linux-kernel - Re: [PATCH v3 1/2] x86/purgatory: do not use __builtin_memcpy and __builtin

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Message-ID: <alpine.DEB.2.21.1907241231480.1972@nanos.tec.linutronix.de>
Date:   Wed, 24 Jul 2019 12:33:03 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
cc:     mingo@...hat.com, bp@...en8.de, peterz@...radead.org,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        yamada.masahiro@...ionext.com, stable@...r.kernel.org,
        Vaibhav Rustagi <vaibhavrustagi@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Alistair Delva <adelva@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Enrico Weigelt <info@...ux.net>,
        Allison Randal <allison@...utok.net>,
        Uros Bizjak <ubizjak@...il.com>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>
Subject: Re: [PATCH v3 1/2] x86/purgatory: do not use __builtin_memcpy and
 __builtin_memset

On Tue, 23 Jul 2019, Nick Desaulniers wrote:
> Instead, reuse an implementation from arch/x86/boot/compressed/string.c
> if we define warn as a symbol. Also, Clang may lower memcmp's that
> compare against 0 to bcmp's, so add a small definition, too. See also:
> commit 5f074f3e192f ("lib/string.c: implement a basic bcmp")
> 
> Cc: stable@...r.kernel.org
> Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality")
> Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056
> Reported-by: Vaibhav Rustagi <vaibhavrustagi@...gle.com>
> Debugged-by: Vaibhav Rustagi <vaibhavrustagi@...gle.com>
> Debugged-by: Manoj Gupta <manojgupta@...gle.com>
> Suggested-by: Alistair Delva <adelva@...gle.com>
> Signed-off-by: Vaibhav Rustagi <vaibhavrustagi@...gle.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

That SOB chain is weird. Is Vaibhav the author?

> +/*
> + * Clang may lower `memcmp == 0` to `bcmp == 0`.
> + */
> +int bcmp(const void *s1, const void *s2, size_t len) {
> +	return memcmp(s1, s2, len);
> +}

foo()
{
}

please.

Thanks,

	tglx