CFI for saved argument registers

[Florian Weimer]

* Andreas Krebbel via Gcc:

> For that purpose I save the argument registers to the stack as we
> would do for a variable argument lists. But this time I also provide
> the CFI to allow the unwinder to locate the save slots.  Since I never
> actually intend to restore the content there is no matching
> cfi_restore for the cfi_offset and dwarf2cfi complains about the
> traces being inconsistent because of that. I couldn't find a way to
> prevent this.
>
> The only way I see right now is adding a new reg note to invalidate
> the save information in the reg_save array in dwarf2cfi.
>
> Would this be acceptable? Is there perhaps an easier way to achieve that?

This is very interesting.  I think we should do this in glibc for abort
and __assert_fail for as many registers as possible, hopefully
preserving more information for debuggers.

Thanks,
Florian