gdb/

        * frame.c (get_frame_id): Default to outer_frame_id if the this_id
        method does not supply an ID.  Assert that the result is not
        null_frame_id.
        (outer_frame_id): New.
        (frame_id_p): Accept outer_frame_id.
        (frame_id_eq): Allow outer_frame_id to be equal to itself.
        (frame_find_by_id): Revert previous local workarounds.
        (get_prev_frame_1): Adjust end-of-stack check to test outer_frame_id.
        * frame.h (null_frame_id, frame_id_p): Update comments.
        (outer_frame_id): Declare.
        * infrun.c (handle_inferior_event): Do not treat all steps from the
        outermost frame as subroutine calls.

        * libunwind-frame.c (libunwind_frame_this_id): Do not clear THIS_ID.
        * hppa-tdep.c (hppa_stub_frame_this_id): Likewise.
        * ia64-tdep.c (ia64_frame_this_id): Likewise.
        (ia64_libunwind_frame_this_id, ia64_libunwind_sigtramp_frame_this_id):
        Use outer_frame_id instead of null_frame_id.
        * amd64obsd-tdep.c (amd64obsd_trapframe_cache): Use outer_frame_id.
        * i386obsd-tdep.c (i386obsd_trapframe_cache): Likewise.
        * inline-frame.c (inline_frame_this_id): Refuse outer_frame_id.
        * thread.c (restore_selected_frame): Update comment and remove
        frame_id_p check.

        gdb/doc/
        * gdbint.texinfo (Unwinding the Frame ID): Reference outer_frame_id.

13 files changed, 93 insertions, 30 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 80d33ac..a1e66e6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,29 @@
+2009-09-13  Daniel Jacobowitz  <dan@codesourcery.com>
+
+	* frame.c (get_frame_id): Default to outer_frame_id if the this_id
+	method does not supply an ID.  Assert that the result is not
+	null_frame_id.
+	(outer_frame_id): New.
+	(frame_id_p): Accept outer_frame_id.
+	(frame_id_eq): Allow outer_frame_id to be equal to itself.
+	(frame_find_by_id): Revert previous local workarounds.
+	(get_prev_frame_1): Adjust end-of-stack check to test outer_frame_id.
+	* frame.h (null_frame_id, frame_id_p): Update comments.
+	(outer_frame_id): Declare.
+	* infrun.c (handle_inferior_event): Do not treat all steps from the
+	outermost frame as subroutine calls.
+
+	* libunwind-frame.c (libunwind_frame_this_id): Do not clear THIS_ID.
+	* hppa-tdep.c (hppa_stub_frame_this_id): Likewise.
+	* ia64-tdep.c (ia64_frame_this_id): Likewise.
+	(ia64_libunwind_frame_this_id, ia64_libunwind_sigtramp_frame_this_id):
+	Use outer_frame_id instead of null_frame_id.
+	* amd64obsd-tdep.c (amd64obsd_trapframe_cache): Use outer_frame_id.
+	* i386obsd-tdep.c (i386obsd_trapframe_cache): Likewise.
+	* inline-frame.c (inline_frame_this_id): Refuse outer_frame_id.
+	* thread.c (restore_selected_frame): Update comment and remove
+	frame_id_p check.
+
 2009-09-11  Doug Evans  <dje@google.com>
 
 	* dwarf2expr.c (execute_stack_op, case DW_OP_piece): Delete unused
diff --git a/gdb/amd64obsd-tdep.c b/gdb/amd64obsd-tdep.c
index 1938bdd..ed57cb8 100644
--- a/gdb/amd64obsd-tdep.c
+++ b/gdb/amd64obsd-tdep.c
@@ -380,7 +380,7 @@ amd64obsd_trapframe_cache (struct frame_info *this_frame, void **this_cache)
   if ((cs & I386_SEL_RPL) == I386_SEL_UPL)
     {
       /* Trap from user space; terminate backtrace.  */
-      trad_frame_set_id (cache, null_frame_id);
+      trad_frame_set_id (cache, outer_frame_id);
     }
   else
     {
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 595bbe2..8a9bb7b 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,7 @@
+2009-09-13  Daniel Jacobowitz  <dan@codesourcery.com>
+
+	* gdbint.texinfo (Unwinding the Frame ID): Reference outer_frame_id.
+
 2009-09-10  Michael Snyder  <msnyder@vmware.com>
 
 	* gdb.texinfo (qSupported): Mention new ReverseContinue and
diff --git a/gdb/doc/gdbint.texinfo b/gdb/doc/gdbint.texinfo
index e706caa..c2be3f7 100644
--- a/gdb/doc/gdbint.texinfo
+++ b/gdb/doc/gdbint.texinfo
@@ -2042,9 +2042,17 @@ address as its caller.  On some platforms, a third address is part of
 the ID to further disambiguate frames---for instance, on IA-64
 the separate register stack address is included in the ID.
 
-An invalid frame ID (@code{null_frame_id}) returned from the
+An invalid frame ID (@code{outer_frame_id}) returned from the
 @code{this_id} method means to stop unwinding after this frame.
 
+@code{null_frame_id} is another invalid frame ID which should be used
+when there is no frame.  For instance, certain breakpoints are attached
+to a specific frame, and that frame is identified through its frame ID
+(we use this to implement the "finish" command).  Using
+@code{null_frame_id} as the frame ID for a given breakpoint means
+that the breakpoint is not specific to any frame.  The @code{this_id}
+method should never return @code{null_frame_id}.
+
 @section Unwinding Registers
 
 Each unwinder includes a @code{prev_register} method.  This method
diff --git a/gdb/frame.c b/gdb/frame.c
index 9ca69bf..7932b48 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -324,7 +324,10 @@ get_frame_id (struct frame_info *fi)
       if (fi->unwind == NULL)
 	fi->unwind = frame_unwind_find_by_frame (fi, &fi->prologue_cache);
       /* Find THIS frame's ID.  */
+      /* Default to outermost if no ID is found.  */
+      fi->this_id.value = outer_frame_id;
       fi->unwind->this_id (fi, &fi->prologue_cache, &fi->this_id.value);
+      gdb_assert (frame_id_p (fi->this_id.value));
       fi->this_id.p = 1;
       if (frame_debug)
 	{
@@ -364,6 +367,7 @@ frame_unwind_caller_id (struct frame_info *next_frame)
 }
 
 const struct frame_id null_frame_id; /* All zeros.  */
+const struct frame_id outer_frame_id = { 0, 0, 0, 0, 0, 1, 0 };
 
 struct frame_id
 frame_id_build_special (CORE_ADDR stack_addr, CORE_ADDR code_addr,
@@ -405,6 +409,9 @@ frame_id_p (struct frame_id l)
   int p;
   /* The frame is valid iff it has a valid stack address.  */
   p = l.stack_addr_p;
+  /* outer_frame_id is also valid.  */
+  if (!p && memcmp (&l, &outer_frame_id, sizeof (l)) == 0)
+    p = 1;
   if (frame_debug)
     {
       fprintf_unfiltered (gdb_stdlog, "{ frame_id_p (l=");
@@ -427,7 +434,14 @@ int
 frame_id_eq (struct frame_id l, struct frame_id r)
 {
   int eq;
-  if (!l.stack_addr_p || !r.stack_addr_p)
+  if (!l.stack_addr_p && l.special_addr_p && !r.stack_addr_p && r.special_addr_p)
+    /* The outermost frame marker is equal to itself.  This is the
+       dodgy thing about outer_frame_id, since between execution steps
+       we might step into another function - from which we can't
+       unwind either.  More thought required to get rid of
+       outer_frame_id.  */
+    eq = 1;
+  else if (!l.stack_addr_p || !r.stack_addr_p)
     /* Like a NaN, if either ID is invalid, the result is false.
        Note that a frame ID is invalid iff it is the null frame ID.  */
     eq = 0;
@@ -1425,7 +1439,7 @@ get_prev_frame_1 (struct frame_info *this_frame)
      unwind to the prev frame.  Be careful to not apply this test to
      the sentinel frame.  */
   this_id = get_frame_id (this_frame);
-  if (this_frame->level >= 0 && !frame_id_p (this_id))
+  if (this_frame->level >= 0 && frame_id_eq (this_id, outer_frame_id))
     {
       if (frame_debug)
 	{
diff --git a/gdb/frame.h b/gdb/frame.h
index 611c6d3..994b529 100644
--- a/gdb/frame.h
+++ b/gdb/frame.h
@@ -142,9 +142,14 @@ struct frame_id
 
 /* Methods for constructing and comparing Frame IDs.  */
 
-/* For convenience.  All fields are zero.  */
+/* For convenience.  All fields are zero.  This means "there is no frame".  */
 extern const struct frame_id null_frame_id;
 
+/* This means "there is no frame ID, but there is a frame".  It should be
+   replaced by best-effort frame IDs for the outermost frame, somehow.
+   The implementation is only special_addr_p set.  */
+extern const struct frame_id outer_frame_id;
+
 /* Flag to control debugging.  */
 
 extern int frame_debug;
@@ -170,7 +175,8 @@ extern struct frame_id frame_id_build_special (CORE_ADDR stack_addr,
 extern struct frame_id frame_id_build_wild (CORE_ADDR stack_addr);
 
 /* Returns non-zero when L is a valid frame (a valid frame has a
-   non-zero .base).  */
+   non-zero .base).  The outermost frame is valid even without an
+   ID.  */
 extern int frame_id_p (struct frame_id l);
 
 /* Returns non-zero when L is a valid frame representing an inlined
diff --git a/gdb/hppa-tdep.c b/gdb/hppa-tdep.c
index 072e687..03aa6c6 100644
--- a/gdb/hppa-tdep.c
+++ b/gdb/hppa-tdep.c
@@ -2427,8 +2427,6 @@ hppa_stub_frame_this_id (struct frame_info *this_frame,
 
   if (info)
     *this_id = frame_id_build (info->base, get_frame_func (this_frame));
-  else
-    *this_id = null_frame_id;
 }
 
 static struct value *
diff --git a/gdb/i386obsd-tdep.c b/gdb/i386obsd-tdep.c
index 8621838..c33a24e 100644
--- a/gdb/i386obsd-tdep.c
+++ b/gdb/i386obsd-tdep.c
@@ -376,7 +376,7 @@ i386obsd_trapframe_cache (struct frame_info *this_frame, void **this_cache)
   if ((cs & I386_SEL_RPL) == I386_SEL_UPL)
     {
       /* Trap from user space; terminate backtrace.  */
-      trad_frame_set_id (cache, null_frame_id);
+      trad_frame_set_id (cache, outer_frame_id);
     }
   else
     {
diff --git a/gdb/ia64-tdep.c b/gdb/ia64-tdep.c
index bc72e40..674204a 100644
--- a/gdb/ia64-tdep.c
+++ b/gdb/ia64-tdep.c
@@ -1774,9 +1774,7 @@ ia64_frame_this_id (struct frame_info *this_frame, void **this_cache,
     ia64_frame_cache (this_frame, this_cache);
 
   /* If outermost frame, mark with null frame id.  */
-  if (cache->base == 0)
-    (*this_id) = null_frame_id;
-  else
+  if (cache->base != 0)
     (*this_id) = frame_id_build_special (cache->base, cache->pc, cache->bsp);
   if (gdbarch_debug >= 1)
     fprintf_unfiltered (gdb_stdlog,
@@ -2790,15 +2788,14 @@ ia64_libunwind_frame_this_id (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 frame_id id;
+  struct frame_id id = outer_frame_id;
   char buf[8];
   CORE_ADDR bsp;
 
-
   libunwind_frame_this_id (this_frame, this_cache, &id);
-  if (frame_id_eq (id, null_frame_id))
+  if (frame_id_eq (id, outer_frame_id))
     {
-      (*this_id) = null_frame_id;
+      (*this_id) = outer_frame_id;
       return;
     }
 
@@ -2923,13 +2920,13 @@ ia64_libunwind_sigtramp_frame_this_id (struct frame_info *this_frame,
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   char buf[8];
   CORE_ADDR bsp;
-  struct frame_id id;
+  struct frame_id id = outer_frame_id;
   CORE_ADDR prev_ip;
 
   libunwind_frame_this_id (this_frame, this_cache, &id);
-  if (frame_id_eq (id, null_frame_id))
+  if (frame_id_eq (id, outer_frame_id))
     {
-      (*this_id) = null_frame_id;
+      (*this_id) = outer_frame_id;
       return;
     }
 
diff --git a/gdb/infrun.c b/gdb/infrun.c
index c907635..a6ca2e3 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -3796,10 +3796,22 @@ infrun: not switching back to stepped thread, it has vanished\n");
      NOTE: frame_id_eq will never report two invalid frame IDs as
      being equal, so to get into this block, both the current and
      previous frame must have valid frame IDs.  */
+  /* The outer_frame_id check is a heuristic to detect stepping
+     through startup code.  If we step over an instruction which
+     sets the stack pointer from an invalid value to a valid value,
+     we may detect that as a subroutine call from the mythical
+     "outermost" function.  This could be fixed by marking
+     outermost frames as !stack_p,code_p,special_p.  Then the
+     initial outermost frame, before sp was valid, would
+     have code_addr == &_start.  See the commend in frame_id_eq
+     for more.  */
   if (!frame_id_eq (get_stack_frame_id (frame),
 		    ecs->event_thread->step_stack_frame_id)
-      && frame_id_eq (frame_unwind_caller_id (frame),
-		      ecs->event_thread->step_stack_frame_id))
+      && (frame_id_eq (frame_unwind_caller_id (get_current_frame ()),
+		       ecs->event_thread->step_stack_frame_id)
+	  && (!frame_id_eq (ecs->event_thread->step_stack_frame_id,
+			    outer_frame_id)
+	      || step_start_function != find_pc_function (stop_pc))))
     {
       CORE_ADDR real_stop_pc;
 
diff --git a/gdb/inline-frame.c b/gdb/inline-frame.c
index 731d3ad..0e6dae3 100644
--- a/gdb/inline-frame.c
+++ b/gdb/inline-frame.c
@@ -148,6 +148,10 @@ inline_frame_this_id (struct frame_info *this_frame,
      frame").  This will take work.  */
   gdb_assert (frame_id_p (*this_id));
 
+  /* For now, require we don't match outer_frame_id either (see
+     comment above).  */
+  gdb_assert (!frame_id_eq (*this_id, outer_frame_id));
+
   /* Future work NOTE: Alexandre Oliva applied a patch to GCC 4.3
      which generates DW_AT_entry_pc for inlined functions when
      possible.  If this attribute is available, we should use it
diff --git a/gdb/libunwind-frame.c b/gdb/libunwind-frame.c
index b1896dc..921d00e 100644
--- a/gdb/libunwind-frame.c
+++ b/gdb/libunwind-frame.c
@@ -278,8 +278,6 @@ libunwind_frame_this_id (struct frame_info *this_frame, void **this_cache,
 
   if (cache != NULL)
     (*this_id) = frame_id_build (cache->base, cache->func_addr);
-  else
-    (*this_id) = null_frame_id;
 }
 
 struct value *
diff --git a/gdb/thread.c b/gdb/thread.c
index a7ac3c8..55b4b96 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -885,15 +885,11 @@ restore_selected_frame (struct frame_id a_frame_id, int frame_level)
   frame = find_relative_frame (get_current_frame (), &count);
   if (count == 0
       && frame != NULL
-      /* Either the frame ids match, of they're both invalid.  The
-	 latter case is not failsafe, but since it's highly unlikely
+      /* The frame ids must match - either both valid or both outer_frame_id.
+	 The latter case is not failsafe, but since it's highly unlikely
 	 the search by level finds the wrong frame, it's 99.9(9)% of
 	 the time (for all practical purposes) safe.  */
-      && (frame_id_eq (get_frame_id (frame), a_frame_id)
-	  /* Note: could be better to check every frame_id
-	     member for equality here.  */
-	  || (!frame_id_p (get_frame_id (frame))
-	      && !frame_id_p (a_frame_id))))
+      && frame_id_eq (get_frame_id (frame), a_frame_id))
     {
       /* Cool, all is fine.  */
       select_frame (frame);