Jeremy Fitzhardinge wrote: > On 09/03/09 22:06, Tejun Heo wrote: >>>> Heh... here's a naive and hopeful plan. How about we beg gcc >>>> developers to allow different segment register and offset in newer gcc >>>> versions and then use the same one when building with the new gcc? >>>> This should solve the i386 problem too. It would be the best as we >>>> get to keep the separate segment register from the userland. Too >>>> hopeful? >>>> >>> I think it's possible to set the register in more recent gcc. Doing the >>> sane thing and having a symbol for an offset is probably worse. >>> >> I was thinking about altering the build process so that we can use sed >> to substitute %gs:40 with %fs:40 while compiling. If it's already >> possible to override the register in more recent gcc, no need to go >> into that horror. >> > > Ideally we'd like to get rid of the constant offset too. If we could > change it to %[fg]s:__gcc_stack_canary_offset on both 32-bit and 64-bit, > it would give us a lot more flexibility. __gcc_stack_canary_offset > could be weakly defined to 20/40 for backwards compatibility, but we > could override it to point to a normal percpu variable. Yeap, being able to do that will also allow using single segment register on i386 too. But given that the only overhead we're talking here is a few more cycles when entering and leving the kernel, I don't think we need to do anything drastic to optimize this. I think converting when gcc provides the feature should be enough. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html