On Wed, Sep 22, 2010 at 12:08:53PM -0700, Linus Torvalds wrote: > On Wed, Sep 22, 2010 at 11:53 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > Um, no. ?You've *already* called get_signal_to_deliver(). ?There had been > > no SIGSEGV in sight. ?You happily went on to set a sigframe for e.g. > > SIGHUP, but ran out of stack. ?At that point you get force_sigsegv() > > from handle_signal(). ?_NOW_ you have a pending SIGSEGV > > Ahh. Ok. Different case from the one I thought you were worried about. > And yeah, I guess that one does require us to mess with the low-level > asm code (although I do wonder if we could not make the whole > do_notify_resume + reschedule code be generic C code - it's a lot of > duplicated subtle asm as it is). Worse than just that... Note that on sparc you need to deal with fault_in_user_windows(), which can also trigger signals. So much for merging it cross-architecture, even if we ignore the differences between the ways we pass data required for restart to do_signal(). Note that e.g. on alpha we pass _two_ values - one for overwritten v0 (syscall number), another for overwritten a3 (error flag), etc. Worse, quite a few targets do not save all registers on syscall entry. Callee-saved stuff doesn't have to be in pt_regs. Except that you want *all* of them saved on stack when it's time to fill sigframes. And once you've entered a C function you can't guarantee that compiler hasn't already modified them; sure, they'll be restored on return, but that doesn't help you to get to their values. So you get switch_stack built on stack around calling do_notify_resume() on those. And you really want to avoid doing that if you've got no signals - remember, we hit that on exit from irqs as well, so it's one hell of a hot path. For processors with big flat register file it can get very ugly. There is a lot of ugly almost-duplication in there, no arguments about that. Asm glue is actually not the worst part... -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
