Using sysarch specific syscalls in assembly?

[ari edelkind]

On 8/9/2005, "alexander" <arundel at h3c.de> wrote:

[...]
>Unfortunately I'm experiencing some problems right now. From time to time
>I'm getting a
>
>'Bus error: 10 (core dumped)'
>
>This however appears randomly. One time I run the app everything works fine,the
>next time it core dumps. Are there any errors in my code?
>
>%define SYSARCH		165	; syscall sysarch(2)
>%define I386_SET_IOPERM 4	; i386_set_ioperm(2) number
>
>ioperm_args	dd	378h
>		dd	3
>		dd	1
>
>OpenIO:
>	push byte ioperm_args
>	push dword I386_SET_IOPERM
>	mov eax,SYSARCH
>	Call _syscall
[...]

You need to push a _pointer_ to a structure as your second argument to
sysarch(2).  This means something more along the lines of:

ioperm_args   dd  378h
              dd  3
              dd  1

argp          dd  ioperm_args

[...]
      push dword argp
      push dword I386_SET_IOPERM
[...]


Get this wrong, and you'll have unpredictable results.

ari