On Mon, 2007-01-22 at 09:57 +0100, Xavier Roche wrote: > Hi folks, > > I have a probably louzy question regarding sigaction() behaviour when an > alternate signal stack is used: it seems that I can not get the user > stack reference in the ucontext_t stack context ; ie. the uc_stack > member contains reference of the alternate signal stack, not the stack > that was used before the crash. > > Is this is a normal behaviour ? Is there a way to retrieve the original > user's stack inside the signal callback ? > > The example given below demonstrates the issue: > top of stack==0x7fffff3d7000, alternative_stack==0x501010 > SEGV==0x7fffff3d6ff8; sp==0x501010; current stack is the alternate stack > > It is obvious that the SEGV was a stack overflow: the si_addr address is > just on the page below the stack limit.
POSIX says: "the third argument can be cast to a pointer to an object of type ucontext_t to refer to the receiving thread's context that was interrupted when the signal was delivered." so if uc_stack doesn't point to the stack in use immediately prior to signal generation, this is a bug. (In theory I should be able to pass the ucontext_t supplied to the signal handler to setcontext() and resume execution exactly where I left off -- glibc's refusal to support kernel-generated ucontexts gets in the way of this, but the point still stands.) I have no idea who to bother about i386 signal delivery, though. (And I suspect this bug has probably been copied to other architectures as well.) -- Nicholas Miell <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/