Re: [patch] circ.exp

[Pedro Alves <palves at redhat dot com>]

On 04/17/2013 05:06 PM, Abid, Hafiz wrote:
> 
>> > 4) Many tests were expecting current stack frame to be printed as result of
>> > tfind command e.g. "#0  func9 .*".  But this only happens when traceframe_number
>> > is -1.  In the following code, old_frame_id equal to current frame id unless
>> > traceframe_number < 0.
>> >
>>
>> I'm confused.  Does the tfind in question switch to a different
>> frame or not?
> I have observed that location is only printed first time we give tfind command (or give it after doing a tfind none).
> If you see the example session below, you will see that 'tfind start' prints the following line.
> #0  func0 () at ../.././../git/gdb/testsuite/gdb.trace/circ.c:28
> 
> But next tfind does not print any such line. The test was assuming the presence of this line every time. I am not sure what is expected behavior is though.
> 
> (gdb) tstart
> (gdb) info tracepoints
> Num     Type           Disp Enb Address    What
> 1       tracepoint     keep y   0x080483b7 in func0
>                                            at ../.././../git/gdb/testsuite/gdb.trace/circ.c:28
>         collect testload
>     installed on target
> 2       tracepoint     keep y   0x080483bc in func1
>                                            at ../.././../git/gdb/testsuite/gdb.trace/circ.c:32
>         collect testload
>     installed on target
> (gdb) c
> Continuing.
> 
> Breakpoint 3, end () at ../.././../git/gdb/testsuite/gdb.trace/circ.c:72
> 72    }
> (gdb) tstop
> (gdb) tfind start
> Found trace frame 0, tracepoint 1
> #0  func0 () at ../.././../git/gdb/testsuite/gdb.trace/circ.c:28
> 28    }
> (gdb) tfind
> Found trace frame 1, tracepoint 2
> 32    }
> (gdb)

I see.  The issue is that when haven't collected any registers in the
the tracepoint (collect $regs), we end up with a frames that are
un-unwindable (UNWIND_UNAVAILABLE).  All frames in that case have the same
id (outer_frame_id), even if they represent different functions.  I started
out with a local fix in tfind_1, but that got ugly quick.  I think we
should fix this in the frame machinery itself.  Here's a WIP patch for that.
It makes us build a frame id that represents a function, with an <unavailable>
stack address.  I haven't thought every detail through, but I think it's
on the right path.

---

 gdb/frame.c |   54 ++++++++++++++++++++++++++++++++++++++++++++++--------
 gdb/frame.h |    8 +++++---
 2 files changed, 51 insertions(+), 11 deletions(-)

diff --git a/gdb/frame.c b/gdb/frame.c
index 8d4e2c8..c62202c 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -47,6 +47,8 @@
 static struct frame_info *get_prev_frame_1 (struct frame_info *this_frame);
 static struct frame_info *get_prev_frame_raw (struct frame_info *this_frame);
 
+static struct frame_id frame_id_build_unavailable_stack (CORE_ADDR code_addr);
+
 /* We keep a cache of stack frames, each of which is a "struct
    frame_info".  The innermost one gets allocated (in
    wait_for_inferior) each time the inferior stops; current_frame
@@ -210,7 +212,9 @@ show_backtrace_limit (struct ui_file *file, int from_tty,
 static void
 fprint_field (struct ui_file *file, const char *name, int p, CORE_ADDR addr)
 {
-  if (p)
+  if (p < 0)
+    fprintf_unfiltered (file, "%s=<unavailable>", name);
+  else if (p > 0)
     fprintf_unfiltered (file, "%s=%s", name, hex_string (addr));
   else
     fprintf_unfiltered (file, "!%s", name);
@@ -333,10 +337,27 @@ get_frame_id (struct frame_info *fi)
       /* Find the unwinder.  */
       if (fi->unwind == NULL)
 	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);
+
+      fi->stop_reason = fi->unwind->stop_reason (fi,&fi->prologue_cache);
+
+      /* Find THIS frame's ID.  If the stack is unavailable, build a
+	 frame id that identifies the function (and that only matches
+	 equal with another stackless frame id of the same
+	 function).  */
+      if (fi->stop_reason == UNWIND_UNAVAILABLE)
+	{
+	  CORE_ADDR pc;
+
+	  pc = get_frame_func (fi);
+	  fi->this_id.value = frame_id_build_unavailable_stack (pc);
+	}
+      else
+	{
+	  /* 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)
@@ -394,6 +415,22 @@ frame_id_build_special (CORE_ADDR stack_addr, CORE_ADDR code_addr,
   return id;
 }
 
+/* Construct a frame ID representing a frame where the stack address
+   is unavailable (but exists).  The first parameter is the frame's
+   constant code address (typically the entry point).  The special
+   identifier address is set to indicate a wild card.  */
+
+static struct frame_id
+frame_id_build_unavailable_stack (CORE_ADDR code_addr)
+{
+  struct frame_id id = null_frame_id;
+
+  id.stack_addr_p = -1;
+  id.code_addr = code_addr;
+  id.code_addr_p = 1;
+  return id;
+}
+
 struct frame_id
 frame_id_build (CORE_ADDR stack_addr, CORE_ADDR code_addr)
 {
@@ -461,7 +498,7 @@ frame_id_eq (struct frame_id l, struct frame_id r)
     /* 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;
-  else if (l.stack_addr != r.stack_addr)
+  else if (l.stack_addr_p != r.stack_addr_p || l.stack_addr != r.stack_addr)
     /* If .stack addresses are different, the frames are different.  */
     eq = 0;
   else if (l.code_addr_p && r.code_addr_p && l.code_addr != r.code_addr)
@@ -528,8 +565,9 @@ frame_id_inner (struct gdbarch *gdbarch, struct frame_id l, struct frame_id r)
 {
   int inner;
 
-  if (!l.stack_addr_p || !r.stack_addr_p)
-    /* Like NaN, any operation involving an invalid ID always fails.  */
+  if (l.stack_addr_p != 1 || r.stack_addr_p != 1)
+    /* Like NaN, any operation involving an invalid ID always fails.
+       Likewise if either ID has an unavailable stack address.  */
     inner = 0;
   else if (l.artificial_depth > r.artificial_depth
 	   && l.stack_addr == r.stack_addr
diff --git a/gdb/frame.h b/gdb/frame.h
index 31b9cb7..66226d2 100644
--- a/gdb/frame.h
+++ b/gdb/frame.h
@@ -97,8 +97,10 @@ struct frame_id
      function pointer register or stack pointer register.  They are
      wrong.
 
-     This field is valid only if stack_addr_p is true.  Otherwise, this
-     frame represents the null frame.  */
+     This field is valid only if stack_addr_p is positive.  If 0, this
+     frame represents the null frame.  If -1, we don't have the stack
+     address available -- e.g., we're inspecting a trace frame where
+     enough registers hadn't been collected.  */
   CORE_ADDR stack_addr;
 
   /* The frame's code address.  This shall be constant through out the
@@ -129,7 +131,7 @@ struct frame_id
   CORE_ADDR special_addr;
 
   /* Flags to indicate the above fields have valid contents.  */
-  unsigned int stack_addr_p : 1;
+  int stack_addr_p : 2;
   unsigned int code_addr_p : 1;
   unsigned int special_addr_p : 1;