Re: [RFA][1/5] New port: Cell BE SPU (dwarf2loc.c fix)

Jim Blandy
2006-11-13T19:40:16Z

"Ulrich Weigand" <uweigand@de.ibm.com> writes:
> this fixes a problem in dwarf2loc.c that triggers for the SPU port.
>
> The code in dwarf_expr_read_reg currently expects that in order to
> retrieve an address value from a register, it's OK to assume the
> address can always be extracted using extract_unsigned_integer
> on the full size of the register.
>
> This fails on the SPU, because all registers are 16 bytes wide, and
> a pointer is represented by simply using the uppermost 4 bytes and
> ignoring the contents of the remaining 12 bytes. I would assume
> that there's also other architectures where the assumption in
> dwarf_expr_read_reg might fail, e.g. due to sign extension issues
> or other required fiddling.
>
> So, to fix this I thought that we already *know* how to extract
> values of a certain type from a register: value_from_register does
> just that, and provides all sorts of configurability for the back
> end to have it just do the right thing. Since the value retrieved
> by dwarf_expr_read_reg is always a pointer to some data object
> (normally on the stack), it should be OK to get it by using
> value_from_register (builtin_type_void_data_ptr, ...).
>
> This is what the patch below does, and it works fine on SPU.
> Additionally tested without regressions on s390-ibm-linux and
> s390x-ibm-linux.

This seems fine. I tested it on i686 Fedora Core 5 and didn't see any
new failures.

Would it be a good idea to introduce a new function, a companion to
value_from_register, that wraps up the composition of
value_from_register and value_as_address?