2 * Copyright 1999, 2000 John D. Polstra.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 * from: FreeBSD: src/libexec/rtld-elf/sparc64/lockdflt.c,v 1.3 2002/10/09
30 * Thread locking implementation for the dynamic linker.
32 * We use the "simple, non-scalable reader-preference lock" from:
34 * J. M. Mellor-Crummey and M. L. Scott. "Scalable Reader-Writer
35 * Synchronization for Shared-Memory Multiprocessors." 3rd ACM Symp. on
36 * Principles and Practice of Parallel Programming, April 1991.
38 * In this algorithm the lock is a single word. Its low-order bit is
39 * set when a writer holds the lock. The remaining high-order bits
40 * contain a count of readers desiring the lock. The algorithm requires
41 * atomic "compare_and_store" and "add" operations, which we implement
42 * using assembly language sequences in "rtld_start.S".
51 #include "rtld_machdep.h"
53 #define WAFLAG 0x1 /* A writer holds the lock */
54 #define RC_INCR 0x2 /* Adjusts count of readers desiring lock */
56 typedef struct Struct_Lock {
61 static sigset_t fullsigmask, oldsigmask;
62 static int thread_flag;
73 * Arrange for the lock to occupy its own cache line. First, we
74 * optimistically allocate just a cache line, hoping that malloc
75 * will give us a well-aligned block of memory. If that doesn't
76 * work, we allocate a larger block and take a well-aligned cache
79 base = xmalloc(CACHE_LINE_SIZE);
81 if ((uintptr_t)p % CACHE_LINE_SIZE != 0) {
83 base = xmalloc(2 * CACHE_LINE_SIZE);
85 if ((r = (uintptr_t)p % CACHE_LINE_SIZE) != 0)
86 p += CACHE_LINE_SIZE - r;
95 def_lock_destroy(void *lock)
97 Lock *l = (Lock *)lock;
103 def_rlock_acquire(void *lock)
105 Lock *l = (Lock *)lock;
107 atomic_add_acq_int(&l->lock, RC_INCR);
108 while (l->lock & WAFLAG)
113 def_wlock_acquire(void *lock)
115 Lock *l = (Lock *)lock;
116 sigset_t tmp_oldsigmask;
119 sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
120 if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
122 sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
124 oldsigmask = tmp_oldsigmask;
128 def_lock_release(void *lock)
130 Lock *l = (Lock *)lock;
132 if ((l->lock & WAFLAG) == 0)
133 atomic_add_rel_int(&l->lock, -RC_INCR);
135 atomic_add_rel_int(&l->lock, -WAFLAG);
136 sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
141 def_thread_set_flag(int mask)
143 int old_val = thread_flag;
149 def_thread_clr_flag(int mask)
151 int old_val = thread_flag;
152 thread_flag &= ~mask;
157 * Public interface exposed to the rest of the dynamic linker.
159 static struct RtldLockInfo lockinfo;
160 static struct RtldLockInfo deflockinfo;
163 thread_mask_set(int mask)
165 return lockinfo.thread_set_flag(mask);
169 thread_mask_clear(int mask)
171 lockinfo.thread_clr_flag(mask);
174 #define RTLD_LOCK_CNT 2
178 } rtld_locks[RTLD_LOCK_CNT];
180 rtld_lock_t rtld_bind_lock = &rtld_locks[0];
181 rtld_lock_t rtld_libc_lock = &rtld_locks[1];
184 rlock_acquire(rtld_lock_t lock)
186 if (thread_mask_set(lock->mask)) {
187 dbg("rlock_acquire: recursed");
190 lockinfo.rlock_acquire(lock->handle);
195 wlock_acquire(rtld_lock_t lock)
197 if (thread_mask_set(lock->mask)) {
198 dbg("wlock_acquire: recursed");
201 lockinfo.wlock_acquire(lock->handle);
206 rlock_release(rtld_lock_t lock, int locked)
210 thread_mask_clear(lock->mask);
211 lockinfo.lock_release(lock->handle);
215 wlock_release(rtld_lock_t lock, int locked)
219 thread_mask_clear(lock->mask);
220 lockinfo.lock_release(lock->handle);
228 deflockinfo.rtli_version = RTLI_VERSION;
229 deflockinfo.lock_create = def_lock_create;
230 deflockinfo.lock_destroy = def_lock_destroy;
231 deflockinfo.rlock_acquire = def_rlock_acquire;
232 deflockinfo.wlock_acquire = def_wlock_acquire;
233 deflockinfo.lock_release = def_lock_release;
234 deflockinfo.thread_set_flag = def_thread_set_flag;
235 deflockinfo.thread_clr_flag = def_thread_clr_flag;
236 deflockinfo.at_fork = NULL;
238 for (i = 0; i < RTLD_LOCK_CNT; i++) {
239 rtld_locks[i].mask = (1 << i);
240 rtld_locks[i].handle = NULL;
243 memcpy(&lockinfo, &deflockinfo, sizeof(lockinfo));
244 _rtld_thread_init(NULL);
246 * Construct a mask to block all signals except traps which might
247 * conceivably be generated within the dynamic linker itself.
249 sigfillset(&fullsigmask);
250 sigdelset(&fullsigmask, SIGILL);
251 sigdelset(&fullsigmask, SIGTRAP);
252 sigdelset(&fullsigmask, SIGABRT);
253 sigdelset(&fullsigmask, SIGEMT);
254 sigdelset(&fullsigmask, SIGFPE);
255 sigdelset(&fullsigmask, SIGBUS);
256 sigdelset(&fullsigmask, SIGSEGV);
257 sigdelset(&fullsigmask, SIGSYS);
261 * Callback function to allow threads implementation to
262 * register their own locking primitives if the default
263 * one is not suitable.
264 * The current context should be the only context
265 * executing at the invocation time.
268 _rtld_thread_init(struct RtldLockInfo *pli)
271 void *locks[RTLD_LOCK_CNT];
273 /* disable all locking while this function is running */
274 flags = thread_mask_set(~0);
280 for (i = 0; i < RTLD_LOCK_CNT; i++)
281 if ((locks[i] = pli->lock_create()) == NULL)
284 if (i < RTLD_LOCK_CNT) {
286 pli->lock_destroy(locks[i]);
290 for (i = 0; i < RTLD_LOCK_CNT; i++) {
291 if (rtld_locks[i].handle == NULL)
293 if (flags & rtld_locks[i].mask)
294 lockinfo.lock_release(rtld_locks[i].handle);
295 lockinfo.lock_destroy(rtld_locks[i].handle);
298 for (i = 0; i < RTLD_LOCK_CNT; i++) {
299 rtld_locks[i].handle = locks[i];
300 if (flags & rtld_locks[i].mask)
301 pli->wlock_acquire(rtld_locks[i].handle);
304 lockinfo.lock_create = pli->lock_create;
305 lockinfo.lock_destroy = pli->lock_destroy;
306 lockinfo.rlock_acquire = pli->rlock_acquire;
307 lockinfo.wlock_acquire = pli->wlock_acquire;
308 lockinfo.lock_release = pli->lock_release;
309 lockinfo.thread_set_flag = pli->thread_set_flag;
310 lockinfo.thread_clr_flag = pli->thread_clr_flag;
311 lockinfo.at_fork = pli->at_fork;
313 /* restore thread locking state, this time with new locks */
314 thread_mask_clear(~0);
315 thread_mask_set(flags);
316 dbg("_rtld_thread_init: done");