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Re: RFA: DW_AT_frame_base fix for complicated frames
- From: Jim Blandy <jimb at redhat dot com>
- To: Daniel Jacobowitz <drow at mvista dot com>
- Cc: gdb-patches at sources dot redhat dot com, dberlin at dberlin dot org
- Date: 02 Oct 2003 12:54:32 -0500
- Subject: Re: RFA: DW_AT_frame_base fix for complicated frames
- References: <20031002165606.GA22819@nevyn.them.org>
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.