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From: Arnd Bergmann <arnd@arndb.de>
Date: Fri, 3 Mar 2017 09:58:54 +0100
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Subject: Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Denys Vlasenko <dvlasenk@redhat.com>
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On Fri, Mar 3, 2017 at 12:05 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> I assume '-Wdiv-by-zero' is enabled and gcc isn't showing the "division
> by zero" warning for either of these?  The 'ud2' is guaranteed to
> trigger since the function has no branches.  Surely at least the missing
> warning is a gcc bug.
>
> The good news is objtool is flushing these out, albeit with a confusing
> message.

I'm still not sure if it's intentional or not. I've reduced the test case to the
simple

static inline int return0(void) { return 0; }
int provoke_div0_warning(void) { return 1 / return0(); }

which does not generate a compile-time warning, but will generate
an unconditional runtime warning if built with -fsanitze=integer-divide-by-zero.

     Arnd