On 11 February 2013 11:28, James Hogan <james.hogan@xxxxxxxxxx> wrote: > On 11/02/13 10:13, Vineet Gupta wrote: >> On Monday 11 February 2013 03:06 PM, Jonas Bonn wrote: >>> On 11 February 2013 08:26, Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx> wrote: >>> >>>> The only downside of this patch is that userspace signal stack grows in size, >>>> since signal frame only cares about scratch regs (pt_regs), but has to accommodate >>>> unused placeholder for callee regs too by virtue of using user_regs_struct. >>> Is this really true? Don't setcontext and friends require that _all_ >>> the registers be part of sigcontext? >> >> But for an ABI - callee saved regs will anyhow be saved/restored even in >> setcontext case ! So collecting it for that purpose seems useless, or am I missing >> something here. > > I think Jonas' point was that signals are asynchronous, i.e. you could > get interrupted by a signal at virtually any time during the program's > execution. No, I agree that the callee-saved regs don't need to be saved across a signal handler invocation. It's really just the setcontext case that wants to be able to swap out the callee-saved regs. And now that I think about it some more, I think this is done incorrectly in the openrisc arch, too, as the fast-path for rt_sigreturn probably only restores the call-clobbered regs. sigreturn probably needs to be special-cased to _always_ restore all the regs on its way back to userspace. Not for the "signal" case, but for the "setcontext" case; but these two are pretty-much indistinguishable. /Jonas -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
