On Thu, Jun 18, 2015 at 3:11 AM, Ingo Molnar <mi...@kernel.org> wrote: > > * Andy Lutomirski <l...@amacapital.net> wrote: > >> > The only low level bits remaining in assembly will be low level hardware >> > ABI >> > details: saving registers and restoring registers to the expected format - >> > no >> > 'active' code whatsoever. >> >> I think this is true for syscalls. Getting the weird special cases (IRET >> and GS >> fault) for error_entry to work correctly in C could be tricky. > > Correct, and I double checked the IRET fault path yesterday (fixup_bad_iret), > and > it looks like a straightforward exception handler with limited control flow. > It > can stay in asm just fine, it seems mostly orthogonal to the rest. > > I didn't check the GS fault path, but that only affects 32-bit, as we use > SWAPGS > on 64-bit, right? In any case, that code too (32-bit RESTORE_REGS) belongs > into > the natural 'hardware ABI preparation code' that should stay in assembly. > (Unless > I missed some other code that might cause trouble.)
Look for "gs_change". To change the gs selector, we do swapgs, then load gs, then swapgs again. If the gs load fails, then we trigger a special fixup. --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/
