1 /* 2 * Copyright (c) 2006, David Xu <davidxu@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 unmodified, this list of conditions, and the following 10 * disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27 #include <sys/cdefs.h> 28 __FBSDID("$FreeBSD$"); 29 30 /* 31 * A lockless rwlock for rtld. 32 */ 33 #include <sys/cdefs.h> 34 #include <sys/mman.h> 35 #include <sys/syscall.h> 36 #include <link.h> 37 #include <stdlib.h> 38 #include <string.h> 39 40 #include "libc_private.h" 41 #include "rtld_lock.h" 42 #include "thr_private.h" 43 44 #undef errno 45 extern int errno; 46 47 static int _thr_rtld_clr_flag(int); 48 static void *_thr_rtld_lock_create(void); 49 static void _thr_rtld_lock_destroy(void *); 50 static void _thr_rtld_lock_release(void *); 51 static void _thr_rtld_rlock_acquire(void *); 52 static int _thr_rtld_set_flag(int); 53 static void _thr_rtld_wlock_acquire(void *); 54 55 struct rtld_lock { 56 struct urwlock lock; 57 char _pad[CACHE_LINE_SIZE - sizeof(struct urwlock)]; 58 }; 59 60 static struct rtld_lock lock_place[MAX_RTLD_LOCKS] __aligned(CACHE_LINE_SIZE); 61 static int busy_places; 62 63 static void * 64 _thr_rtld_lock_create(void) 65 { 66 int locki; 67 struct rtld_lock *l; 68 static const char fail[] = "_thr_rtld_lock_create failed\n"; 69 70 for (locki = 0; locki < MAX_RTLD_LOCKS; locki++) { 71 if ((busy_places & (1 << locki)) == 0) 72 break; 73 } 74 if (locki == MAX_RTLD_LOCKS) { 75 write(2, fail, sizeof(fail) - 1); 76 return (NULL); 77 } 78 busy_places |= (1 << locki); 79 80 l = &lock_place[locki]; 81 l->lock.rw_flags = URWLOCK_PREFER_READER; 82 return (l); 83 } 84 85 static void 86 _thr_rtld_lock_destroy(void *lock) 87 { 88 int locki; 89 size_t i; 90 91 locki = (struct rtld_lock *)lock - &lock_place[0]; 92 for (i = 0; i < sizeof(struct rtld_lock); ++i) 93 ((char *)lock)[i] = 0; 94 busy_places &= ~(1 << locki); 95 } 96 97 #define SAVE_ERRNO() { \ 98 if (curthread != _thr_initial) \ 99 errsave = curthread->error; \ 100 else \ 101 errsave = errno; \ 102 } 103 104 #define RESTORE_ERRNO() { \ 105 if (curthread != _thr_initial) \ 106 curthread->error = errsave; \ 107 else \ 108 errno = errsave; \ 109 } 110 111 static void 112 _thr_rtld_rlock_acquire(void *lock) 113 { 114 struct pthread *curthread; 115 struct rtld_lock *l; 116 int errsave; 117 118 curthread = _get_curthread(); 119 SAVE_ERRNO(); 120 l = (struct rtld_lock *)lock; 121 122 THR_CRITICAL_ENTER(curthread); 123 while (_thr_rwlock_rdlock(&l->lock, 0, NULL) != 0) 124 ; 125 curthread->rdlock_count++; 126 RESTORE_ERRNO(); 127 } 128 129 static void 130 _thr_rtld_wlock_acquire(void *lock) 131 { 132 struct pthread *curthread; 133 struct rtld_lock *l; 134 int errsave; 135 136 curthread = _get_curthread(); 137 SAVE_ERRNO(); 138 l = (struct rtld_lock *)lock; 139 140 THR_CRITICAL_ENTER(curthread); 141 while (_thr_rwlock_wrlock(&l->lock, NULL) != 0) 142 ; 143 RESTORE_ERRNO(); 144 } 145 146 static void 147 _thr_rtld_lock_release(void *lock) 148 { 149 struct pthread *curthread; 150 struct rtld_lock *l; 151 int32_t state; 152 int errsave; 153 154 curthread = _get_curthread(); 155 SAVE_ERRNO(); 156 l = (struct rtld_lock *)lock; 157 158 state = l->lock.rw_state; 159 if (_thr_rwlock_unlock(&l->lock) == 0) { 160 if ((state & URWLOCK_WRITE_OWNER) == 0) 161 curthread->rdlock_count--; 162 THR_CRITICAL_LEAVE(curthread); 163 } 164 RESTORE_ERRNO(); 165 } 166 167 static int 168 _thr_rtld_set_flag(int mask __unused) 169 { 170 /* 171 * The caller's code in rtld-elf is broken, it is not signal safe, 172 * just return zero to fool it. 173 */ 174 return (0); 175 } 176 177 static int 178 _thr_rtld_clr_flag(int mask __unused) 179 { 180 return (0); 181 } 182 183 void 184 _thr_rtld_init(void) 185 { 186 struct RtldLockInfo li; 187 struct pthread *curthread; 188 ucontext_t *uc; 189 long dummy = -1; 190 int uc_len; 191 192 curthread = _get_curthread(); 193 194 /* force to resolve _umtx_op PLT */ 195 _umtx_op_err((struct umtx *)&dummy, UMTX_OP_WAKE, 1, 0, 0); 196 197 /* force to resolve errno() PLT */ 198 __error(); 199 200 /* force to resolve memcpy PLT */ 201 memcpy(&dummy, &dummy, sizeof(dummy)); 202 203 mprotect(NULL, 0, 0); 204 _rtld_get_stack_prot(); 205 206 li.lock_create = _thr_rtld_lock_create; 207 li.lock_destroy = _thr_rtld_lock_destroy; 208 li.rlock_acquire = _thr_rtld_rlock_acquire; 209 li.wlock_acquire = _thr_rtld_wlock_acquire; 210 li.lock_release = _thr_rtld_lock_release; 211 li.thread_set_flag = _thr_rtld_set_flag; 212 li.thread_clr_flag = _thr_rtld_clr_flag; 213 li.at_fork = NULL; 214 215 /* 216 * Preresolve the symbols needed for the fork interposer. We 217 * call _rtld_atfork_pre() and _rtld_atfork_post() with NULL 218 * argument to indicate that no actual locking inside the 219 * functions should happen. Neither rtld compat locks nor 220 * libthr rtld locks cannot work there: 221 * - compat locks do not handle the case of two locks taken 222 * in write mode (the signal mask for the thread is corrupted); 223 * - libthr locks would work, but locked rtld_bind_lock prevents 224 * symbol resolution for _rtld_atfork_post. 225 */ 226 _rtld_atfork_pre(NULL); 227 _rtld_atfork_post(NULL); 228 _malloc_prefork(); 229 _malloc_postfork(); 230 getpid(); 231 syscall(SYS_getpid); 232 233 /* mask signals, also force to resolve __sys_sigprocmask PLT */ 234 _thr_signal_block(curthread); 235 _rtld_thread_init(&li); 236 _thr_signal_unblock(curthread); 237 238 uc_len = __getcontextx_size(); 239 uc = alloca(uc_len); 240 getcontext(uc); 241 __fillcontextx2((char *)uc); 242 } 243