Date: Sun, 9 Aug 2020 09:54:31 +0200 From: Markus Wichmann <nullplan@....net> To: musl@...ts.openwall.com Subject: Re: Revisiting sigaltstack and implementation-internal signals On Sat, Aug 08, 2020 at 08:39:58PM -0400, Rich Felker wrote: > on it (possibly not even any signal handlers installed), and (2) > whether we should care about breaking code that swaps off of and back > onto the alternate signal stack with swapcontext. Would anything bad happen in that case? I thought, when a signal handler with SA_ONSTACK is invoked, the altstack is marked with SS_ONSTACK and will not be reset until the signal handler returns. If the handler does not return, and does not call sigaltstack(), then the SS_ONSTACK remains set, and therefore further signals with SA_ONSTACK will be delivered on the current stack. Otherwise, if a signal were to arrive while the altstack is in use, it would overwrite the old stack. I cannot find a source code for swapcontext, but to my knowledge it merely combines setjmp() and longjmp(), right? (setjmp() for the current context and longjmp() for the other one). So no call to sigaltstack(). Ciao, Markus
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