Messages in this thread | | | Date | Sat, 5 Jul 2003 09:39:46 +0200 | From | Jörn Engel <> | Subject | Re: [PATCH 2.5.73] Signal stack fixes #1 introduce PF_SS_ACTIVE |
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On Sat, 5 July 2003 09:18:21 +1000, Paul Mackerras wrote: > > This is madness. > > There is nothing in POSIX that says that you have to exit a signal > handler by returning from it (which, under Linux, ends up doing a > sigreturn or rt_sigreturn system call). It is explicitly permitted to > return from a RT signal handler with setcontext(), for instance. And > it is at least long-standing practice to return using longjmp(). > Neither setcontext nor longjmp will do a system call (yes, setcontext > is a system call on sparc, but it isn't on x86 AFAIK). > > So - the kernel doesn't (and can't and shouldn't need to) know about > all transitions to or from a signal stack. Therefore the PF_SS_ACTIVE > bit is useless since it will be wrong some of the time.
Ack.
> Anyway, what is the problem with taking a signal on the signal stack > when you in a signal handler using the signal stack? You just keep > going down the stack from where you are, which is what the code > already does.
The problem is with a broken signal handler, that moves the stack pointer to nirvana. You get a signal, set up the signal stack, move the pointer to nirvana, get a signal, set up the signal stack, move the pointer to nirvana, get a signal, ...
If I was just going down the signal stack, I would be perfectly happy, but instead the kernel believes each signal is the very first on the signal stack and sets it up again (and again...) each time.
> BTW, I am the PPC maintainer; Ben is the powermac maintainer.
Sorry about that.
Jörn
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