linux-kernel - Re: [PATCH v2] kasan: don't emit builtin calls when sanitization is off

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Message-ID: <CAAeHK+z=7UBwVyyDLi8jLbMg5PHdqr-RaqiUFgkdLcMFfie4Vg@mail.gmail.com>
Date:   Mon, 22 Jan 2018 18:22:37 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Stephen Hines <srhines@...gle.com>,
        Pirama Arumuga Nainar <pirama@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Majnemer <majnemer@...gle.com>,
        Chandler Carruth <chandlerc@...gle.com>,
        Michael Kuperstein <mkuper@...gle.com>
Subject: Re: [PATCH v2] kasan: don't emit builtin calls when sanitization is off

On Fri, Jan 19, 2018 at 8:06 PM, Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
> Hmm... I had mentioned this patch to some coworkers who have much more
> knowledge about LLVM than me.  They had concern that LLVM needs memset
> to be defined, and that there were discussions on the llvm mailing
> list about this.
>
> I'm digging through trying to find anything relevant, maybe this one
> about memcpy: https://lists.llvm.org/pipermail/llvm-dev/2012-May/050108.html
>
> I wonder if -ffreestanding is more appropriate?

I don't mind using either of those, they both fix the issue.

I'm struggling to understand the difference though. GCC documentation
doesn't really explain it [1] and Clang documentation [2] is
completely useless in this case.

[1] https://gcc.gnu.org/onlinedocs/gcc/Standards.html
[2] https://clang.llvm.org/docs/CommandGuide/clang.html