Re: frame->unwind->this_base()

Andrew Cagney
2003-03-17T00:09:10Z

> On Sun, Mar 16, 2003 at 05:04:36PM -0500, Andrew Cagney wrote:
>
>> At present there is a per-frame ID method since different frames
>> determine their ID using different techniques. The ID (which identifies
>> a given frame instance) includes a base and pc/func value.
>>
>> GDB's frame code also makes available the get_frame_base() method.
>> While the default implementation returns get_frame_id().base, I think
>> there is going to need to be a per-frame frame->unwind->this_base method.
>>
>> For dwarf2 frames, it would return, DW_AT_frame_base. For prologue
>> frames, it would return an attempt at an equivalent value. Hopefully it
>> wouldn't be called for other frame types :-).
>>
>> It might even be reasonable for a prologue based unwinder to error out
>> when asked for the frame's base before the stack frame has been created.
>>
>> Thoughts?
>>
>> I should note that dwarf2expr.c contains code that tries to
>> locally/directly evaluate the frame base. I think that should instead
>> do a get_frame_base() call.
>
>
> There's no guarantee right now that the DW_AT_frame_base agrees with
> the frame's base. I don't even think it's necessary that they be the
> same.

There is certainly no guarentee that the DW_AT_frame_base and `struct
frame_id.base' match.

However, shouldn't the only thing needing the `virtual frame pointer' /
get_frame_base() be the code that needs a virtual base pointer when
computing the value of a local variable?

Andrew