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, Version 1.0 only
6 * (the "License"). You may not use this file except in compliance
7 * with the License.
8 *
9 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
10 * or http://www.opensolaris.org/os/licensing.
11 * See the License for the specific language governing permissions
12 * and limitations under the License.
13 *
14 * When distributing Covered Code, include this CDDL HEADER in each
15 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
16 * If applicable, add the following below this CDDL HEADER, with the
17 * fields enclosed by brackets "[]" replaced with your own identifying
18 * information: Portions Copyright [yyyy] [name of copyright owner]
19 *
20 * CDDL HEADER END
21 */
22 /*
23 * Copyright 2004 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 /*
30 * Debugger co-routine context support: In order to implement the context-
31 * switching necessary for MDB pipes, we need the ability to establish a
32 * co-routine context that has a separate stack. We use this stack to execute
33 * the MDB parser, and then switch back and forth between this code and the
34 * dcmd which is producing output to be consumed. We implement a context by
35 * mapping a few pages of anonymous memory, and then using setcontext(2) to
36 * switch to this stack and begin execution of a new function.
37 */
38
39 #include <mdb/mdb_context_impl.h>
40 #include <mdb/mdb_modapi.h>
41 #include <mdb/mdb_debug.h>
42 #include <mdb/mdb_err.h>
43
44 #include <sys/types.h>
45 #include <sys/mman.h>
46
47 #include <ucontext.h>
48 #include <unistd.h>
49 #include <setjmp.h>
50 #include <fcntl.h>
51 #include <errno.h>
52
53 static void
context_init(mdb_context_t * volatile c)54 context_init(mdb_context_t *volatile c)
55 {
56 c->ctx_status = c->ctx_func();
57 ASSERT(c->ctx_resumes > 0);
58 longjmp(c->ctx_pcb, 1);
59 }
60
61 mdb_context_t *
mdb_context_create(int (* func)(void))62 mdb_context_create(int (*func)(void))
63 {
64 mdb_context_t *c = mdb_zalloc(sizeof (mdb_context_t), UM_NOSLEEP);
65 size_t pagesize = sysconf(_SC_PAGESIZE);
66 int prot = sysconf(_SC_STACK_PROT);
67 static int zfd = -1;
68
69 if (c == NULL)
70 return (NULL);
71
72 if (prot == -1)
73 prot = PROT_READ | PROT_WRITE | PROT_EXEC;
74
75 c->ctx_func = func;
76 c->ctx_stacksize = pagesize * 4;
77 c->ctx_stack = mmap(NULL, c->ctx_stacksize, prot,
78 MAP_PRIVATE | MAP_ANON, -1, 0);
79
80 /*
81 * If the mmap failed with EBADFD, this kernel doesn't have MAP_ANON
82 * support; fall back to opening /dev/zero, caching the fd, and using
83 * that to mmap chunks of anonymous memory.
84 */
85 if (c->ctx_stack == MAP_FAILED && errno == EBADF) {
86 if (zfd == -1 && (zfd = open("/dev/zero", O_RDWR)) >= 0)
87 (void) fcntl(zfd, F_SETFD, FD_CLOEXEC);
88
89 if (zfd >= 0) {
90 c->ctx_stack = mmap(NULL, c->ctx_stacksize, prot,
91 MAP_PRIVATE, zfd, 0);
92 }
93 }
94
95 c->ctx_uc.uc_flags = UC_ALL;
96 if (c->ctx_stack == MAP_FAILED || getcontext(&c->ctx_uc) != 0) {
97 mdb_free(c, sizeof (mdb_context_t));
98 return (NULL);
99 }
100
101 c->ctx_uc.uc_stack.ss_sp = c->ctx_stack;
102 c->ctx_uc.uc_stack.ss_size = c->ctx_stacksize;
103 c->ctx_uc.uc_stack.ss_flags = 0;
104 c->ctx_uc.uc_link = NULL;
105 makecontext(&c->ctx_uc, context_init, 1, c);
106
107 return (c);
108 }
109
110 void
mdb_context_destroy(mdb_context_t * c)111 mdb_context_destroy(mdb_context_t *c)
112 {
113 if (munmap(c->ctx_stack, c->ctx_stacksize) == -1)
114 fail("failed to unmap stack %p", c->ctx_stack);
115
116 mdb_free(c, sizeof (mdb_context_t));
117 }
118
119 void
mdb_context_switch(mdb_context_t * c)120 mdb_context_switch(mdb_context_t *c)
121 {
122 if (setjmp(c->ctx_pcb) == 0 && setcontext(&c->ctx_uc) == -1)
123 fail("failed to change context to %p", (void *)c);
124 else
125 fail("unexpectedly returned from context %p", (void *)c);
126 }
127
128 jmp_buf *
mdb_context_getpcb(mdb_context_t * c)129 mdb_context_getpcb(mdb_context_t *c)
130 {
131 c->ctx_resumes++;
132 return (&c->ctx_pcb);
133 }
134