1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2001 Daniel M. Eischen <deischen@freebsd.org> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Neither the name of the author nor the names of its contributors 13 * may be used to endorse or promote products derived from this software 14 * without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #include <sys/cdefs.h> 30 #include <sys/param.h> 31 #include <sys/signal.h> 32 #include <sys/ucontext.h> 33 34 #include <errno.h> 35 #include <stdarg.h> 36 #include <stdlib.h> 37 #include <unistd.h> 38 39 /* Prototypes */ 40 extern void _ctx_start(ucontext_t *, int argc, ...); 41 42 43 __weak_reference(__makecontext, makecontext); 44 45 void 46 _ctx_done (ucontext_t *ucp) 47 { 48 if (ucp->uc_link == NULL) 49 exit(0); 50 else { 51 /* 52 * Since this context has finished, don't allow it 53 * to be restarted without being reinitialized (via 54 * setcontext or swapcontext). 55 */ 56 ucp->uc_mcontext.mc_len = 0; 57 58 /* Set context to next one in link */ 59 /* XXX - what to do for error, abort? */ 60 setcontext((const ucontext_t *)ucp->uc_link); 61 abort(); /* should never get here */ 62 } 63 } 64 65 void 66 __makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...) 67 { 68 va_list ap; 69 char *stack_top; 70 intptr_t *argp; 71 int i; 72 73 if (ucp == NULL) 74 return; 75 else if ((ucp->uc_stack.ss_sp == NULL) || 76 (ucp->uc_stack.ss_size < MINSIGSTKSZ)) { 77 /* 78 * This should really return -1 with errno set to ENOMEM 79 * or something, but the spec says that makecontext is 80 * a void function. At least make sure that the context 81 * isn't valid so it can't be used without an error. 82 */ 83 ucp->uc_mcontext.mc_len = 0; 84 } 85 /* XXX - Do we want to sanity check argc? */ 86 else if (argc < 0) { 87 ucp->uc_mcontext.mc_len = 0; 88 } 89 /* Make sure the context is valid. */ 90 else if (ucp->uc_mcontext.mc_len == sizeof(mcontext_t)) { 91 /* 92 * Arrange the stack as follows: 93 * 94 * _ctx_start() - context start wrapper 95 * start() - user start routine 96 * arg1 - first argument, aligned(16) 97 * ... 98 * argn 99 * ucp - this context, %ebp points here 100 * 101 * When the context is started, control will return to 102 * the context start wrapper which will pop the user 103 * start routine from the top of the stack. After that, 104 * the top of the stack will be setup with all arguments 105 * necessary for calling the start routine. When the 106 * start routine returns, the context wrapper then sets 107 * the stack pointer to %ebp which was setup to point to 108 * the base of the stack (and where ucp is stored). It 109 * will then call _ctx_done() to swap in the next context 110 * (uc_link != 0) or exit the program (uc_link == 0). 111 */ 112 stack_top = (char *)(ucp->uc_stack.ss_sp + 113 ucp->uc_stack.ss_size - sizeof(intptr_t)); 114 115 /* 116 * Adjust top of stack to allow for 3 pointers (return 117 * address, _ctx_start, and ucp) and argc arguments. 118 * We allow the arguments to be pointers also. The first 119 * argument to the user function must be properly aligned. 120 */ 121 stack_top = stack_top - (sizeof(intptr_t) * (1 + argc)); 122 stack_top = (char *)((unsigned)stack_top & ~15); 123 stack_top = stack_top - (2 * sizeof(intptr_t)); 124 argp = (intptr_t *)stack_top; 125 126 /* 127 * Setup the top of the stack with the user start routine 128 * followed by all of its aguments and the pointer to the 129 * ucontext. We need to leave a spare spot at the top of 130 * the stack because setcontext will move eip to the top 131 * of the stack before returning. 132 */ 133 *argp = (intptr_t)_ctx_start; /* overwritten with same value */ 134 argp++; 135 *argp = (intptr_t)start; 136 argp++; 137 138 /* Add all the arguments: */ 139 va_start(ap, argc); 140 for (i = 0; i < argc; i++) { 141 *argp = va_arg(ap, intptr_t); 142 argp++; 143 } 144 va_end(ap); 145 146 /* The ucontext is placed at the bottom of the stack. */ 147 *argp = (intptr_t)ucp; 148 149 /* 150 * Set the machine context to point to the top of the 151 * stack and the program counter to the context start 152 * wrapper. Note that setcontext() pushes the return 153 * address onto the top of the stack, so allow for this 154 * by adjusting the stack downward 1 slot. Also set 155 * %esi to point to the base of the stack where ucp 156 * is stored. 157 */ 158 ucp->uc_mcontext.mc_esi = (int)argp; 159 ucp->uc_mcontext.mc_ebp = 0; 160 ucp->uc_mcontext.mc_esp = (int)stack_top + sizeof(caddr_t); 161 ucp->uc_mcontext.mc_eip = (int)_ctx_start; 162 } 163 } 164