Re: Need help in understanding x86 syscall

[linux-os (Dick Johnson)]

On Thu, 11 Aug 2005, Steven Rostedt wrote:

> On Thu, 2005-08-11 at 13:10 -0400, linux-os (Dick Johnson) wrote:
>> On Thu, 11 Aug 2005, Coywolf Qi Hunt wrote:
>
>>>>
>>>
>>> Also glibc support.
>>>
>>> --
>>> Coywolf Qi Hunt
>>> http://ahbl.org/~coywolf/
>>
>> Probably doesn't use int 0x80 at all.
>
> $ objdump -Dhalpr /lib/libc.so.6 | egrep 'int *\$0x80' | wc
>   448    2240   20160
>
> And a little snapshot:
>
> 000288d0 <__libc_sigsuspend>:
>   288d0:       55                      push   %ebp
>   288d1:       89 e5                   mov    %esp,%ebp
>   288d3:       57                      push   %edi
>   288d4:       56                      push   %esi
>   288d5:       53                      push   %ebx
>   288d6:       e8 00 00 00 00          call   288db <__libc_sigsuspend+0xb>
>   288db:       5b                      pop    %ebx
>   288dc:       81 c3 19 c7 0e 00       add    $0xec719,%ebx
>   288e2:       8b 83 b4 32 00 00       mov    0x32b4(%ebx),%eax
>   288e8:       85 c0                   test   %eax,%eax
>   288ea:       75 23                   jne    2890f <__libc_sigsuspend+0x3f>
>   288ec:       b9 08 00 00 00          mov    $0x8,%ecx
>   288f1:       8b 55 08                mov    0x8(%ebp),%edx
>   288f4:       87 d3                   xchg   %edx,%ebx
>   288f6:       b8 b3 00 00 00          mov    $0xb3,%eax
>   288fb:       cd 80                   int    $0x80
>   288fd:       87 d3                   xchg   %edx,%ebx
>   288ff:       89 c6                   mov    %eax,%esi
>   28901:       3d 00 f0 ff ff          cmp    $0xfffff000,%eax
>   28906:       77 33                   ja     2893b <__libc_sigsuspend+0x6b>
>   28908:       89 f0                   mov    %esi,%eax
>   2890a:       5b                      pop    %ebx
>   2890b:       5e                      pop    %esi
>   2890c:       5f                      pop    %edi
>   2890d:       5d                      pop    %ebp
>   2890e:       c3                      ret
>
> 288fb seems to use "int 0x80"  and so do all the other system calls that
> I inspected.
>
> $ ls -l /lib/libc.so.6
> lrwxrwxrwx  1 root root 13 2005-08-09 22:28 /lib/libc.so.6 -> libc-2.3.5.so
>
>
> -- Steve
>

I was talking about the one who had the glibc support to use
the newer system-call entry (who's name can confuse).

You are looking at code that uses int 0x80. It's an interrupt,
therefore, in the kernel, once the stack is set up, interrupts
need to be (re)enabled.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.12 on an i686 machine (5537.79 BogoMips).
Warning : 98.36% of all statistics are fiction.
.
I apologize for the following. I tried to kill it with the above dot :

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