[Bug symtab/29236] New: wrong mapping between address and source line

[Bug symtab/29236] New: wrong mapping between address and source line

[yangyibiao at nju dot edu.cn]

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

            Bug ID: 29236
           Summary: wrong mapping between address and source line
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: yangyibiao at nju dot edu.cn
  Target Milestone: ---

$ gcc --version
gcc (GCC) 13.0.0 20220608 (experimental)

$ gdb --version
GNU gdb (GDB) 13.0.50.20220608-git

$ cat small.c
char *pa;
char *pb;

void access (volatile char *ptr) { *ptr = 'x'; }

int main (int argc, char **argv)
{
  char a, b;

  pa = &a;
  pb = &b;

  access (pa);
  access (pb);

  return 0;
}

$ gcc -O2 -g small.c; gdb -q a.out
Reading symbols from a.out...
(gdb) b main
Breakpoint 1 at 0x401020: file small.c, line 10.
(gdb) r
Starting program: /root/a.out

Breakpoint 1, main (argc=1, argv=0x7fffffffe4f8) at small.c:10
10        pa = &a;
(gdb) s
13        access (pa);
(gdb) bt -frame-info location-and-address
#0  0x0000000000401025 in main (argc=1, argv=0x7fffffffe4f8) at small.c:13
(gdb) maint info line-table
objfile: /root/a.out ((struct objfile *) 0x20d7c60)
compunit_symtab: small.c ((struct compunit_symtab *) 0x216ac40)
symtab: /root/small.c ((struct symtab *) 0x216acc0)
linetable: ((struct linetable *) 0x21cb060):
INDEX  LINE   ADDRESS            IS-STMT PROLOGUE-END
0      7      0x0000000000401020 Y
1      8      0x0000000000401020 Y
2      10     0x0000000000401020 Y
3      10     0x0000000000401020
4      4      0x0000000000401025
5      10     0x000000000040102a
6      11     0x0000000000401031 Y
7      11     0x0000000000401031
8      13     0x000000000040103d Y
9      4      0x000000000040103d Y
10     4      0x000000000040103d Y
11     4      0x000000000040103d
12     14     0x000000000040103d Y
13     4      0x000000000040103d Y
14     4      0x000000000040103d Y
15     17     0x000000000040103d
16     4      0x000000000040103f
17     4      0x0000000000401044
18     16     0x0000000000401044 Y
19     17     0x0000000000401044
20     END    0x0000000000401045 Y
21     4      0x0000000000401140 Y
22     4      0x0000000000401140 Y
23     4      0x0000000000401140
24     4      0x0000000000401143
25     END    0x0000000000401144 Y

(gdb)


======================================================================
= As we can find from the line-table, line 4 is only maps to the address of
0x0000000000401025 and the "IS-STMT" for line 13 is "Y"(yes). 
= However, the backtrace reports that this address of 0x0000000000401025 is at
line 13 as "#0  0x0000000000401025 in main (argc=1, argv=0x7fffffffe4f8) at
small.c:13". 
= I was wondering that this might be a gdb issue. 
======================================================================

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[Bug symtab/29236] wrong mapping between address and source line

[yangyibiao at nju dot edu.cn]

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

Yibiao Yang <yangyibiao at nju dot edu.cn> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org

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[Bug symtab/29236] wrong mapping between address and source line

[yangyibiao at nju dot edu.cn]

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

Yibiao Yang <yangyibiao at nju dot edu.cn> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |yangyibiao at nju dot edu.cn

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[Bug symtab/29236] wrong mapping between address and source line

[tromey at sourceware dot org]

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

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-06-12
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
Looks like a bug.

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[Bug symtab/29236] wrong mapping between address and source line

[ssbssa at sourceware dot org]

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

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ssbssa at sourceware dot org

--- Comment #2 from Hannes Domani <ssbssa at sourceware dot org> ---
As far as I can tell this is part of gdb's magic to make debugging of inline
functions easier to follow.

I've different addresses, but I get a similar result:
```
(gdb) s
13        access (pa);
(gdb) bt -frame-info location-and-address
#0  0x000000013f96253e in main (argc=<optimized out>, argv=<optimized out>) at
gdb-29236.c:13
(gdb) maint info line-table gdb-29236.c
INDEX  LINE   REL-ADDRESS        UNREL-ADDRESS      IS-STMT PROLOGUE-END
...
12     4      0x000000013f96253e 0x000000014000253e
```

And then, I step again:
```
(gdb) s
0x000000013f96253e in access (ptr=<optimized out>) at gdb-29236.c:4
4       void access (volatile char *ptr) { *ptr = 'x'; }
(gdb) bt -frame-info location-and-address
#0  0x000000013f96253e in access (ptr=<optimized out>) at gdb-29236.c:4
#1  0x000000013f96253e in main (argc=<optimized out>, argv=<optimized out>) at
gdb-29236.c:13
```

The address stays the same, so gdb didn't really step, but just faked this for
the user.

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

[vries at gcc dot gnu.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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[Bug symtab/29236] [gdb] make viewpoints at same address explicit

[sam at gentoo dot org]

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

Sam James <sam at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sam at gentoo dot org

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