1 /* 2 * Copyright (c) 2001 Daniel M. Eischen <deischen@freebsd.org> 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Neither the name of the author nor the names of its contributors 11 * may be used to endorse or promote products derived from this software 12 * without specific prior written permission. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 */ 26 27 #include <sys/cdefs.h> 28 __FBSDID("$FreeBSD$"); 29 30 #include <sys/param.h> 31 #include <sys/signal.h> 32 33 #include <errno.h> 34 #include <stdarg.h> 35 #include <ucontext.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_flags = 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_flags = 0; 83 } 84 /* XXX - Do we want to sanity check argc? */ 85 else if ((argc < 0) || (argc > NCARGS)) { 86 ucp->uc_mcontext.mc_flags = 0; 87 } 88 /* Make sure the context is valid. */ 89 else if ((ucp->uc_mcontext.mc_flags & __UC_MC_VALID) != 0) { 90 /* 91 * Arrange the stack as follows: 92 * 93 * _ctx_start() - context start wrapper 94 * start() - user start routine 95 * arg1 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(double)); 113 stack_top = (char *)ALIGN(stack_top); 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. 119 */ 120 stack_top = stack_top - (sizeof(intptr_t) * (3 + argc)); 121 argp = (intptr_t *)stack_top; 122 123 /* 124 * Setup the top of the stack with the user start routine 125 * followed by all of its aguments and the pointer to the 126 * ucontext. We need to leave a spare spot at the top of 127 * the stack because setcontext will move eip to the top 128 * of the stack before returning. 129 */ 130 *argp = (intptr_t)_ctx_start; /* overwritten with same value */ 131 argp++; 132 *argp = (intptr_t)start; 133 argp++; 134 135 /* Add all the arguments: */ 136 va_start(ap, argc); 137 for (i = 0; i < argc; i++) { 138 *argp = va_arg(ap, intptr_t); 139 argp++; 140 } 141 va_end(ap); 142 143 /* The ucontext is placed at the bottom of the stack. */ 144 *argp = (intptr_t)ucp; 145 146 /* 147 * Set the machine context to point to the top of the 148 * stack and the program counter to the context start 149 * wrapper. Note that setcontext() pushes the return 150 * address onto the top of the stack, so allow for this 151 * by adjusting the stack downward 1 slot. Also set 152 * %ebp to point to the base of the stack where ucp 153 * is stored. 154 */ 155 ucp->uc_mcontext.mc_ebp = (int)argp; 156 ucp->uc_mcontext.mc_esp = (int)stack_top + sizeof(caddr_t); 157 ucp->uc_mcontext.mc_eip = (int)_ctx_start; 158 } 159 } 160