RFA: DW_AT_frame_base fix for complicated frames

[Daniel Jacobowitz <drow@mvista.com>]

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.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

2003-10-02  Daniel Jacobowitz  <drow@mvista.com>

	* dwarf2expr.c (execute_stack_op): Don't treat the frame base as
	a memory pointer.

Index: dwarf2expr.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2expr.c,v
retrieving revision 1.9
diff -u -p -r1.9 dwarf2expr.c
--- dwarf2expr.c	22 Jul 2003 15:41:59 -0000	1.9
+++ dwarf2expr.c	2 Oct 2003 16:43:21 -0000
@@ -441,18 +441,6 @@ execute_stack_op (struct dwarf_expr_cont
 	    result = dwarf_expr_fetch (ctx, 0);
 	    if (ctx->in_reg)
 	      result = (ctx->read_reg) (ctx->baton, result);
-	    else
-	      {
-		char *buf = alloca (TARGET_ADDR_BIT / TARGET_CHAR_BIT);
-		int bytes_read;
-
-		(ctx->read_mem) (ctx->baton, buf, result,
-				 TARGET_ADDR_BIT / TARGET_CHAR_BIT);
-		result = dwarf2_read_address (buf,
-					      buf + (TARGET_ADDR_BIT
-						     / TARGET_CHAR_BIT),
-					      &bytes_read);
-	      }
 	    result = result + offset;
 	    ctx->stack_len = before_stack_len;
 	    ctx->in_reg = 0;