FreeBSD-5.3/libexec/rtld-elf/rtld_lock.c
/*-
* Copyright 1999, 2000 John D. Polstra.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* from: FreeBSD: src/libexec/rtld-elf/sparc64/lockdflt.c,v 1.3 2002/10/09
* $FreeBSD: src/libexec/rtld-elf/rtld_lock.c,v 1.2 2004/07/04 16:11:01 stefanf Exp $
*/
/*
* Thread locking implementation for the dynamic linker.
*
* We use the "simple, non-scalable reader-preference lock" from:
*
* J. M. Mellor-Crummey and M. L. Scott. "Scalable Reader-Writer
* Synchronization for Shared-Memory Multiprocessors." 3rd ACM Symp. on
* Principles and Practice of Parallel Programming, April 1991.
*
* In this algorithm the lock is a single word. Its low-order bit is
* set when a writer holds the lock. The remaining high-order bits
* contain a count of readers desiring the lock. The algorithm requires
* atomic "compare_and_store" and "add" operations, which we implement
* using assembly language sequences in "rtld_start.S".
*/
#include <signal.h>
#include <stdlib.h>
#include <time.h>
#include "debug.h"
#include "rtld.h"
#include "rtld_machdep.h"
#define WAFLAG 0x1 /* A writer holds the lock */
#define RC_INCR 0x2 /* Adjusts count of readers desiring lock */
typedef struct Struct_Lock {
volatile int lock;
void *base;
} Lock;
static sigset_t fullsigmask, oldsigmask;
static int thread_flag;
static void *
def_lock_create()
{
void *base;
char *p;
uintptr_t r;
Lock *l;
/*
* Arrange for the lock to occupy its own cache line. First, we
* optimistically allocate just a cache line, hoping that malloc
* will give us a well-aligned block of memory. If that doesn't
* work, we allocate a larger block and take a well-aligned cache
* line from it.
*/
base = xmalloc(CACHE_LINE_SIZE);
p = (char *)base;
if ((uintptr_t)p % CACHE_LINE_SIZE != 0) {
free(base);
base = xmalloc(2 * CACHE_LINE_SIZE);
p = (char *)base;
if ((r = (uintptr_t)p % CACHE_LINE_SIZE) != 0)
p += CACHE_LINE_SIZE - r;
}
l = (Lock *)p;
l->base = base;
l->lock = 0;
return l;
}
static void
def_lock_destroy(void *lock)
{
Lock *l = (Lock *)lock;
free(l->base);
}
static void
def_rlock_acquire(void *lock)
{
Lock *l = (Lock *)lock;
atomic_add_acq_int(&l->lock, RC_INCR);
while (l->lock & WAFLAG)
; /* Spin */
}
static void
def_wlock_acquire(void *lock)
{
Lock *l = (Lock *)lock;
sigset_t tmp_oldsigmask;
for ( ; ; ) {
sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
break;
sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
}
oldsigmask = tmp_oldsigmask;
}
static void
def_lock_release(void *lock)
{
Lock *l = (Lock *)lock;
if ((l->lock & WAFLAG) == 0)
atomic_add_rel_int(&l->lock, -RC_INCR);
else {
atomic_add_rel_int(&l->lock, -WAFLAG);
sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
}
}
#if __i386__
/*
* Import a crude exclusive lock implementation for i386 processors.
* This file will be removed once i386 support is deprecated in favor
* of i486+.
*/
#include "i386/lockdflt.c"
#endif
static int
def_thread_set_flag(int mask)
{
int old_val = thread_flag;
thread_flag |= mask;
return (old_val);
}
static int
def_thread_clr_flag(int mask)
{
int old_val = thread_flag;
thread_flag &= ~mask;
return (old_val);
}
/*
* Public interface exposed to the rest of the dynamic linker.
*/
static struct RtldLockInfo lockinfo;
static struct RtldLockInfo deflockinfo;
static __inline int
thread_mask_set(int mask)
{
return lockinfo.thread_set_flag(mask);
}
static __inline void
thread_mask_clear(int mask)
{
lockinfo.thread_clr_flag(mask);
}
#define RTLD_LOCK_CNT 2
struct rtld_lock {
void *handle;
int mask;
} rtld_locks[RTLD_LOCK_CNT];
rtld_lock_t rtld_bind_lock = &rtld_locks[0];
rtld_lock_t rtld_libc_lock = &rtld_locks[1];
int
rlock_acquire(rtld_lock_t lock)
{
if (thread_mask_set(lock->mask)) {
dbg("rlock_acquire: recursed");
return (0);
}
lockinfo.rlock_acquire(lock->handle);
return (1);
}
int
wlock_acquire(rtld_lock_t lock)
{
if (thread_mask_set(lock->mask)) {
dbg("wlock_acquire: recursed");
return (0);
}
lockinfo.wlock_acquire(lock->handle);
return (1);
}
void
rlock_release(rtld_lock_t lock, int locked)
{
if (locked == 0)
return;
thread_mask_clear(lock->mask);
lockinfo.lock_release(lock->handle);
}
void
wlock_release(rtld_lock_t lock, int locked)
{
if (locked == 0)
return;
thread_mask_clear(lock->mask);
lockinfo.lock_release(lock->handle);
}
void
lockdflt_init()
{
int i;
deflockinfo.rtli_version = RTLI_VERSION;
deflockinfo.lock_create = def_lock_create;
deflockinfo.lock_destroy = def_lock_destroy;
deflockinfo.rlock_acquire = def_rlock_acquire;
deflockinfo.wlock_acquire = def_wlock_acquire;
deflockinfo.lock_release = def_lock_release;
deflockinfo.thread_set_flag = def_thread_set_flag;
deflockinfo.thread_clr_flag = def_thread_clr_flag;
deflockinfo.at_fork = NULL;
for (i = 0; i < RTLD_LOCK_CNT; i++) {
rtld_locks[i].mask = (1 << i);
rtld_locks[i].handle = NULL;
}
#if __i386__
if (!cpu_supports_cmpxchg()) {
/* It's a cruddy old 80386. */
deflockinfo.rlock_acquire = lock80386_acquire;
deflockinfo.wlock_acquire = lock80386_acquire;
deflockinfo.lock_release = lock80386_release;
}
#endif
memcpy(&lockinfo, &deflockinfo, sizeof(lockinfo));
_rtld_thread_init(NULL);
/*
* Construct a mask to block all signals except traps which might
* conceivably be generated within the dynamic linker itself.
*/
sigfillset(&fullsigmask);
sigdelset(&fullsigmask, SIGILL);
sigdelset(&fullsigmask, SIGTRAP);
sigdelset(&fullsigmask, SIGABRT);
sigdelset(&fullsigmask, SIGEMT);
sigdelset(&fullsigmask, SIGFPE);
sigdelset(&fullsigmask, SIGBUS);
sigdelset(&fullsigmask, SIGSEGV);
sigdelset(&fullsigmask, SIGSYS);
}
/*
* Callback function to allow threads implementation to
* register their own locking primitives if the default
* one is not suitable.
* The current context should be the only context
* executing at the invocation time.
*/
void
_rtld_thread_init(struct RtldLockInfo *pli)
{
int flags, i;
void *locks[RTLD_LOCK_CNT];
/* disable all locking while this function is running */
flags = thread_mask_set(~0);
if (pli == NULL)
pli = &deflockinfo;
for (i = 0; i < RTLD_LOCK_CNT; i++)
if ((locks[i] = pli->lock_create()) == NULL)
break;
if (i < RTLD_LOCK_CNT) {
while (--i >= 0)
pli->lock_destroy(locks[i]);
abort();
}
for (i = 0; i < RTLD_LOCK_CNT; i++) {
if (rtld_locks[i].handle == NULL)
continue;
if (flags & rtld_locks[i].mask)
lockinfo.lock_release(rtld_locks[i].handle);
lockinfo.lock_destroy(rtld_locks[i].handle);
}
for (i = 0; i < RTLD_LOCK_CNT; i++) {
rtld_locks[i].handle = locks[i];
if (flags & rtld_locks[i].mask)
pli->wlock_acquire(rtld_locks[i].handle);
}
lockinfo.lock_create = pli->lock_create;
lockinfo.lock_destroy = pli->lock_destroy;
lockinfo.rlock_acquire = pli->rlock_acquire;
lockinfo.wlock_acquire = pli->wlock_acquire;
lockinfo.lock_release = pli->lock_release;
lockinfo.thread_set_flag = pli->thread_set_flag;
lockinfo.thread_clr_flag = pli->thread_clr_flag;
lockinfo.at_fork = pli->at_fork;
/* restore thread locking state, this time with new locks */
thread_mask_clear(~0);
thread_mask_set(flags);
dbg("_rtld_thread_init: done");
}