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From: Marco Elver <elver@google.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-kbuild@vger.kernel.org,
	Masahiro Yamada <masahiroy@kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	Arnd Bergmann <arnd@arndb.de>,
	stable@vger.kernel.org, Ard Biesheuvel <ardb@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Rikard Falkeborn <rikard.falkeborn@gmail.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kbuild: avoid static_assert for genksyms
Date: Thu, 10 Dec 2020 17:12:20 +0100	[thread overview]
Message-ID: <X9JI5KpWoo23wkRg@elver.google.com> (raw)
In-Reply-To: <20201203230955.1482058-1-arnd@kernel.org>

On Fri, Dec 04, 2020 at 12:09AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> genksyms does not know or care about the _Static_assert() built-in,
> and sometimes falls back to ignoring the later symbols, which causes
> undefined behavior such as
> 
> WARNING: modpost: EXPORT symbol "ethtool_set_ethtool_phy_ops" [vmlinux] version generation failed, symbol will not be versioned.
> ld: net/ethtool/common.o: relocation R_AARCH64_ABS32 against `__crc_ethtool_set_ethtool_phy_ops' can not be used when making a shared object
> net/ethtool/common.o:(_ftrace_annotated_branch+0x0): dangerous relocation: unsupported relocation
> 
> Redefine static_assert for genksyms to avoid that.
> 
> Cc: stable@vger.kernel.org
> Suggested-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  include/linux/build_bug.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
> index e3a0be2c90ad..7bb66e15b481 100644
> --- a/include/linux/build_bug.h
> +++ b/include/linux/build_bug.h
> @@ -77,4 +77,9 @@
>  #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
>  #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
>  
> +#ifdef __GENKSYMS__
> +/* genksyms gets confused by _Static_assert */
> +#define _Static_assert(expr, ...)
> +#endif
> +

I had sent

	https://lkml.kernel.org/r/20201201152017.3576951-1-elver@google.com

3 days before your patch. :-)

I guess what you propose is simpler, but might still have corner cases
where we still get warnings. In particular, if some file (for whatever
reason) does not include build_bug.h and uses a raw _Static_assert(),
then we still get warnings. E.g. I see 1 user of raw _Static_assert()
(drivers/gpu/drm/amd/amdgpu/amdgv_sriovmsg.h ).

In the end I don't mind either way, as long as those warnings are fixed
in 5.11. :-)

Thanks,
-- Marco

      parent reply	other threads:[~2020-12-10 16:15 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-03 23:09 [PATCH] kbuild: avoid static_assert for genksyms Arnd Bergmann
2020-12-06  2:48 ` Masahiro Yamada
2020-12-07  8:53   ` Ard Biesheuvel
2020-12-10 16:12 ` Marco Elver [this message]

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