linux-kernel - Re: linux-next: build warning after merge of the powerpc tree

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Message-ID: <20230217070544.uhe337i5xsgwsum4@treble>
Date:   Thu, 16 Feb 2023 23:05:44 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build warning after merge of the powerpc tree

On Fri, Feb 17, 2023 at 12:35:17PM +1100, Michael Ellerman wrote:
> Josh Poimboeuf <jpoimboe@...nel.org> writes:
> > On Thu, Feb 16, 2023 at 02:40:31PM +1100, Stephen Rothwell wrote:
> >> Hi all,
> >> 
> >> After merging the powerpc tree, today's linux-next build (powerpc
> >> pseries_le_defconfig) produced this warning:
> >> 
> >> arch/powerpc/kernel/head_64.o: warning: objtool: .text+0x6128: unannotated intra-function call
> >> 
> >> I have no idea what caused this.
> >
> > Adding Sathvika and Christophe.
> >
> > The short term fix would be something like the below, but...
> >
> > If powerpc objtool is only doing mcount, does it even make sense to run
> > objtool on asm files?  If so, there are probably a lot more cleanups
> > needed for the asm code.
> 
> I would like to enable more of the objtool checks eventually, although I
> don't have a timeline for that. But I'd prefer to keep checking the asm
> code seeing as we've already enabled that.

Sounds good for now, though as you get more objtool features there will
need to be more changes.

For example a lot of the callable functions are annotated with _GLOBAL()
rather than SYM_FUNC_{START,END}.  The latter adds the function size,
which objtool needs in several cases.  It also has particular rules
about when to use SYM_FUNC_* vs SYM_CODE_*, etc to make the code more
structured.

> > So I'm thinking either we should cleanup all the powerpc asm code with
> > annotations like below, or we should try to make objtool mcount-mode
> > ignore asm files.
> 
> I think we have most of the code annotated already, this is a new
> warning because that code is newly refactored by a commit I applied.
> 
> I'll have to fix my build scripts to error out on objtool warnings.

Likewise, I'll need to add some powerpc cross-compiles to my testing.

If we get too many of these powerpc warnings, we may be looking to
recruit more objtool maintainers ;-)

-- 
Josh