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 __FBSDID("$FreeBSD$"); 31 32 #include <sys/param.h> 33 #include <sys/signal.h> 34 #include <sys/ucontext.h> 35 36 #include <errno.h> 37 #include <stdarg.h> 38 #include <stdlib.h> 39 #include <unistd.h> 40 41 /* Prototypes */ 42 extern void _ctx_start(ucontext_t *, int argc, ...); 43 44 45 __weak_reference(__makecontext, makecontext); 46 47 void 48 _ctx_done (ucontext_t *ucp) 49 { 50 if (ucp->uc_link == NULL) 51 exit(0); 52 else { 53 /* 54 * Since this context has finished, don't allow it 55 * to be restarted without being reinitialized (via 56 * setcontext or swapcontext). 57 */ 58 ucp->uc_mcontext.mc_len = 0; 59 60 /* Set context to next one in link */ 61 /* XXX - what to do for error, abort? */ 62 setcontext((const ucontext_t *)ucp->uc_link); 63 abort(); /* should never get here */ 64 } 65 } 66 67 void 68 __makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...) 69 { 70 va_list ap; 71 char *stack_top; 72 intptr_t *argp; 73 int i; 74 75 if (ucp == NULL) 76 return; 77 else if ((ucp->uc_stack.ss_sp == NULL) || 78 (ucp->uc_stack.ss_size < MINSIGSTKSZ)) { 79 /* 80 * This should really return -1 with errno set to ENOMEM 81 * or something, but the spec says that makecontext is 82 * a void function. At least make sure that the context 83 * isn't valid so it can't be used without an error. 84 */ 85 ucp->uc_mcontext.mc_len = 0; 86 } 87 /* XXX - Do we want to sanity check argc? */ 88 else if (argc < 0) { 89 ucp->uc_mcontext.mc_len = 0; 90 } 91 /* Make sure the context is valid. */ 92 else if (ucp->uc_mcontext.mc_len == sizeof(mcontext_t)) { 93 /* 94 * Arrange the stack as follows: 95 * 96 * _ctx_start() - context start wrapper 97 * start() - user start routine 98 * arg1 - first argument, aligned(16) 99 * ... 100 * argn 101 * ucp - this context, %ebp points here 102 * 103 * When the context is started, control will return to 104 * the context start wrapper which will pop the user 105 * start routine from the top of the stack. After that, 106 * the top of the stack will be setup with all arguments 107 * necessary for calling the start routine. When the 108 * start routine returns, the context wrapper then sets 109 * the stack pointer to %ebp which was setup to point to 110 * the base of the stack (and where ucp is stored). It 111 * will then call _ctx_done() to swap in the next context 112 * (uc_link != 0) or exit the program (uc_link == 0). 113 */ 114 stack_top = (char *)(ucp->uc_stack.ss_sp + 115 ucp->uc_stack.ss_size - sizeof(intptr_t)); 116 117 /* 118 * Adjust top of stack to allow for 3 pointers (return 119 * address, _ctx_start, and ucp) and argc arguments. 120 * We allow the arguments to be pointers also. The first 121 * argument to the user function must be properly aligned. 122 */ 123 stack_top = stack_top - (sizeof(intptr_t) * (1 + argc)); 124 stack_top = (char *)((unsigned)stack_top & ~15); 125 stack_top = stack_top - (2 * sizeof(intptr_t)); 126 argp = (intptr_t *)stack_top; 127 128 /* 129 * Setup the top of the stack with the user start routine 130 * followed by all of its aguments and the pointer to the 131 * ucontext. We need to leave a spare spot at the top of 132 * the stack because setcontext will move eip to the top 133 * of the stack before returning. 134 */ 135 *argp = (intptr_t)_ctx_start; /* overwritten with same value */ 136 argp++; 137 *argp = (intptr_t)start; 138 argp++; 139 140 /* Add all the arguments: */ 141 va_start(ap, argc); 142 for (i = 0; i < argc; i++) { 143 *argp = va_arg(ap, intptr_t); 144 argp++; 145 } 146 va_end(ap); 147 148 /* The ucontext is placed at the bottom of the stack. */ 149 *argp = (intptr_t)ucp; 150 151 /* 152 * Set the machine context to point to the top of the 153 * stack and the program counter to the context start 154 * wrapper. Note that setcontext() pushes the return 155 * address onto the top of the stack, so allow for this 156 * by adjusting the stack downward 1 slot. Also set 157 * %esi to point to the base of the stack where ucp 158 * is stored. 159 */ 160 ucp->uc_mcontext.mc_esi = (int)argp; 161 ucp->uc_mcontext.mc_ebp = 0; 162 ucp->uc_mcontext.mc_esp = (int)stack_top + sizeof(caddr_t); 163 ucp->uc_mcontext.mc_eip = (int)_ctx_start; 164 } 165 } 166