Re: [Qemu-devel] [PULL 00/40] ppc patch queue 2015-06-03

[Peter Maydell]

On 5 June 2015 at 16:20, Paolo Bonzini <address@hidden> wrote:
> On 05/06/2015 17:08, Peter Maydell wrote:
>>> > Can someone add a checkpatch rule that forbids shifting left U or UL
>>> > constants (i.e. only ULL)?  That would alleviate my concerns with these
>>> > ubsan warnings.
>>
>> ...but things like "(1U << 31)" are entirely valid.
>
> They're only valid until someone does a ~ on them.  I think it's
> reasonable to forbid them in our coding standards, if we want to fix
> ubsan's warning of (1 << 31).
>
> I don't think it's reasonable for compiler writers to exploit the
> undefinedness of (1 << 31) anyway, and if it were possible to shut up
> ubsan about this particular kind of undefined behavior, I would prefer it.

I just checked, and it isn't possible to suppress this particular
shift warning without also turning off others that we would want
to retain.

The ppc code is still provoking this sanitizer warning in my
test runs :-(

thanks
-- PMM