Re: GDB infinite loop when stepping on "while (1) i++;"

[Kunal Parmar <kunal.parmar@celunite.com>]

Hi,

On Thu, 2007-03-22 at 15:44 +0800, qinwei wrote:
> Dears, problems are here:
> 
> gcc -o t -gdwarf-2 tp_while1.c
> gdb t
> (gdb) b main
> Breakpoint 1 at 0x8048350: file tp_while1.c, line 3.
> (gdb) r
> Starting program: /home/qinwei/GJ283/code/build_linux/debug-gdb/t 
> 
> Breakpoint 1, main () at tp_while1.c:3
> 3         int i = 10;
> (gdb) n
> 4         while (1) i++;
> (gdb) n
> 
> When program stops at "while (1) i++;", and printing "next" command will 
> cause gdb infinite loop. 
> The target are x86, score, or other? (gdb-6.6 release version)
> 
> Is the reason that the following dwarf-2 info:
> 
>   "Special opcode 104: advance Address by 7 to 0x8048357 and Line by 1 to 
> 4"
>   "Advance PC by 7 to 804835e"
> 
> which makes "while (1)" and "i++;" the same line number? And gdb will get
> "stop_pc" from the range [0x8048357, 0x804835e] and will not stop?

Yes. The command `next' is used to move to advance execution to the next
line of the current function. 

> How to solve it?  Thanks!

Try using `nexti' of `stepi'.

Cheers,
Kunal

> 
> int main (void)
> {
>   int i = 10; 
>   while (1) i++;
>   return 0;
> }
> 
>  Line Number Statements:
>   Extended opcode 2: set Address to 0x8048334
>   Special opcode 6: advance Address by 0 to 0x8048334 and Line by 1 to 2
>   Advance PC by constant 17 to 0x8048345
>   Special opcode 160: advance Address by 11 to 0x8048350 and Line by 1 to 
> 3
>   Special opcode 104: advance Address by 7 to 0x8048357 and Line by 1 to 4
>   Advance PC by 7 to 804835e 
>   Extended opcode 1: End of Sequence
> 
> 08048334 <main>:
>  8048334:   55                      push   %ebp
>  8048335:   89 e5                   mov    %esp,%ebp
>  8048337:   83 ec 08                sub    $0x8,%esp
>  804833a:   83 e4 f0                and    $0xfffffff0,%esp
>  804833d:   b8 00 00 00 00          mov    $0x0,%eax
>  8048342:   83 c0 0f                add    $0xf,%eax
>  8048345:   83 c0 0f                add    $0xf,%eax
>  8048348:   c1 e8 04                shr    $0x4,%eax
>  804834b:   c1 e0 04                shl    $0x4,%eax
>  804834e:   29 c4                   sub    %eax,%esp
>  8048350:   c7 45 fc 0a 00 00 00    movl   $0xa,0xfffffffc(%ebp)
>  8048357:   8d 45 fc                lea    0xfffffffc(%ebp),%eax
>  804835a:   ff 00                   incl   (%eax)
>  804835c:   eb f9                   jmp    8048357 <main+0x23>
>  804835e:   90                      nop
>  804835f:   90                      nop
> 
> Best regards,
> Qinwei
> Mail  qinwei@sunnorth.com.cn
> Phone +86-010-62981668-2708
> Fax   +86-010-62985972
-- 
Kunal Parmar
Tools Team,
Celunite Inc. (www.celunite.com)