[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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