Print this page
patch feedback
6507 i386 makecontext(3c) needs to 16-byte align the stack
Split |
Close |
Expand all |
Collapse all |
--- old/usr/src/lib/libc/i386/gen/makectxt.c
+++ new/usr/src/lib/libc/i386/gen/makectxt.c
1 1 /*
2 2 * CDDL HEADER START
3 3 *
4 4 * The contents of this file are subject to the terms of the
5 5 * Common Development and Distribution License (the "License").
6 6 * You may not use this file except in compliance with the License.
7 7 *
8 8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 9 * or http://www.opensolaris.org/os/licensing.
10 10 * See the License for the specific language governing permissions
11 11 * and limitations under the License.
12 12 *
13 13 * When distributing Covered Code, include this CDDL HEADER in each
14 14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 15 * If applicable, add the following below this CDDL HEADER, with the
16 16 * fields enclosed by brackets "[]" replaced with your own identifying
17 17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 18 *
19 19 * CDDL HEADER END
↓ open down ↓ |
19 lines elided |
↑ open up ↑ |
20 20 */
21 21
22 22 /*
23 23 * Copyright 2008 Sun Microsystems, Inc. All rights reserved.
24 24 * Use is subject to license terms.
25 25 */
26 26
27 27 /* Copyright (c) 1988 AT&T */
28 28 /* All Rights Reserved */
29 29
30 -#pragma ident "%Z%%M% %I% %E% SMI"
31 -
32 30 #pragma weak _makecontext = makecontext
33 31
34 32 #include "lint.h"
35 33 #include <stdarg.h>
36 34 #include <ucontext.h>
37 35 #include <sys/stack.h>
38 36
39 37 /*
40 38 * The ucontext_t that the user passes in must have been primed with a
41 39 * call to getcontext(2), have the uc_stack member set to reflect the
42 40 * stack which this context will use, and have the uc_link member set
43 41 * to the context which should be resumed when this context returns.
44 42 * When makecontext() returns, the ucontext_t will be set to run the
45 43 * given function with the given parameters on the stack specified by
46 44 * uc_stack, and which will return to the ucontext_t specified by uc_link.
47 45 */
48 46
47 +/*
48 + * The original i386 ABI said that the stack pointer need be only 4-byte
49 + * aligned before a function call (STACK_ALIGN == 4). The ABI supplement
50 + * version 1.0 changed the required alignment to 16-byte for the benefit of
51 + * floating point code compiled using sse2. The compiler assumes this
52 + * alignment and maintains it for calls it generates. If the stack is
53 + * initially properly aligned, it will continue to be so aligned. If it is
54 + * not initially so aligned, it will never become so aligned.
55 + *
56 + * One slightly confusing detail to keep in mind is that the 16-byte
57 + * alignment (%esp & 0xf == 0) is true just *before* the call instruction.
58 + * The call instruction will then push a return value, decrementing %esp by
59 + * 4. Therefore, if one dumps %esp at the at the very first instruction in
60 + * a function, it will end with a 0xc. The compiler expects this and
61 + * compensates for it properly.
62 + *
63 + * Note: If you change this value, you need to change it in the following
64 + * files as well:
65 + *
66 + * - lib/libc/i386/threads/machdep.c
67 + * - lib/common/i386/crti.s
68 + * - lib/common/i386/crt1.s
69 + */
70 +#undef STACK_ALIGN
71 +#define STACK_ALIGN 16
72 +
49 73 static void resumecontext(void);
50 74
51 75 void
52 76 makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
53 77 {
54 78 long *sp;
55 79 long *tsp;
56 80 va_list ap;
57 81 size_t size;
58 82
59 83 ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
60 84
61 85 size = sizeof (long) * (argc + 1);
62 86
63 - sp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
87 + tsp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
64 88 ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
65 89
66 - tsp = sp + 1;
67 -
68 - va_start(ap, argc);
69 -
70 - while (argc-- > 0) {
71 - *tsp++ = va_arg(ap, long);
72 - }
73 -
74 - va_end(ap);
90 + /*
91 + * Since we're emulating the call instruction, we must push the
92 + * return address (which involves adjusting the stack pointer to
93 + * have the proper 4-byte bias).
94 + */
95 + sp = tsp - 1;
75 96
76 97 *sp = (long)resumecontext; /* return address */
77 98
78 99 ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
100 +
101 + /*
102 + * "push" all the arguments
103 + */
104 + va_start(ap, argc);
105 + while (argc-- > 0)
106 + *tsp++ = va_arg(ap, long);
107 + va_end(ap);
79 108 }
80 109
81 110
82 111 static void
83 112 resumecontext(void)
84 113 {
85 114 ucontext_t uc;
86 115
87 116 (void) getcontext(&uc);
88 117 (void) setcontext(uc.uc_link);
89 118 }
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX