Re: [Qemu-devel] [PULL 0/9] Misc patches for QEMU 2.5-rc2 (2015-11-25)

[Peter Maydell]

On 26 November 2015 at 10:40, Paolo Bonzini <address@hidden> wrote:
>
>
> On 26/11/2015 10:46, Peter Maydell wrote:
>> I definitely don't think we should apply the -fwrapv patch yet;
>> would you mind respinning this pullrequest without it?
>
> In what way does that patch make that thing worse?

It makes a claim about the semantics that the compiler
guarantees us which isn't currently valid. (Or
alternatively, it's implicitly claiming that clang isn't
a supported compiler, which isn't true.) I don't think
we should document or rely on signed-shift semantics
until we have the relevant documented promises from the
compiler developers that that is what they are providing.
(I'm happy that the gcc folks have provided those promises, they
just need to actually document them in the -fwrapv option
docs. The clang folks haven't replied yet so we don't know.)

thanks
-- PMM