[Qemu-devel] [sparc64] Miscomputed minimum of a group of numbers in sparc64 emulation

[Jakub Jermar]

Hi,

we have been observing a problem with HelenOS running on the latest git
Qemu/sparc64. The gist of the problem is that the following computation
of minimum of 64 and 512 surprisingly gives 512:

 bytes = min(len, BPS(bs) - pos % BPS(bs));
 bytes = min(bytes, nodep->size - pos);

On input, `len` is 64, `pos` is 0, `BPS(bs)` is 512 and `nodep->size` is
some bigger number. Surprisingly, in a non-single-stepping mode, Qemu
computes `bytes` as 512 instead of 64. When singlestepping via GDB, the
result is correct.

I think this could be a bug in Qemu so I am attaching the relevant
portion of qemu.log with some comments and pointers in it.

I would appreciate if someone who understands the sparc64 code
translation could have a look at this. More debugging data may be
provided upon request.

Thanks,
Jakub

qemu.log
Description: Text Data