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

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Message-ID: <CAMVonLgwzj2vjKtgXJG2=U04-w+29TZhgykeNYRbWTT55wtNMg@mail.gmail.com>
Date:   Wed, 24 Jul 2019 13:55:47 -0700
From:   Vaibhav Rustagi <vaibhavrustagi@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        yamada.masahiro@...ionext.com, stable@...r.kernel.org,
        Manoj Gupta <manojgupta@...gle.com>,
        Alistair Delva <adelva@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <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 Wed, Jul 24, 2019 at 3:33 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> 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?
>
No, Nick Desaulniers is the author of v3.

> > +/*
> > + * 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
Thanks,
Vaibhav