Re: FYI: fix big-endian bug with DWARF_VALUE_STACK

[Tom Tromey <tromey@redhat.com>]

>>>>> "Ulrich" == Ulrich Weigand <uweigand@de.ibm.com> writes:

Tom> +	    store_unsigned_integer (contents + offset, n,
Tom> +				    gdbarch_byte_order (c->arch),
Tom> +				    p->v.expr.value);

Ulrich> The original code looks broken to me too.  But even the new code
Ulrich> doesn't seem quite right: if the requested piece size p->size
Ulrich> is larger than addr_size, the remaining bytes of the output value
Ulrich> are left undefined (well, probably zeroed -- but that still doesn't
Ulrich> look correct on a big-endian machine ...).

I asked about a similar case on dwarf-discuss, namely what if you have:

  DW_OP_implicit_value[len=5] DW_OP_piece[len=10]

The answer I got was something along the lines of "that is undefined,
don't do that".

The archives seem to be closed to the public, but if you are a
subscriber you can see:

    http://lists.dwarfstd.org/htdig.cgi/dwarf-discuss-dwarfstd.org/2009-June/000760.html

I think the same has to apply to your example.

Ulrich> Why would that code look at gdbarch_addr_bit at all?  I think this
Ulrich> should simply do something like:

Ulrich> 	    store_unsigned_integer (contents + offset, p->size,
Ulrich> 				    gdbarch_byte_order (c->arch),

Yeah ... I took another look and I still don't understand that use in
read_pieced_value.  Maybe a complaint is in order here.

Tom> @@ -476,19 +474,17 @@ dwarf2_evaluate_loc_desc (struct symbol *var, struct frame_info *frame,

Ulrich> Similiary here; why does this not simply use value_from_longest?

It didn't occur to me; but AFAIK, nothing prohibits a DWARF expression
from using DW_OP_stack_value to fill in a structure or union, and
value_from_longest won't work in that case.

Tom