merged into the objtool/core branch of tip:
> > > 
> > > Commit-ID:     e2ccbff8f02d6b140b8ee71108264686c19b1c78
> > > Gitweb:        https://git.kernel.org/tip/e2ccbff8f02d6b140b8ee71108264686c19b1c78
> > > Author:        Sami Tolvanen <samitolvanen@...gle.com>
> > > AuthorDate:    Tue, 21 Apr 2020 11:25:01 -07:00
> > > Committer:     Josh Poimboeuf <jpoimboe@...hat.com>
> > > CommitterDate: Tue, 21 Apr 2020 18:49:15 -05:00
> > > 
> > > objtool: Use sh_info to find the base for .rela sections
> > > 
> > > ELF doesn't require .rela section names to match the base section. Use
> > > the section index in sh_info to find the section instead of looking it
> > > up by name.
> > > 
> > > LLD, for example, generates a .rela section that doesn't match the base
> > > section name when we merge sections in a linker script for a binary
> > > compiled with -ffunction-sections.
> > > 
> > > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> > > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > > Reviewed-by: Kees Cook <keescook@...omium.org>
> > 
> > Hi!
> > 
> > Where did this commit end up? It seems to have vanished (404 on the
> > Gitweb link) and isn't in -next nor Linus's tree.
> > 
> > This is needed for LTO, FGKASLR, and link speed improvements[1]. Is it
> > possible to get this landed in -rc2 so all the things depending on it
> > can rebase happily?
> 
> I can't remember why this happened, however I think this patch is in
> josh's objtool tree that I was going to stick in objtool/core
> tomorrow-ish.

Okay, thanks!

> Are those things you mentioned still slated for this release?

No, the three things I mentioned aren't for v5.8 (they're still under
development), but sending their respective series without the -tip
patches in -rc2 will result in redundant patches. (So, it's hardly the
end of the world, but it's just a confusing state to be in since they
appeared in -tip and then never ended up in the merge window. It'd be
helpful to have them in place for things that will base their latest
tree on v5.8-rc2.)

-- 
Kees Cook