[Bug symtab/29236] [gdb] make viewpoints at same address explicit

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29236

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
                 CC|                            |vries at gcc dot gnu.org
            Summary|wrong mapping between       |[gdb] make viewpoints at
                   |address and source line     |same address explicit

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
The problem is that while cleverly showing 2 different debug states for the
same pc (1. call to inlined code, 2. inlined code) we otherwise don't make
explicit that we do this, causing user confusion.

Using this sort of annotation (not sure about the logic, but works for the
example):
...
diff --git a/gdb/stack.c b/gdb/stack.c
index 4a3e7e4ff00..18291f139d7 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -1353,7 +1353,13 @@ print_frame (struct ui_out *uiout,
        {
          annotate_frame_address ();
          if (pc_p)
-           print_pc (uiout, gdbarch, frame, pc);
+           {
+             int n = frame_inlined_callees (frame);
+             int total = n + (get_frame_type (frame) == INLINE_FRAME ? 1 : 0);
+             if (total != 0)
+               gdb_printf ("VIEWPOINT(%d/%d)@", total - n + 1, total + 1);
+             print_pc (uiout, gdbarch, frame, pc);
+           }
          else
            uiout->field_string ("addr", "<unavailable>",
                                 metadata_style.style ());
...
we get:
...
$ gdb -q -batch -iex "set trace-commands on" a.out \
    -ex start \
    -ex step \
    -ex "bt -frame-info location-and-address" \
    -ex step \
    -ex "bt -frame-info location-and-address" 
+start
Temporary breakpoint 1 at 0x410080: file small.c, line 10.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Temporary breakpoint 1, main (argc=1, argv=0xffffffffe928) at small.c:10
10        pa = &a;
+step
13        access (pa);
+bt -frame-info location-and-address
#0  VIEWPOINT(1/2)@0x000000000041008c in main (argc=<optimized out>,
argv=0xffffffffe928) at small.c:13
+step
VIEWPOINT(2/2)@0x000000000041008c in access (ptr=<optimized out>) at small.c:4
4       void access (volatile char *ptr) { *ptr = 'x'; }
+bt -frame-info location-and-address
#0  VIEWPOINT(2/2)@0x000000000041008c in access (ptr=<optimized out>) at
small.c:4
#1  VIEWPOINT(1/2)@0x000000000041008c in main (argc=<optimized out>,
argv=0xffffffffe928) at small.c:13
...
shows in an in-your-face fashion that tricks are being played with the address.

[ We're going to need something similar for location views, the same confusion
is likely to show up once we start supporting that. ]

Changing into an enhancement, updating $subject.

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