Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix

[Paolo Bonzini]

On 02/11/2015 15:09, Peter Maydell wrote:
>> > diff --git a/target-sparc/vis_helper.c b/target-sparc/vis_helper.c
>> > index 383cc8b..45fc7db 100644
>> > --- a/target-sparc/vis_helper.c
>> > +++ b/target-sparc/vis_helper.c
>> > @@ -447,7 +447,7 @@ uint32_t helper_fpackfix(uint64_t gsr, uint64_t rs2)
>> >      for (word = 0; word < 2; word++) {
>> >          uint32_t val;
>> >          int32_t src = rs2 >> (word * 32);
>> > -        int64_t scaled = src << scale;
>> > +        int64_t scaled = (int64_t)src << scale;
>> >          int64_t from_fixed = scaled >> 16;
> This will now shift left into the sign bit of a signed integer,
> which is undefined behaviour.

Why "now"?  It would have done the same before.

Paolo