linux-kernel - Re: [PATCH 0/2] Use dot prefixes for section names

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Message-ID: <Zw5a-JH99HwxhoY3@pathway.suse.cz>
Date: Tue, 15 Oct 2024 14:08:33 +0200
From: Petr Mladek <pmladek@...e.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
	Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	linux-mm@...ck.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 0/2] Use dot prefixes for section names

On Mon 2024-10-14 20:19:32, Ard Biesheuvel wrote:
> On Mon, 14 Oct 2024 at 20:10, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > On Mon, 14 Oct 2024 at 10:44, Ard Biesheuvel <ardb@...nel.org> wrote:
> > >
> > > We have this code in arch/x86/Makefile.postlink:
> > >
> > > quiet_cmd_strip_relocs = RSTRIP  $@
> > >       cmd_strip_relocs = \
> > >         $(OBJCOPY) --remove-section='.rel.*' --remove-section='.rel__*' \
> > >                    --remove-section='.rela.*' --remove-section='.rela__*' $@
> > >
> > > Of course, that could easily be fixed, I was just being cautious in
> > > case there is other, out-of-tree tooling for live patch or kexec etc
> > > that has similar assumptions wrt section names.
> >
> > I'd actually much rather just make strip_relocs not have that "." and
> > "__" pattern at all, and just say "we strip all sections that start
> > with '.rel'".
> >
> > And then we make the rule that we do *not* create sections named ".rel*".
> >
> > That seems like a much simpler rule, and would seem to simplify
> > strip_relocs too, which would just become
> >
> >         $(OBJCOPY) --remove-section='.rel*' $@
> >
> > (We seem to have three different copies of that complex pattern with
> > .rel vs .rela and "." vs "__" - it's in s390, riscv, and x86. So we'd
> > do that simplification in three places)
> >
> > IOW, I'd much rather make our section rules simpler rather than more complex.
> >
> > Of course, if there is some active and acute problem report with this
> > thing, we might not have that option, but in the absence of any
> > *known* issue with just simplifying things, I'd rather do that.
> >
> 
> I don't disagree with any of this. CC'ing folks working on live patch
> in case they have any insights.

The livepatching specific sections use the name pattern:

	.klp.rela.objname.section_name

They are generated by a post processing of the livepatch module.
The code is not upstream at the moment. It is implemented by
some out-of-tree tools which are used to build the livepatches.

More details can be found in
Documentation/livepatch/module-elf-format.rst

Best Regards,
Petr