Saving to 32 bits of GPRs in signal context

[Ulrich Weigand]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 05/29/2007 
09:24:15 AM:

> Specifically, are everybody using the uc_regs pointer to get to the
> mcontext or are some people likely to expect the mcontext to always be
> at the same offset from the beginning of the signal frame ?

As far as I can see, both GDB and the GCC unwind-from-signal code
always read the uc_regs pointer. (Or the sigcontext.regs pointer for
old-style signal frames.)

> There are a few other issues... one is, the pad fields aren't cleared.
> Thus how can userland or rt_sigreturn differenciate between a valid
> highregs pointers and ramdom junk ? Is there a trick one of you can come
> up with that I could do to let userland/gdb/rt_sigreturn know that
> there's something there ?

One idea we had about this was to use a bit in uc_flags.  Those are
completely unused today, but should always have been initialized to 0.


Mit freundlichen Gruessen / Best Regards

Ulrich Weigand

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