Re: RFA: DW_AT_frame_base fix for complicated frames

[Jim Blandy <jimb at redhat dot com>]

Daniel Jacobowitz <drow@mvista.com> writes:
> Does anyone remember a specific reason why this code was there?  I don't,
> and I rewrote all of this stuff... I am 99.99% sure it's based on the unwind
> handling for saved registers, where we get either a register number or the
> address of a stack slot.  But for frame bases that's not true:
> 
> A subroutine or entry point entry may also have a DW_AT_frame_base
> attribute, whose value is a location description that computes the "frame
> base" for the subroutine or entry point.
> 
> i.e. it computes the frame base.  Not the address of the frame base.  This
> memory read tends to find (on x86) the return address, and then we think the
> stack is at <main+34>.  Oopsie.
> 
> OK?  With this patch and some code Daniel Berlin and Joseph are working on,
> location lists actually work.  I can see all the arguments in an
> -fomit-frame-pointer function from the beginning.  It's really quite cool.

I think you're right, there's no reason for that memory fetch to be
there.  Please commit.