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/param.h> 30 #include <sys/signal.h> 31 #include <sys/ucontext.h> 32 33 #include <errno.h> 34 #include <stdarg.h> 35 #include <stdlib.h> 36 #include <unistd.h> 37 38 /* Prototypes */ 39 extern void _ctx_start(ucontext_t *, int argc, ...); 40 41 42 __weak_reference(__makecontext, makecontext); 43 44 void 45 _ctx_done (ucontext_t *ucp) 46 { 47 if (ucp->uc_link == NULL) 48 exit(0); 49 else { 50 /* 51 * Since this context has finished, don't allow it 52 * to be restarted without being reinitialized (via 53 * setcontext or swapcontext). 54 */ 55 ucp->uc_mcontext.mc_len = 0; 56 57 /* Set context to next one in link */ 58 /* XXX - what to do for error, abort? */ 59 setcontext((const ucontext_t *)ucp->uc_link); 60 abort(); /* should never get here */ 61 } 62 } 63 64 void 65 __makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...) 66 { 67 va_list ap; 68 char *stack_top; 69 intptr_t *argp; 70 int i; 71 72 if (ucp == NULL) 73 return; 74 else if ((ucp->uc_stack.ss_sp == NULL) || 75 (ucp->uc_stack.ss_size < MINSIGSTKSZ)) { 76 /* 77 * This should really return -1 with errno set to ENOMEM 78 * or something, but the spec says that makecontext is 79 * a void function. At least make sure that the context 80 * isn't valid so it can't be used without an error. 81 */ 82 ucp->uc_mcontext.mc_len = 0; 83 } 84 /* XXX - Do we want to sanity check argc? */ 85 else if (argc < 0) { 86 ucp->uc_mcontext.mc_len = 0; 87 } 88 /* Make sure the context is valid. */ 89 else if (ucp->uc_mcontext.mc_len == sizeof(mcontext_t)) { 90 /* 91 * Arrange the stack as follows: 92 * 93 * _ctx_start() - context start wrapper 94 * start() - user start routine 95 * arg1 - first argument, aligned(16) 96 * ... 97 * argn 98 * ucp - this context, %ebp points here 99 * 100 * When the context is started, control will return to 101 * the context start wrapper which will pop the user 102 * start routine from the top of the stack. After that, 103 * the top of the stack will be setup with all arguments 104 * necessary for calling the start routine. When the 105 * start routine returns, the context wrapper then sets 106 * the stack pointer to %ebp which was setup to point to 107 * the base of the stack (and where ucp is stored). It 108 * will then call _ctx_done() to swap in the next context 109 * (uc_link != 0) or exit the program (uc_link == 0). 110 */ 111 stack_top = (char *)(ucp->uc_stack.ss_sp + 112 ucp->uc_stack.ss_size - sizeof(intptr_t)); 113 114 /* 115 * Adjust top of stack to allow for 3 pointers (return 116 * address, _ctx_start, and ucp) and argc arguments. 117 * We allow the arguments to be pointers also. The first 118 * argument to the user function must be properly aligned. 119 */ 120 stack_top = stack_top - (sizeof(intptr_t) * (1 + argc)); 121 stack_top = (char *)((unsigned)stack_top & ~15); 122 stack_top = stack_top - (2 * sizeof(intptr_t)); 123 argp = (intptr_t *)stack_top; 124 125 /* 126 * Setup the top of the stack with the user start routine 127 * followed by all of its aguments and the pointer to the 128 * ucontext. We need to leave a spare spot at the top of 129 * the stack because setcontext will move eip to the top 130 * of the stack before returning. 131 */ 132 *argp = (intptr_t)_ctx_start; /* overwritten with same value */ 133 argp++; 134 *argp = (intptr_t)start; 135 argp++; 136 137 /* Add all the arguments: */ 138 va_start(ap, argc); 139 for (i = 0; i < argc; i++) { 140 *argp = va_arg(ap, intptr_t); 141 argp++; 142 } 143 va_end(ap); 144 145 /* The ucontext is placed at the bottom of the stack. */ 146 *argp = (intptr_t)ucp; 147 148 /* 149 * Set the machine context to point to the top of the 150 * stack and the program counter to the context start 151 * wrapper. Note that setcontext() pushes the return 152 * address onto the top of the stack, so allow for this 153 * by adjusting the stack downward 1 slot. Also set 154 * %esi to point to the base of the stack where ucp 155 * is stored. 156 */ 157 ucp->uc_mcontext.mc_esi = (int)argp; 158 ucp->uc_mcontext.mc_ebp = 0; 159 ucp->uc_mcontext.mc_esp = (int)stack_top + sizeof(caddr_t); 160 ucp->uc_mcontext.mc_eip = (int)_ctx_start; 161 } 162 } 163