CFI for saved argument registers

[Andreas Krebbel <krebbel@linux.ibm.com>]

Hi,

I'm trying to provide a simple dwarf unwinder with access to the
argument register content. The goal is to make this information
available for optimized code without having to access debug
information for things like call site args. The extra overhead
of saving the values to the stack is acceptable in that case.

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?

Bye,

Andreas