source: trunk/minix/lib/i86/misc/alloca.s@ 9

#
!       alloca() - allocate space on the stack          Author: Kees J. Bot
!                                                               26 Jan 1994

#if __ACK__     /* BCC can't do alloca(), register saving is wrong. */

.text
.define _alloca
_alloca:
        pop     cx              ! Return address
        pop     ax              ! Bytes to allocate
        add     ax, #2*2+1      ! Add space for two saved register variables
        andb    al, #0xFE       ! Align
        mov     bx, sp          ! Keep current sp
        sub     sp, ax          ! Lower stack
        mov     ax, sp          ! Return value
        push    2(bx)           ! Push what is probably the saved si
        push    (bx)            ! Saved di
                                ! Now ACK can still do:
                                !       pop di; pop si; mov sp, bp; pop bp; ret
        push    ax              ! Dummy argument
        jmp     (cx)
#endif