2009-07-12 Michael Snyder <msnyder@vmware.com>

	* i386-tdep.c: Add a frame unwinder for function epilogues.
	(i386_in_function_epilogue_p): New function.
	(i386_epilogue_frame_sniffer): New function.
	(i386_epilogue_frame_cache): New function.
	(i386_epilogue_frame_this_id): New function.
	(i386_epilogue_frame_unwind): New struct frame_unwind.
	(i386_gdbarch_init): Hook the new unwinder.

1 files changed, 93 insertions, 1 deletions

diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
index bf3a844..2d73785 100644
--- a/gdb/i386-tdep.c
+++ b/gdb/i386-tdep.c
@@ -1487,6 +1487,89 @@ static const struct frame_unwind i386_frame_unwind =
   NULL,
   default_frame_sniffer
 };
+
+/* Normal frames, but in a function epilogue.  */
+
+/* The epilogue is defined here as the 'ret' instruction, which will
+   follow any instruction such as 'leave' or 'pop %ebp' that destroys
+   the function's stack frame.  */
+
+static int
+i386_in_function_epilogue_p (struct gdbarch *gdbarch, CORE_ADDR pc)
+{
+  gdb_byte insn;
+
+  if (target_read_memory (pc, &insn, 1))
+    return 0;	/* Can't read memory at pc.  */
+
+  if (insn != 0xc3)	/* 'ret' instruction.  */
+    return 0;
+
+  return 1;
+}
+
+static int
+i386_epilogue_frame_sniffer (const struct frame_unwind *self,
+			     struct frame_info *this_frame,
+			     void **this_prologue_cache)
+{
+  if (frame_relative_level (this_frame) == 0)
+    return i386_in_function_epilogue_p (get_frame_arch (this_frame),
+					get_frame_pc (this_frame));
+  else
+    return 0;
+}
+
+static struct i386_frame_cache *
+i386_epilogue_frame_cache (struct frame_info *this_frame, void **this_cache)
+{
+  struct gdbarch *gdbarch = get_frame_arch (this_frame);
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+  struct i386_frame_cache *cache;
+  gdb_byte buf[4];
+
+  if (*this_cache)
+    return *this_cache;
+
+  cache = i386_alloc_frame_cache ();
+  *this_cache = cache;
+
+  /* Cache base will be %esp plus cache->sp_offset (-4).  */
+  get_frame_register (this_frame, I386_ESP_REGNUM, buf);
+  cache->base = extract_unsigned_integer (buf, 4, 
+					  byte_order) + cache->sp_offset;
+
+  /* Cache pc will be the frame func.  */
+  cache->pc = get_frame_pc (this_frame);
+
+  /* The saved %esp will be at cache->base plus 8.  */
+  cache->saved_sp = cache->base + 8;
+
+  /* The saved %eip will be at cache->base plus 4.  */
+  cache->saved_regs[I386_EIP_REGNUM] = cache->base + 4;
+
+  return cache;
+}
+
+static void
+i386_epilogue_frame_this_id (struct frame_info *this_frame,
+			     void **this_cache,
+			     struct frame_id *this_id)
+{
+  struct i386_frame_cache *cache = i386_epilogue_frame_cache (this_frame,
+							      this_cache);
+
+  (*this_id) = frame_id_build (cache->base + 8, cache->pc);
+}
+
+static const struct frame_unwind i386_epilogue_frame_unwind =
+{
+  NORMAL_FRAME,
+  i386_epilogue_frame_this_id,
+  i386_frame_prev_register,
+  NULL, 
+  i386_epilogue_frame_sniffer
+};
 
 
 /* Signal trampolines.  */
@@ -5329,7 +5412,15 @@ i386_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   /* Helper for function argument information.  */
   set_gdbarch_fetch_pointer_argument (gdbarch, i386_fetch_pointer_argument);
 
-  /* Hook in the DWARF CFI frame unwinder.  */
+  /* Hook the function epilogue frame unwinder.  This unwinder is
+     appended to the list first, so that it supercedes the Dwarf
+     unwinder in function epilogues (where the Dwarf unwinder
+     currently fails).  */
+  frame_unwind_append_unwinder (gdbarch, &i386_epilogue_frame_unwind);
+
+  /* Hook in the DWARF CFI frame unwinder.  This unwinder is appended
+     to the list before the prologue-based unwinders, so that Dwarf
+     CFI info will be used if it is available.  */
   dwarf2_append_unwinders (gdbarch);
 
   frame_base_set_default (gdbarch, &i386_frame_base);
@@ -5337,6 +5428,7 @@ i386_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   /* Hook in ABI-specific overrides, if they have been registered.  */
   gdbarch_init_osabi (info, gdbarch);
 
+  /* Hook in the legacy prologue-based unwinders last (fallback).  */
   frame_unwind_append_unwinder (gdbarch, &i386_sigtramp_frame_unwind);
   frame_unwind_append_unwinder (gdbarch, &i386_frame_unwind);