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
53static void
54context_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
61mdb_context_t *
62mdb_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
110void
111mdb_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
119void
120mdb_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
128jmp_buf *
129mdb_context_getpcb(mdb_context_t *c)
130{
131	c->ctx_resumes++;
132	return (&c->ctx_pcb);
133}
134