http://sourceware.org/ml/gdb-patches/2009-06/msg00191.html

GCC developers would like to change GCC to emit DW_OP_call_frame_cfa,

as this would reduce the size of the generated debuginfo.

A prerequisite to this is that GDB understand this.  So, this patch

implements this feature.  This is PR 10224.

I'm interested in feedback on this.  I am not sure whether the

implementation of dwarf2_frame_cfa is ok.

No test case since at some point GCC will start generating this

(perhaps optionally -- but I feel certain we'll do it by default in

Fedora), and since it therefore seemed like a lot of work for little

payoff.

Tom

2009-06-08  Tom Tromey  <tromey@redhat.com>

	PR gdb/10224:

	* dwarf2loc.c: Include dwarf2-frame.h.

	(dwarf_expr_frame_cfa): New function.

	(dwarf2_evaluate_loc_desc): Initialize new field.

	(needs_frame_frame_cfa): New function.

	(dwarf2_loc_desc_needs_frame): Initialize new field.

	* dwarf2expr.h (struct dwarf_expr_context) <get_frame_cfa>: New

	field.

	* dwarf2expr.c (execute_stack_op) <DW_OP_call_frame_cfa>: New

	case.

	* dwarf2-frame.h (dwarf2_frame_cfa): Declare.

	* dwarf2-frame.c (no_get_frame_cfa): New function.

	(execute_stack_op): Initialize new field.

	(dwarf2_frame_cfa): New function.

[ Backported for Fedora Rawhide.  ]

--- ./gdb/dwarf2-frame.c	2009-06-12 11:12:51.000000000 +0200

+++ ./gdb/dwarf2-frame.c	2009-06-12 11:13:30.000000000 +0200

@@ -306,6 +306,13 @@ no_get_frame_base (void *baton, gdb_byte

 }

 static CORE_ADDR

+no_get_frame_cfa (void *baton)

+{

+  internal_error (__FILE__, __LINE__,

+		  _("Support for DW_OP_call_frame_cfa is unimplemented"));

+}

+

+static CORE_ADDR

 no_get_tls_address (void *baton, CORE_ADDR offset)

 {

   internal_error (__FILE__, __LINE__,

@@ -356,6 +363,7 @@ execute_stack_op (gdb_byte *exp, ULONGES

   ctx->read_reg = read_reg;

   ctx->read_mem = read_mem;

   ctx->get_frame_base = no_get_frame_base;

+  ctx->get_frame_cfa = no_get_frame_cfa;

   ctx->get_tls_address = no_get_tls_address;

   dwarf_expr_push (ctx, initial);

@@ -1221,6 +1229,13 @@ dwarf2_frame_base_address (struct frame_

   return cache->cfa;

 }

+CORE_ADDR

+dwarf2_frame_cfa (struct frame_info *this_frame)

+{

+  void *cache = NULL;

+  return dwarf2_frame_base_address (this_frame, &cache);

+}

+

 static const struct frame_base dwarf2_frame_base =

 {

   &dwarf2_frame_unwind,

--- ./gdb/dwarf2-frame.h	2009-01-03 06:57:51.000000000 +0100

+++ ./gdb/dwarf2-frame.h	2009-06-12 11:13:30.000000000 +0200

@@ -118,4 +118,8 @@ extern const struct frame_base *

 void dwarf2_frame_build_info (struct objfile *objfile);

+/* Compute the DWARF CFA for a frame.  */

+

+CORE_ADDR dwarf2_frame_cfa (struct frame_info *this_frame);

+

 #endif /* dwarf2-frame.h */

--- ./gdb/dwarf2expr.c	2009-06-12 11:12:51.000000000 +0200

+++ ./gdb/dwarf2expr.c	2009-06-12 11:13:44.000000000 +0200

@@ -697,6 +697,10 @@ execute_stack_op (struct dwarf_expr_cont

 	  }

 	  break;

+	case DW_OP_call_frame_cfa:

+	  result = (ctx->get_frame_cfa) (ctx->baton);

+	  break;

+

 	case DW_OP_GNU_push_tls_address:

 	  /* Variable is at a constant offset in the thread-local

 	  storage block into the objfile for the current thread and

--- ./gdb/dwarf2expr.h	2009-06-12 11:12:51.000000000 +0200

+++ ./gdb/dwarf2expr.h	2009-06-12 11:15:36.000000000 +0200

@@ -55,6 +55,9 @@ struct dwarf_expr_context

      expression evaluation is complete.  */

   void (*get_frame_base) (void *baton, gdb_byte **start, size_t *length);

+  /* Return the CFA for the frame.  */

+  CORE_ADDR (*get_frame_cfa) (void *baton);

+

   /* Return the thread-local storage address for

      DW_OP_GNU_push_tls_address.  */

   CORE_ADDR (*get_tls_address) (void *baton, CORE_ADDR offset);

--- ./gdb/dwarf2loc.c	2009-06-12 11:12:55.000000000 +0200

+++ ./gdb/dwarf2loc.c	2009-06-12 11:15:07.000000000 +0200

@@ -32,6 +32,7 @@

 #include "objfiles.h"

 #include "exceptions.h"

 #include "block.h"

+#include "dwarf2-frame.h"

 #include "elf/dwarf2.h"

 #include "dwarf2expr.h"

@@ -200,6 +201,13 @@ dwarf_expr_frame_base (void *baton, gdb_

 	   SYMBOL_PRINT_NAME (framefunc));

 }

+static CORE_ADDR

+dwarf_expr_frame_cfa (void *baton)

+{

+  struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;

+  return dwarf2_frame_cfa (debaton->frame);

+}

+

 /* Using the objfile specified in BATON, find the address for the

    current thread's thread-local storage with offset OFFSET.  */

 static CORE_ADDR

@@ -286,6 +294,7 @@ dwarf_expr_prep_ctx (struct frame_info *

   ctx->read_reg = dwarf_expr_read_reg;

   ctx->read_mem = dwarf_expr_read_mem;

   ctx->get_frame_base = dwarf_expr_frame_base;

+  ctx->get_frame_cfa = dwarf_expr_frame_cfa;

   ctx->get_tls_address = dwarf_expr_tls_address;

   ctx->get_object_address = dwarf_expr_object_address;

@@ -439,6 +448,15 @@ needs_frame_frame_base (void *baton, gdb

   nf_baton->needs_frame = 1;

 }

+/* CFA accesses require a frame.  */

+static CORE_ADDR

+needs_frame_frame_cfa (void *baton)

+{

+  struct needs_frame_baton *nf_baton = baton;

+  nf_baton->needs_frame = 1;

+  return 1;

+}

+

 /* Thread-local accesses do require a frame.  */

 static CORE_ADDR

 needs_frame_tls_address (void *baton, CORE_ADDR offset)

@@ -468,6 +486,7 @@ dwarf2_loc_desc_needs_frame (gdb_byte *d

   ctx->read_reg = needs_frame_read_reg;

   ctx->read_mem = needs_frame_read_mem;

   ctx->get_frame_base = needs_frame_frame_base;

+  ctx->get_frame_cfa = needs_frame_frame_cfa;

   ctx->get_tls_address = needs_frame_tls_address;

   dwarf_expr_eval (ctx, data, size);