linux-kernel - Re: [PATCH] MIPS: Mark check_bugs{,_early}() as _

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Message-ID: <20230419233710.GA1314058@dev-arch.thelio-3990X>
Date:   Wed, 19 Apr 2023 16:37:10 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        jpoimboe@...nel.org, peterz@...radead.org,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev
Subject: Re: [PATCH] MIPS: Mark check_bugs{,_early}() as __init

On Wed, Apr 19, 2023 at 03:03:31PM -0700, Nick Desaulniers wrote:
> On Wed, Apr 19, 2023 at 11:43 AM Nathan Chancellor <nathan@...nel.org> wrote:
> >
> > After commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING
> > forcibly"), a compiler may choose not to inline a function marked with
> > just 'inline'. If check_bugs() is not inlined into start_kernel(), which
> > occurs when building with clang after commit 9ea7e6b62c2b ("init: Mark
> > [arch_call_]rest_init() __noreturn"), modpost complains with:
> >
> >   WARNING: modpost: vmlinux.o: section mismatch in reference: check_bugs (section: .text) -> check_bugs32 (section: .init.text)
> >
> > check_bugs() is only called from start_kernel(), which itself is marked
> > __init, so mark check_bugs() as __init as well to clear up the warning
> > and make everything work properly.
> >
> > While there is currently no warning about check_bugs_early(), it could
> > have the same problem, as it is called from arch_setup() and calls
> > check_bugs64_early(), both marked __init. Mark it as __init for the same
> > reason as above.
> >
> > Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> > ---
> > NOTE: This is based on v6.3-rc7, as the issue shows up due to a patch in
> > the tip tree, but this appears to be an ancient issue that could have
> > showed up at any point (hence why no explicit Fixes tag), so I chose a
> > base that should allow either the MIPS or tip folks to apply this patch.
> 
> Probably for the MIPS tree.
> 
> >
> > Additionally, I was tempted to remove the explicit 'inline' since the
> > compiler is free to do whatever it wants anyways but this is a static
> > function in a header so we would need to add '__maybe_unused', which is
> > already added with 'inline' in a normal build so I just left it alone.
> > ---
> >  arch/mips/include/asm/bugs.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/mips/include/asm/bugs.h b/arch/mips/include/asm/bugs.h
> > index d72dc6e1cf3c..9b9bf9bc7d24 100644
> > --- a/arch/mips/include/asm/bugs.h
> > +++ b/arch/mips/include/asm/bugs.h
> > @@ -24,13 +24,13 @@ extern void check_bugs64_early(void);
> >  extern void check_bugs32(void);
> >  extern void check_bugs64(void);
> >
> > -static inline void check_bugs_early(void)
> > +static inline void __init check_bugs_early(void)
> >  {
> >         if (IS_ENABLED(CONFIG_CPU_R4X00_BUGS64))
> >                 check_bugs64_early();
> >  }
> 
> If the only call site is in arch/mips/kernel/setup.c, then perhaps we
> can move the definition of check_bugs_early there and mark it static
> __init and drop inline?

Sure, we could even go a step further and just copy the body into the
one call site ourselves, I see little reason for this to be a dedicated
function. That is probably best done in a separate patch altogether in
lieu of just adding __init.

> Unless we foresee other callers potentially in the future?  Patch
> otherwise LGTM.  Thanks for the patch!

Seems unlikely, I did a super scientific survey of several different
revisions (:P) and check_bugs_early() is called once in each one:

v3.0:arch/mips/kernel/setup.c:    check_bugs_early();
v3.5:arch/mips/kernel/setup.c:    check_bugs_early();
v3.10:arch/mips/kernel/setup.c:    check_bugs_early();
v4.0:arch/mips/kernel/setup.c:    check_bugs_early();
v4.5:arch/mips/kernel/setup.c:    check_bugs_early();
v5.0:arch/mips/kernel/setup.c:    check_bugs_early();
v4.10:arch/mips/kernel/setup.c:    check_bugs_early();
v5.5:arch/mips/kernel/setup.c:    check_bugs_early();
v5.10:arch/mips/kernel/setup.c:    check_bugs_early();
v6.0:arch/mips/kernel/setup.c:    check_bugs_early();

I'll do whatever Thomas would prefer.

> >
> > -static inline void check_bugs(void)
> > +static inline void __init check_bugs(void)
> >  {
> >         unsigned int cpu = smp_processor_id();
> >
> >
> > ---
> > base-commit: 6a8f57ae2eb07ab39a6f0ccad60c760743051026
> > change-id: 20230419-mips-check_bugs-init-attribute-026103bdb255
> >
> > Best regards,
> > --
> > Nathan Chancellor <nathan@...nel.org>
> >
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers