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Re: [Qemu-devel] [PULL 2/9] QEMU does not care about left shifts of sign


From: Peter Maydell
Subject: Re: [Qemu-devel] [PULL 2/9] QEMU does not care about left shifts of signed negative values
Date: Wed, 25 Nov 2015 17:44:10 +0000

On 25 November 2015 at 17:19, Paolo Bonzini <address@hidden> wrote:
> Ubsan also has warnings for undefined behavior of left shifts.  Checks for
> left shift overflow and left shift of negative numbers, unfortunately,
> cannot be silenced without also silencing the useful ones about out-of-range
> shift amounts. -fwrapv ought to shut them up, but doesn't yet
> (https://llvm.org/bugs/show_bug.cgi?id=25552; I am taking care of fixing
> the same issues in GCC).  Luckily ubsan is optional, and the easy
> workaround is to use -fsanitize-recover.

We still haven't had any response from the LLVM/clang folks that
this interpretation of the meaning of -fwrapv is their interpretation
of it, have we? (I can't see any comments on the referenced bug.)

thanks
-- PMM



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