Susprising behavior of gcc on x86 (-m32)

[Mathieu Malaterre]

On Tue, Sep 8, 2015 at 12:04 PM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> On 8 September 2015 at 10:57, Mathieu Malaterre <malat@debian.org> wrote:
>> On Tue, Sep 8, 2015 at 11:45 AM, Andrew Haley <aph@redhat.com> wrote:
>>> On 09/08/2015 10:15 AM, Mathieu Malaterre wrote:
>>>> What is even more surprising is that I can no longer reproduce the
>>>> behavior using `valgrind` from my 32bits chroot.
>>>>
>>>> I understand that my bug description is relatively small, but I am
>>>> eager to report a more specific gcc issue. If anyone could help me
>>>> narrow down this issue, I'd appreciate your comments.
>>>>
>>>> Please note that that I disabled any kind of optimizations by using
>>>> (explicitly!) -O0.
>>>
>>> I'm guessing that it's some silliness with the FPU, but that's a wild
>>> guess.
>
> That was my first thought too. To rule it out you could compile with
> -mfpmath=sse
>
>
>> Technically this code path is *not* using floating point at all (by
>> JPEG 2000 reversible kernel design). integer based shift&additions
>> operations only.
>
> Then I suggest compiling with -fsanitize=undefined to see if there are
> any undefined shifts.

[...]
/home/mathieu/tmp/opj-bug/openjpeg/src/lib/openjp2/t1.c:1517:28:
runtime error: left shift of negative value -128
[...]

You've saved me hours of time ! Thanks.

for reference:
https://github.com/uclouvain/openjpeg/blob/master/src/lib/openjp2/t1.c#L1517