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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 14 Jul 2022 14:48:37 -0700
Message-ID: <CAHk-=whs05rO37wjdTOgppP-N+mYy70Q2ctBrp6vMoUP=OtcVA@mail.gmail.com>
Subject: Re: [PATCH] ubsan: disable UBSAN_DIV_ZERO for clang
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Tom Rix <trix@redhat.com>, Marco Elver <elver@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        clang-built-linux <llvm@lists.linux.dev>,
        Alexander Potapenko <glider@google.com>
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On Thu, Jul 14, 2022 at 2:38 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> int do_div (int dividend, int divisor) {
>   return dividend / divisor;
> }
>
> has UB should divisor ever be zero, not much different from:

So?

What about the million other '/' in the kernel?

Adding one check to 'do_div()' is just stupid. It's like using a
bottle-cap as an umbrella.

Nick, that's the whole _point_ of having compiler support for things
like this - automation. Because doing them manually one at a time is
just completely broken and stupid.

                Linus