On Sep 14, 2015 1:15 AM, "Ingo Molnar" <mi...@kernel.org> wrote: > > > * Denys Vlasenko <dvlas...@redhat.com> wrote: > > > >> + /* INT80 syscall entrypoint can be used by > > >> + * 64-bit programs too, unlike SYSCALL/SYSENTER. > > >> + * Therefore it must preserve R12+ > > >> + * (they are callee-saved registers in 64-bit C > > >> ABI). > > >> + * > > >> + * This was probably historically not intended, > > >> + * but R8..11 are clobbered (cleared to 0). > > >> + * IOW: they are the only registers which aren't > > >> + * preserved across INT80 syscall. > > >> + */ > > >> + if (*r64 == 0 && num <= 11) > > >> + continue; > > > > > > Ugh. I'll change my big entry patchset to preserve these and maybe to > > > preserve all of the 64-bit regs. > > > > If you do that, this won't change the ABI: we don't _promise_ > > to save them. If we accidentally do, that means nothing. > > Argh, that's dangerous nonsense! You _still_ don't seem to understand what the > Linux ABI means and how to change code that implements it...
I think Denys might be taking about R8-R11 here. If we change them from clobbered to saved, that's probably fine. Certainly I have to save R12-R15 -- my v1 is just buggy there. I was too deep in __kernel_vsyscall when I wrote that code, and I wasn't thinking about the raw int $0x80 entry variant. I'd be rather surprised if anything broke if we started preserving R8-R11 instead of zeroing them. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
