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From:   Vaibhav Rustagi <vaibhavrustagi@google.com>
Date:   Wed, 24 Jul 2019 13:55:47 -0700
Message-ID: <CAMVonLgwzj2vjKtgXJG2=U04-w+29TZhgykeNYRbWTT55wtNMg@mail.gmail.com>
Subject: Re: [PATCH v3 1/2] x86/purgatory: do not use __builtin_memcpy and __builtin_memset
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        yamada.masahiro@socionext.com, stable@vger.kernel.org,
        Manoj Gupta <manojgupta@google.com>,
        Alistair Delva <adelva@google.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Enrico Weigelt <info@metux.net>,
        Allison Randal <allison@lohutok.net>,
        Uros Bizjak <ubizjak@gmail.com>,
        Chao Fan <fanc.fnst@cn.fujitsu.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Alexios Zavras <alexios.zavras@intel.com>
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On Wed, Jul 24, 2019 at 3:33 AM Thomas Gleixner <tglx@linutronix.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@vger.kernel.org
> > Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality")
> > Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056
> > Reported-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
> > Debugged-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
> > Debugged-by: Manoj Gupta <manojgupta@google.com>
> > Suggested-by: Alistair Delva <adelva@google.com>
> > Signed-off-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.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