On Thu, Nov 27, 2014 at 11:41:40AM -0600, Peter Bergner wrote: > On Thu, 2014-11-27 at 10:08 -0600, Segher Boessenkool wrote: > > On Wed, Nov 26, 2014 at 05:50:27PM -0600, Peter Bergner wrote: > > > Nope, you don't get a SIGILL when executing 64-bit instructions in > > > 32-bit mode, so it'll happily just execute the instruction, doing > > > a full 64-bit compare. I'm guessing that the upper 32-bits of both > > > r3 and r4 contain zeros, so we're probably just getting lucky. > > > > You will get a SIGILL if you run on 32-bit hardware. > > Ha, I completely forgot about 32-bit hardware. Anyway, I looked > at the ISA, and cmpdi and cmpwi are just extended mnemonics for > cmpi, with cmpdi setting the L field to 1. Probably on 32-bit > hardware, the hardware is just ignoring the L bit being set and > doing a cmpwi for us???
Huh. Yes, maybe some implementations do that. The good news is that those then compute the correct thing ;-) Can QEMU help catch such bugs more reliably? Segher _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev