linux-kernel - Re: [PATCH 3/3] include/uapi/linux/swab: Fix potentially missing __always

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Message-ID: <YQFgbRXKIeZ7H6mo@arkam>
Date:   Wed, 28 Jul 2021 15:49:33 +0200
From:   Petr Vaněk <arkamar@...as.cz>
To:     Pavo Banicevic <pavo.banicevic@...tura.hr>
Cc:     linux@...linux.org.uk, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, nathan@...nel.org,
        ndesaulniers@...gle.com, ivan.khoronzhuk@...aro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        clang-built-linux@...glegroups.com, matt.redfearn@...s.com,
        mingo@...nel.org, dvlasenk@...hat.com, juraj.vijtiuk@...tura.hr,
        robert.marko@...tura.hr, luka.perkov@...tura.hr,
        jakov.petrina@...tura.hr
Subject: Re: [PATCH 3/3] include/uapi/linux/swab: Fix potentially missing
 __always_inline

On Tue, Jul 27, 2021 at 04:11:19PM +0200, Pavo Banicevic 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>
> ---

I use this patch in order to fix __always_inline issue for kernels
5.12+, see https://lore.kernel.org/lkml/YPGXXt6Z3O1W0AYS@arkam/ .
I believe this is the correct solution.

Reviewed-by: Petr Vaněk <arkamar@...as.cz>