[Bug c/52160] New: gdb ignores line "bar: if(foo)goto bar;"

[Bug c/52160] New: gdb ignores line "bar: if(foo)goto bar;"

[safinaskar at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52160

             Bug #: 52160
           Summary: gdb ignores line "bar: if(foo)goto bar;"
    Classification: Unclassified
           Product: gcc
           Version: 4.4.5
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: safinaskar@mail.ru


foo.c:
-----------------------------------
#include <stdio.h>

int main()
{
        int foo;
        printf("Enter foo: ");
        scanf("%d", &foo);
bar:    if(foo)goto bar;
        return 0;
}
-----------------------------------
0:~# gcc -g foo.c
0:~# gdb a.out
GNU gdb (GDB) 7.0.1-debian
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /root/a.out...done.
(gdb) start
Temporary breakpoint 1 at 0x804842d: file foo.c, line 6.
Starting program: /root/a.out 

Temporary breakpoint 1, main () at foo.c:6
6               printf("Enter foo: ");
(gdb) n
7               scanf("%d", &foo);
(gdb) 
Enter foo: 0
9               return 0;
(gdb) q
A debugging session is active.

        Inferior 1 [process 21382] will be killed.

Quit anyway? (y or n) y
-----------------------------------
But gdb must say:

6               printf("Enter foo: ");
(gdb) n
7               scanf("%d", &foo);
(gdb) 
Enter foo: 0
8       bar:    if(foo)goto bar; 
(gdb) 
9               return 0;
-----------------------------------
0:~# gdb a.out
GNU gdb (GDB) 7.0.1-debian
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /root/a.out...done.
(gdb) start
Temporary breakpoint 1 at 0x804842d: file foo.c, line 6.
Starting program: /root/a.out 

Temporary breakpoint 1, main () at foo.c:6
6               printf("Enter foo: ");
(gdb) n
7               scanf("%d", &foo);
(gdb) 
Enter foo: 1
^C
Program received signal SIGINT, Interrupt.
0x08048458 in main () at foo.c:8
8       bar:    if(foo)goto bar;
(gdb) q
A debugging session is active.

        Inferior 1 [process 21399] will be killed.

Quit anyway? (y or n) y
-----------------------------------
But gdb must say:

6               printf("Enter foo: ");
(gdb) n
7               scanf("%d", &foo);
(gdb) 
Enter foo: 1
8       bar:    if(foo)goto bar; 
(gdb) 
^C
-----------------------------------
0:~# uname -a
Linux debian 2.6.32-5-686 #1 SMP Sat Oct 30 22:47:19 UTC 2010 i686 GNU/Linux
0:~# gcc -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.5-8'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.4 --enable-shared --enable-multiarch
--enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-targets=all --with-arch-32=i586 --with-tune=generic
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.4.5 (Debian 4.4.5-8)

Bug moved from http://sourceware.org/bugzilla/show_bug.cgi?id=12257

[Bug debug/52160] gdb ignores line "bar: if(foo)goto bar;"

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52160

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-02-07 21:44:42 UTC ---
Here is what GCC produces:
    .loc 1 7 0
    leaq    -4(%rbp), %rax
    movq    %rax, %rsi
    movl    $.LC1, %edi
    movl    $0, %eax
    call    __isoc99_scanf
    jmp    .L2
.L5:
    .loc 1 8 0
    nop
.L2:
    .loc 1 8 0 is_stmt 0 discriminator 1
    movl    -4(%rbp), %eax
    testl    %eax, %eax
    jne    .L5

This looks fine to me.
Which might mean this is an interesting issue with debugging info.

[Bug debug/52160] gdb ignores line "bar: if(foo)goto bar;"

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52160

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jan.kratochvil at redhat
                   |                            |dot com

--- Comment #2 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2012-09-16 07:09:26 UTC ---
The same problem with IMO more minimal reproducer:
------------------------------------------------------------------------------
int i;
void f (void)
{
 redo:
  if (i)
    goto redo;
}
int main (void)
{
  f ();
  return 0;
}
------------------------------------------------------------------------------
(gdb) break f
Breakpoint 1 at 0x4004c2: file 123.c, line 6.
(gdb) run
Starting program: /home/jkratoch/t/123 
[Inferior 1 (process 308) exited normally]
------------------------------------------------------------------------------
f:
.LFB0:
        .file 1 "123.c"
        .loc 1 3 0
        .cfi_startproc
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        jmp     .L2
.L4:
        .loc 1 6 0
<-- GDB places breakpoint here
        nop
.L2:
        .loc 1 5 0

[Bug debug/52160] gdb ignores line "bar: if(foo)goto bar;"

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52160

--- Comment #3 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2012-09-16 07:10:39 UTC ---
FAIL: gcc (GCC) 4.4.7
FAIL: gcc (GCC) 4.5.4
FAIL: gcc (GCC) 4.6.4 20120916 (prerelease)
FAIL: gcc (GCC) 4.7.2 20120916 (prerelease)
FAIL: gcc (GCC) 4.8.0 20120916 (experimental)

[Bug debug/52160] gdb ignores line "bar: if(foo)goto bar;"

[palves at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52160

Pedro Alves <palves at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |palves at redhat dot com

--- Comment #4 from Pedro Alves <palves at redhat dot com> 2013-04-12 18:59:23 UTC ---
GDB PR15360 at <http://sourceware.org/bugzilla/show_bug.cgi?id=15360>
shows another reproducer:

 (gdb) b function
 Breakpoint 1 at 0x400569: file pr15360.c, line 9.
 (gdb) r
 ...
 ...exited normally.

GDB wants to put the breakpoint after the prologue of 'function', but:

(gdb) disassemble /m function
Dump of assembler code for function function():
8       {
   0x000000000040055c <+0>:     push   %rbp
   0x000000000040055d <+1>:     mov    %rsp,%rbp
   0x0000000000400560 <+4>:     push   %r12
   0x0000000000400562 <+6>:     push   %rbx
   0x0000000000400563 <+7>:     sub    $0x10,%rsp
   0x0000000000400567 <+11>:    jmp    0x40056a <function()+14>

9         do{
   0x0000000000400569 <+13>:    nop

10          int i = 0;
   0x000000000040056a <+14>:    movl   $0x0,-0x14(%rbp)

...
  Extended opcode 2: set Address to 0x40055c
  Special opcode 12: advance Address by 0 to 0x40055c and Line by 7 to 8
  Special opcode 188: advance Address by 13 to 0x400569 and Line by 1 to 9
...

Why is the jmp in the prologue's line?  That's what causes the issue.  GDB has
long (since ever?) skipped the line where the prologue is to find the first
instruction of "user code".

[Bug debug/52160] gdb ignores line "bar: if(foo)goto bar;"

[ssbssa at yahoo dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52160

Hannes Domani <ssbssa at yahoo dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ssbssa at yahoo dot de

--- Comment #5 from Hannes Domani <ssbssa at yahoo dot de> ---
I can reproduce this issue with gcc-4.6.1, but not with gcc-4.9.1 or newer, so
I think this has been fixed already.