Consider the following scenario: SIGPIPE has SA_ONSTACK handler, SIGSEGV - non-SA_ONSTACK one. SIGPIPE is delivered and we fail halfway through setting a sigframe for it. OK, we get SIGSEGV forced in, which gets handled not on altstack. But what should happen if we fail *after* having saved the altstack settings into the sigframe that got abandoned? AFAICS, we get them reset and the original setting entirely lost. Shouldn't that thing be applied only after we have succeeded in building the frame? In signal_delivered(), perhaps... I realize that this is out of scope for POSIX, so it's not a matter of standard compliance, but it looks like a bit of a QoI issue...
