linux-kernel - Re: [PATCH] include/uapi/linux/swab: Fix potentially missing __always

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Date:   Wed, 28 Sep 2022 15:36:02 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Matt Redfearn <matt.redfearn@...s.com>,
        Petr Vaněk <arkamar@...as.cz>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, Justin Stitt <jstitt007@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        "open list:CLANG/LLVM BUILD SUPPORT" <llvm@...ts.linux.dev>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-perf-users@...r.kernel.org>, mmayer@...adcom.com,
        Khem Raj <raj.khem@...il.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] include/uapi/linux/swab: Fix potentially missing
 __always_inline

Hi Florian,

On Tue, Sep 27, 2022 at 02:52:56PM -0700, Florian Fainelli wrote:
> From: Matt Redfearn <matt.redfearn@...s.com>
> 
> Commit bc27fb68aaad ("include/uapi/linux/byteorder, swab: force inlining
> of some byteswap operations") added __always_inline to swab functions
> and commit 283d75737837 ("uapi/linux/stddef.h: Provide __always_inline to
> userspace headers") added a definition of __always_inline for use in
> exported headers when the kernel's compiler.h is not available.
> 
> However, since swab.h does not include stddef.h, if the header soup does
> not indirectly include it, the definition of __always_inline is missing,
> resulting in a compilation failure, which was observed compiling the
> perf tool using exported headers containing this commit:
> 
> In file included from /usr/include/linux/byteorder/little_endian.h:12:0,
>                  from /usr/include/asm/byteorder.h:14,
>                  from tools/include/uapi/linux/perf_event.h:20,
>                  from perf.h:8,
>                  from builtin-bench.c:18:
> /usr/include/linux/swab.h:160:8: error: unknown type name `__always_inline'
>  static __always_inline __u16 __swab16p(const __u16 *p)
> 
> Fix this by replacing the inclusion of linux/compiler.h with
> linux/stddef.h to ensure that we pick up that definition if required,
> without relying on it's indirect inclusion. compiler.h is then included
> indirectly, via stddef.h.
> 
> Fixes: 283d75737837 ("uapi/linux/stddef.h: Provide __always_inline to userspace headers")
> Signed-off-by: Matt Redfearn <matt.redfearn@...s.com>
> Reviewed-by: Petr Vaněk <arkamar@...as.cz>
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>

I took this through my kernel build matrix and did not see any new
issues.

Tested-by: Nathan Chancellor <nathan@...nel.org>

Cheers,
Nathan

> ---
> Apologies for the insanely long CC list. I encountered this problem
> again while attempting to build perf with a LLVM 13 toolchain using
> musl-libc. Not sure why it did not get picked up last time?
> 
> Khem did submit an alternative patch a few years ago, too which also did
> not get picked up:
> 
> https://lore.kernel.org/lkml/20180913005654.39976-1-raj.khem@gmail.com/
> 
>  include/uapi/linux/swab.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h
> index 0723a9cce747..01717181339e 100644
> --- a/include/uapi/linux/swab.h
> +++ b/include/uapi/linux/swab.h
> @@ -3,7 +3,7 @@
>  #define _UAPI_LINUX_SWAB_H
>  
>  #include <linux/types.h>
> -#include <linux/compiler.h>
> +#include <linux/stddef.h>
>  #include <asm/bitsperlong.h>
>  #include <asm/swab.h>
>  
> -- 
> 2.25.1
> 
>