linux-kernel - Re: [PATCH v1 1/1] compiler_types: Warn about unused static inline functions on second

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Message-ID: <20251106151649.GA1693433@ax162>
Date: Thu, 6 Nov 2025 08:16:49 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v1 1/1] compiler_types: Warn about unused static inline
 functions on second

On Thu, Nov 06, 2025 at 11:50:00AM +0100, Andy Shevchenko wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> Per Nathan, clang catches unused "static inline" functions in C files since
> commit 6863f5643dd7 ("kbuild: allow Clang to find unused static inline
> functions for W=1 build").
> 
> Linus said:
> 
> > So I entirely ignore W=1 issues, because I think so many of the extra
> > warnings are bogus.
> >
> > But if this one in particular is causing more problems than most -
> > some teams do seem to use W=1 as part of their test builds - it's fine
> > to send me a patch that just moves bad warnings to W=2.
> >
> > And if anybody uses W=2 for their test builds, that's THEIR problem..
> 
> Here is the change to bump the warning from W=1 to W=2.
> 
> Fixes: 6863f5643dd7 ("kbuild: allow Clang to find unused static inline functions for W=1 build")
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

I can take this as a fix via kbuild or Linus can apply it directly
but...

> ---
>  include/linux/compiler_types.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 59288a2c1ad2..575a03643fa1 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -253,7 +253,7 @@ struct ftrace_likely_data {
>   * for W=1 build. This will allow clang to find unused functions. Remove the
>   * __inline_maybe_unused entirely after fixing most of -Wunused-function warnings.
>   */

The comment should be updated to W=2 instead of W=1 and we should
probably drop the sentence about removing __inline_maybe_unused entirely
since people such as Peter will never want this behavior by default. I
do not mind doing it myself if I take it.

> -#ifdef KBUILD_EXTRA_WARN1
> +#ifdef KBUILD_EXTRA_WARN2
>  #define __inline_maybe_unused
>  #else
>  #define __inline_maybe_unused __maybe_unused
> -- 
> 2.50.1
>