xref: /titanic_51/usr/src/lib/libc/amd64/sys/vforkx.s (revision 2917a9c9c3eee6fcaedb239f5f68da01f4ed0da9)
1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22/*
23 * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
24 * Use is subject to license terms.
25 */
26
27#pragma ident	"%Z%%M%	%I%	%E% SMI"
28
29	.file	"%M%"
30
31#include <sys/asm_linkage.h>
32
33	ANSI_PRAGMA_WEAK(vforkx,function)
34	ANSI_PRAGMA_WEAK(vfork,function)
35
36#include "SYS.h"
37#include <assym.h>
38
39/*
40 * pid = vforkx(flags);
41 * syscall trap: forksys(2, flags)
42 *
43 * pid = vfork();
44 * syscall trap: forksys(2, 0)
45 *
46 * From the syscall:
47 * %edx == 0 in parent process, %edx = 1 in child process.
48 * %eax == pid of child in parent, %eax == pid of parent in child.
49 *
50 * The child gets a zero return value.
51 * The parent gets the pid of the child.
52 */
53
54/*
55 * The child of vfork() will execute in the parent's address space,
56 * thereby changing the stack before the parent runs again.
57 * Therefore we have to be careful how we return from vfork().
58 * Pity the poor debugger developer who has to deal with this kludge.
59 *
60 * We block all blockable signals while performing the vfork() system call
61 * trap.  This enables us to set curthread->ul_vfork safely, so that we
62 * don't end up in a signal handler with curthread->ul_vfork set wrong.
63 */
64
65	ENTRY_NP(vforkx)
66	movq	%rdi, %r8		/* flags */
67	jmp	0f
68	ENTRY_NP(vfork)
69	xorq	%r8, %r8		/* flags = 0 */
700:
71	popq	%r9			/* save return %rip in %r9 */
72	movl	$MASKSET1, %edx		/* block all signals */
73	movl	$MASKSET0, %esi
74	movl	$SIG_SETMASK, %edi
75	__SYSCALL(lwp_sigmask)
76
77	movq	%r8, %rsi		/* flags */
78	movl	$2, %edi
79	__SYSCALL(forksys)		/* vforkx(flags) */
80	jae 	1f
81
82	/* reconstruct stack before jumping to __cerror */
83	pushq	%r9
84	movq	%rax, %r8		/* save the vfork() error number */
85
86	movl	%fs:UL_SIGMASK+4, %edx	/* reinstate signals */
87	movl	%fs:UL_SIGMASK, %esi
88	movl	$SIG_SETMASK, %edi
89	__SYSCALL(lwp_sigmask)
90
91	movq	%r8, %rax		/* restore the vfork() error number */
92	jmp	__cerror
93
941:
95	/*
96	 * To determine if we are (still) a child of vfork(), the child
97	 * increments curthread->ul_vfork by one and the parent decrements
98	 * it by one.  If the result is zero, then we are not a child of
99	 * vfork(), else we are.  We do this to deal with the case of
100	 * a vfork() child calling vfork().
101	 */
102	cmpl	$0, %edx
103	jne	2f
104	movl	%fs:UL_VFORK, %edx
105	cmpl	$0, %edx		/* don't let it go negative */
106	je	3f
107	subl	$1, %edx		/* curthread->ul_vfork--; */
108	jmp	3f
1092:
110	xorl	%eax, %eax		/* zero the return value in the child */
111	movl	%fs:UL_VFORK, %edx
112	addl	$1, %edx		/* curthread->ul_vfork++; */
1133:
114	movl	%edx, %fs:UL_VFORK
115	/*
116	 * Clear the schedctl interface in both parent and child.
117	 * (The child might have modified the parent.)
118	 */
119	xorq	%rdx, %rdx
120	movq	%rdx, %fs:UL_SCHEDCTL
121	movq	%rdx, %fs:UL_SCHEDCTL_CALLED
122	movq	%rax, %r8		/* save the vfork() return value */
123
124	movl	%fs:UL_SIGMASK+4, %edx	/* reinstate signals */
125	movl	%fs:UL_SIGMASK, %esi
126	movl	$SIG_SETMASK, %edi
127	__SYSCALL(lwp_sigmask)
128
129	movq	%r8, %rax		/* restore the vfork() return value */
130	jmp	*%r9			/* jump back to the caller */
131	SET_SIZE(vfork)
132	SET_SIZE(vforkx)
133