[OpenWrt-Devel] vfork segfault in openwrt

[Qi Li]

Hi,
I am using armv7 for openwrt development and facing a segfault caused by vfork.
I have wrote a small test program with the following segments:
        ...
        pid_t child_t;
        if((child_t = vfork()) < 0)
        {
            printf("error!\n");
            return -1;
        }
        else if(child_t == 0)
        {
            printf("in child:pid =%d\n",getpid());
            sleep(2);
            _exit(0);
        }
        else
        {
            printf("in parent:child_t id = %d,pid = %d\n",child_t,getpid());
        }
       ...
The vfork() function always cause segfault, this is the gdb debug trace:
...
   (gdb) c
       Breakpoint 1, main (argc=1, argv=0xbefffed4) at handler.c:33
       33            if((child_t = vfork()) < 0)
   (gdb) stepi
       0x00008474 in vfork () at libpthread/nptl/sysdeps/unix/sysv/linux/arm/../../../../../../../libc/sysdeps/linux/arm/vfork.S:71
       71        SAVE_PID
   (gdb) l
       66
       67    #else
       68    __vfork:
       69
       70    #ifdef __NR_vfork
       71        SAVE_PID
       72        DO_CALL (vfork)
       73        RESTORE_PID
       74        cmn    r0, #4096
       75        IT(t, cc)
  (gdb) b libpthread/nptl/sysdeps/unix/sysv/linux/arm/../../../../../../../libc/sysdeps/linux/arm/vfork.S:72
       Breakpoint 2 at 0xb6fcf930: file libpthread/nptl/sysdeps/unix/sysv/linux/arm/../../../../../../../libc/sysdeps/linux/arm/vfork.S, line 72.
  (gdb) disassemble
           0x00008584 <+40>:        bl      0x8444 <puts>
     => 0x00008588 <+44>:         bl      0x8474 <vfork>
           0x0000858c <+48>:         str    r0, [r11, #-12]
  (gdb)stepi
     ...
  (gdb) stepi
       0x00008474 in vfork () at libpthread/nptl/sysdeps/unix/sysv/linux/arm/../../../../../../../libc/sysdeps/linux/arm/vfork.S:71
       71              SAVE_PID
  (gdb) disassemble
       Dump of assembler code for function vfork:
       =>  0x00008474 <+0>:   add  r12, pc, #0, 12
              0x00008478 <+4>:   add  r12, r12, #8, 20        ; 0x8000
              0x0000847c <+8>:   ldr    pc, [r12, #796]!        ; 0x31c
  (gdb) stepi
      ...
   (gdb) disassemble
        Dump of assembler code for function vfork:
             0x00008474 <+0>:   add  r12, pc, #0, 12
             0x00008478 <+4>:   add  r12, r12, #8, 20        ; 0x8000
       => 0x0000847c <+8>:     ldr    pc, [r12, #796]!        ; 0x31c
   (gdb)c
       Continuing.
       Program received signal SIGSEGV, Segmentation fault.
       0xffff0fe0 in ?? ()
    (gdb)
I have also found the vfork code at vfork.S:
__vfork:

#ifdef __NR_vfork
    SAVE_PID
    DO_CALL (vfork)
    RESTORE_PID
    cmn    r0, #4096
    IT(t, cc)
#if defined(__USE_BX__)
    bxcc    lr
#else
    movcc    pc, lr
#endif

    /* Check if vfork even exists.  */
    ldr     r1, =-ENOSYS
    teq     r0, r1
    bne     __error
#endif

    /* If we don't have vfork, use fork.  */
    DO_CALL (fork)
    cmn     r0, #4096

    /* Syscall worked.  Return to child/parent */
    IT(t, cc)
#if defined(__USE_BX__)
    bxcc    lr
#else
    movcc   pc, lr
#endif

__error:
    b    __syscall_error
#endif


It just seems that SAVE_PID instruction cause some problem.
Could anyone help?

Thanks,
Qi
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