Using sysarch specific syscalls in assembly?

[John Baldwin]

On Tuesday 09 August 2005 09:31 am, alexander wrote:
> On Tue Aug  9 05, Robert Watson wrote:
> > In general, it is much preferable that applications link against libc to
> > get the system call stubs than that they directly invoke system calls.
> > That way, if compatibility interfaces are introduced, etc, the
> > application will continue to function.  For example, there was at one
> > point a migration away from explicit system calls to set certain kernel
> > parameters, such as hostname and domainname, towards using sysctl, with
> > the system calls being marked obsolete.  The C library still provides a
> > sethostname() interface, which is actually a wrapper in user space around
> > sysctl().  So invoking the C function provided by libc for a system call
> > will generally be preferred, even if the originating code is assembly.
> >
> > Robert N M Watson
>
> Thx. I'll try that.
>
> 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
> 	lea esp,[esp+8]
> 	ret

Just change this to:

	push byte ioperm_args		; this might be wrong, you need
					; to be pushing a 32-bit pointer
					; to the ioperm_args structure, not
					; a byte
	push dword I386_SET_IOPERM
	call sysarch
	addl $8,%esp
	ret

To use the sysarch() function in libc.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org