[Bug gdb/25528] step will stopped at any "asm volatile" statement

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

https://sourceware.org/bugzilla/show_bug.cgi?id=25528

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Yibiao Yang from comment #1)
> In current version of GDB, statement with asm volatile will be skipped.
> 
> I was wondering that this is the default behavior of GDB.
> 

Compiling with gcc 9.3.1, and looking at the line info using readline -wL, I
get:
...
CU: small.c:

Line number    Starting address    View    Stmt
4            0x400492               x
5            0x40049c               x
6            0x4004a2               x
6            0x4004a8               x
8            0x4004aa               x
9            0x4004b8               x
9            0x4004c5               x
10           0x4004c9               x
6            0x4004c9       1       x
6            0x4004d4               x
12           0x4004db               x
14           0x4004df               x
14           0x4004e3               x
14           0x4004ed               x
14           0x4004f0               x
...

while we have:
...
$ cat -n small.c
     1  const signed char NM[] = {-1, 0, 1};
     2
     3  __attribute__((noinline)) void f(short delta)
     4  {
     5    short p = 2, s;
     6    for (s = 0; s < 2; s++)
     7    {
     8      p += delta;
     9      if (NM[p] == 0)
    10        asm volatile("");
    11    }
    12  }
    13
    14  void main(void) { f(-1); }
    15
...

So, the line with the asm stmt does have line info, but shares the address with
another entry with another line number.

Using this debugging session, we can see that we do visit the address, but show
line 6 instead of line 10:
...
(gdb) 
9           if (NM[p] == 0)
(gdb) p /x $pc
$1 = 0x4004b8
(gdb) s
6         for (s = 0; s < 2; s++)
(gdb) p /x $pc
$2 = 0x4004c9
(gdb) 
...
which I'd say is a valid interpretation of the line number info.

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