Re: [PATCH] MIPS: Mark check_bugs{,_early}() as __init

From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <nathan@kernel.org>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: jpoimboe@kernel.org, peterz@infradead.org,
	linux-mips@vger.kernel.org,  linux-kernel@vger.kernel.org,
	llvm@lists.linux.dev, patches@lists.linux.dev
Subject: Re: [PATCH] MIPS: Mark check_bugs{,_early}() as __init
Date: Wed, 19 Apr 2023 15:03:31 -0700	[thread overview]
Message-ID: <CAKwvOdmuQBnZR_pB5bUdsF+OoB_4pxBT9TNFF83fZhzwZ1gbxw@mail.gmail.com> (raw)
In-Reply-To: <20230419-mips-check_bugs-init-attribute-v1-1-91e6eed55b89@kernel.org>

On Wed, Apr 19, 2023 at 11:43 AM Nathan Chancellor <nathan@kernel.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@kernel.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?

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

>
> -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@kernel.org>
>

-- 
Thanks,
~Nick Desaulniers