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__vfork14.S revision 1.9 
      1 /*	$NetBSD: __vfork14.S,v 1.9 2020/05/05 20:43:47 skrll Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2001 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Matt Fredette.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <sys/errno.h>
     33 #include "SYS.h"
     34 
     35 ENTRY(__vfork14, 0)
     36 	/*
     37 	 * NB: __vfork14 is a tricky syscall.  We can't save
     38 	 * any values on the stack, because the stack will be
     39 	 * trashed by the child, leaving garbage for when the
     40 	 * parent returns.
     41 	 *
     42 	 * So we must save values in registers, specifically,
     43 	 * registers that the kernel is willing to preserve
     44 	 * across the syscall.  Normally, this would be callee-
     45 	 * saved registers, with the kernel being the callee,
     46 	 * but the problem is that we, too, are a callee, and
     47 	 * would have to save that very same register somewhere,
     48 	 * because *our* caller is counting on us to do so.
     49 	 *
     50 	 * What we need is a normally caller-saved register,
     51 	 * that the kernel is willing to save for us.  The
     52 	 * syscall entry code in locore.S has been modified
     53 	 * to do just this for the t4 register.
     54 	 */
     55 	.import	__cerror, code
     56 
     57 	copy	%rp, %t4
     58 	ldil	L%SYSCALLGATE, %r1
     59 	ble	4(%sr2, %r1)
     60 	 ldi	SYS___vfork14, %t1
     61 	comb,=,n %r0, %t1, 1f
     62 	b	__cerror
     63 1:
     64 	 copy	%t4, %rp		// delay slot of branch to __cerror
     65 	addi	-1, %ret1, %ret1
     66 	bv	%r0(%rp)
     67 	 and	%ret0, %ret1, %ret0
     68 EXIT(__vfork14)
     69