Re: rt_sigreturn rejects a substitute stack frame as invalid.

[Mikael Pettersson]

Steven Stewart-Gallus writes:
 > Hello,
 > 
 > I'm not totally sure that GLibc's setcontext is safe to use in a
 > signal handler. So, I decided I was going to play things safe and let
 > rt_sigreturn switch stacks for me instead. However, rt_sigreturn seems
 > to reject my substitute stack frame as invalid and I'm not sure why.

I did similar things at my previous work (doing dynamic binary
instrumentation and virtualization of user-space binaries; can't
share the code alas, it's proprietary), but my code operated
directly on top of the kernel/user-space API, using the actual
kernel/user-space data structures rather than glibc's fake ones.

If you're sure that it's the kernel's rt_sigreturn and not whatever
glibc runs before it that complains, then a simple way of debugging
this is to modify your kernel to printk some diagnostics whenever
rt_sigreturn decides to error out.

You may also want to check out the 'pth' package.
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