On Tue, Jul 16, 2013 at 1:24 AM, Jakub Jelinek <ja...@redhat.com> wrote: > On Mon, Jul 15, 2013 at 10:40:04PM -0500, Peter Bergner wrote: >> On Mon, 2013-07-15 at 23:03 -0400, David Edelsohn wrote: >> > On Mon, Jul 15, 2013 at 4:26 PM, Peter Bergner <berg...@vnet.ibm.com> >> > wrote: >> > > David, do you prefer reverting the above hunk from the Power HTM >> > > patch or should I add the associated -mno-* options to the building >> > > of libitm? >> > >> > How is libitm built for Intel? The principle of least surprises >> > suggests following that precedent. >> >> They use -mrtm (like we use -mhtm) to build libitm, but it looks like >> their -mrtm does not enable any other isa flags like we currently are >> doing with -mhtm. Meaning their -mrtm option is independent of any >> -mcpu values while ours is not. If we revert the patch I mentioned, >> then I think we will match what Intel is doing. >> Hopefully Jakub will correct me if I am wrong. > > Yes, that is my understanding of it too. On Intel we have: > #define OPTION_MASK_ISA_RTM_SET OPTION_MASK_ISA_RTM > #define OPTION_MASK_ISA_RTM_UNSET OPTION_MASK_ISA_RTM > which means that -mrtm doesn't set any other options except for itself > and -mno-rtm doesn't reset other options. libitm is built with -mrtm, > assuming that the only thing the -mrtm switch affects are the HTM builtins > and that those will only be found explicitly in code guarded with the > htm_available () runtime check. > Right now, -mhtm on PowerPC basically implies -march=power8 if I understand > the code well, and libitm is built with it, which means essentially that > when gcc is configured for a pre-power8 CPU, libitm will work just fine on > power8 (including HTM support), but when running on power7 and earlier > it might very well SIGILL, because the implicit -march=power8 could affect > even code not guarded by htm_available (). > And on s/390, right now we enable HTM support in libitm when configured for > -march=zEC12 by default (which isn't ideal).
Then I agree that the hunk should be reverted so that HTM does not imply POWER8. Thanks, David
