1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2003 Marcel Moolenaar 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 * 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 */ 28 29 #include <sys/cdefs.h> 30 #include <sys/types.h> 31 #include <sys/ucontext.h> 32 #include <stdarg.h> 33 #include <stdlib.h> 34 35 typedef void (*func_t)(uint64_t, uint64_t, uint64_t, uint64_t, uint64_t, 36 uint64_t); 37 38 /* Prototypes */ 39 static void makectx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args); 40 41 __weak_reference(__makecontext, makecontext); 42 43 void 44 __makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...) 45 { 46 uint64_t *args; 47 uint64_t *sp; 48 va_list ap; 49 int i; 50 51 /* A valid context is required. */ 52 if ((ucp == NULL) || (ucp->uc_mcontext.mc_len != sizeof(mcontext_t))) 53 return; 54 else if ((argc < 0) || (argc > 6) || (ucp->uc_stack.ss_sp == NULL) || 55 (ucp->uc_stack.ss_size < MINSIGSTKSZ)) { 56 /* 57 * This should really return -1 with errno set to ENOMEM 58 * or something, but the spec says that makecontext is 59 * a void function. At least make sure that the context 60 * isn't valid so it can't be used without an error. 61 */ 62 ucp->uc_mcontext.mc_len = 0; 63 return; 64 } 65 66 /* Align the stack to 16 bytes. */ 67 sp = (uint64_t *)(ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size); 68 sp = (uint64_t *)((uint64_t)sp & ~15UL); 69 70 /* Allocate space for a maximum of 6 arguments on the stack. */ 71 args = sp - 6; 72 73 /* 74 * Account for arguments on stack and do the funky C entry alignment. 75 * This means that we need an 8-byte-odd alignment since the ABI expects 76 * the return address to be pushed, thus breaking the 16 byte alignment. 77 */ 78 sp -= 7; 79 80 /* Add the arguments: */ 81 va_start(ap, argc); 82 for (i = 0; i < argc; i++) 83 args[i] = va_arg(ap, uint64_t); 84 va_end(ap); 85 for (i = argc; i < 6; i++) 86 args[i] = 0; 87 88 ucp->uc_mcontext.mc_rdi = (register_t)ucp; 89 ucp->uc_mcontext.mc_rsi = (register_t)start; 90 ucp->uc_mcontext.mc_rdx = (register_t)args; 91 ucp->uc_mcontext.mc_rbp = 0; 92 ucp->uc_mcontext.mc_rbx = (register_t)sp; 93 ucp->uc_mcontext.mc_rsp = (register_t)sp; 94 ucp->uc_mcontext.mc_rip = (register_t)makectx_wrapper; 95 } 96 97 static void 98 makectx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args) 99 { 100 (*func)(args[0], args[1], args[2], args[3], args[4], args[5]); 101 if (ucp->uc_link == NULL) 102 exit(0); 103 setcontext((const ucontext_t *)ucp->uc_link); 104 /* should never get here */ 105 abort(); 106 /* NOTREACHED */ 107 } 108