freebsd-src/libexec/rtld-elf/rtld_lock.c
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497 lines
12 KiB
C

/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* 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
*/
/*
* 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 take
* from machine/atomic.h.
*/
#include <sys/param.h>
#include <sys/signalvar.h>
#include <signal.h>
#include <stdlib.h>
#include <time.h>
#include "debug.h"
#include "rtld.h"
#include "rtld_machdep.h"
#include "rtld_libc.h"
void _rtld_thread_init(struct RtldLockInfo *) __exported;
void _rtld_atfork_pre(int *) __exported;
void _rtld_atfork_post(int *) __exported;
static char def_dlerror_msg[512];
static int def_dlerror_seen_val = 1;
static char *
def_dlerror_loc(void)
{
return (def_dlerror_msg);
}
static int *
def_dlerror_seen(void)
{
return (&def_dlerror_seen_val);
}
#define WAFLAG 0x1 /* A writer holds the lock */
#define RC_INCR 0x2 /* Adjusts count of readers desiring lock */
typedef struct Struct_Lock {
volatile u_int lock;
void *base;
} Lock;
static sigset_t fullsigmask, oldsigmask;
static int thread_flag, wnested;
static uint32_t fsigblock;
static void *
def_lock_create(void)
{
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 = base;
if ((uintptr_t)p % CACHE_LINE_SIZE != 0) {
free(base);
base = xmalloc(2 * CACHE_LINE_SIZE);
p = 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;
free(l->base);
}
static void
sig_fastunblock(void)
{
uint32_t oldval;
assert((fsigblock & ~SIGFASTBLOCK_FLAGS) >= SIGFASTBLOCK_INC);
oldval = atomic_fetchadd_32(&fsigblock, -SIGFASTBLOCK_INC);
if (oldval == (SIGFASTBLOCK_PEND | SIGFASTBLOCK_INC))
__sys_sigfastblock(SIGFASTBLOCK_UNBLOCK, NULL);
}
static bool
def_lock_acquire_set(Lock *l, bool wlock)
{
if (wlock) {
if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
return (true);
} else {
atomic_add_acq_int(&l->lock, RC_INCR);
if ((l->lock & WAFLAG) == 0)
return (true);
atomic_add_int(&l->lock, -RC_INCR);
}
return (false);
}
static void
def_lock_acquire(Lock *l, bool wlock)
{
sigset_t tmp_oldsigmask;
if (ld_fast_sigblock) {
for (;;) {
atomic_add_32(&fsigblock, SIGFASTBLOCK_INC);
if (def_lock_acquire_set(l, wlock))
break;
sig_fastunblock();
}
} else {
for (;;) {
sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
if (def_lock_acquire_set(l, wlock))
break;
sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
}
if (atomic_fetchadd_int(&wnested, 1) == 0)
oldsigmask = tmp_oldsigmask;
}
}
static void
def_rlock_acquire(void *lock)
{
def_lock_acquire(lock, false);
}
static void
def_wlock_acquire(void *lock)
{
def_lock_acquire(lock, true);
}
static void
def_lock_release(void *lock)
{
Lock *l = lock;
atomic_add_rel_int(&l->lock, -((l->lock & WAFLAG) == 0 ?
RC_INCR : WAFLAG));
if (ld_fast_sigblock)
sig_fastunblock();
else if (atomic_fetchadd_int(&wnested, -1) == 1)
sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
}
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.
*/
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 3
static 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];
rtld_lock_t rtld_phdr_lock = &rtld_locks[2];
void
rlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
{
if (lockstate == NULL)
return;
if (thread_mask_set(lock->mask) & lock->mask) {
dbg("rlock_acquire: recursed");
lockstate->lockstate = RTLD_LOCK_UNLOCKED;
return;
}
lockinfo.rlock_acquire(lock->handle);
lockstate->lockstate = RTLD_LOCK_RLOCKED;
}
void
wlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
{
if (lockstate == NULL)
return;
if (thread_mask_set(lock->mask) & lock->mask) {
dbg("wlock_acquire: recursed");
lockstate->lockstate = RTLD_LOCK_UNLOCKED;
return;
}
lockinfo.wlock_acquire(lock->handle);
lockstate->lockstate = RTLD_LOCK_WLOCKED;
}
void
lock_release(rtld_lock_t lock, RtldLockState *lockstate)
{
if (lockstate == NULL)
return;
switch (lockstate->lockstate) {
case RTLD_LOCK_UNLOCKED:
break;
case RTLD_LOCK_RLOCKED:
case RTLD_LOCK_WLOCKED:
thread_mask_clear(lock->mask);
lockinfo.lock_release(lock->handle);
break;
default:
assert(0);
}
}
void
lock_upgrade(rtld_lock_t lock, RtldLockState *lockstate)
{
if (lockstate == NULL)
return;
lock_release(lock, lockstate);
wlock_acquire(lock, lockstate);
}
void
lock_restart_for_upgrade(RtldLockState *lockstate)
{
if (lockstate == NULL)
return;
switch (lockstate->lockstate) {
case RTLD_LOCK_UNLOCKED:
case RTLD_LOCK_WLOCKED:
break;
case RTLD_LOCK_RLOCKED:
siglongjmp(lockstate->env, 1);
break;
default:
assert(0);
}
}
void
dlerror_dflt_init(void)
{
lockinfo.dlerror_loc = def_dlerror_loc;
lockinfo.dlerror_loc_sz = sizeof(def_dlerror_msg);
lockinfo.dlerror_seen = def_dlerror_seen;
}
void
lockdflt_init(void)
{
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;
deflockinfo.dlerror_loc = def_dlerror_loc;
deflockinfo.dlerror_loc_sz = sizeof(def_dlerror_msg);
deflockinfo.dlerror_seen = def_dlerror_seen;
for (i = 0; i < RTLD_LOCK_CNT; i++) {
rtld_locks[i].mask = (1 << i);
rtld_locks[i].handle = NULL;
}
memcpy(&lockinfo, &deflockinfo, sizeof(lockinfo));
_rtld_thread_init(NULL);
if (ld_fast_sigblock) {
__sys_sigfastblock(SIGFASTBLOCK_SETPTR, &fsigblock);
} else {
/*
* Construct a mask to block all signals. Note that
* blocked traps mean that the process is terminated
* if trap occurs while we are in locked section, with
* the default settings for kern.forcesigexit.
*/
sigfillset(&fullsigmask);
}
}
/*
* 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)
{
const Obj_Entry *obj;
SymLook req;
void *locks[RTLD_LOCK_CNT];
int flags, i, res;
if (pli == NULL) {
lockinfo.rtli_version = RTLI_VERSION;
} else {
lockinfo.rtli_version = RTLI_VERSION_ONE;
obj = obj_from_addr(pli->lock_create);
if (obj != NULL) {
symlook_init(&req, "_pli_rtli_version");
res = symlook_obj(&req, obj);
if (res == 0)
lockinfo.rtli_version = pli->rtli_version;
}
}
/* disable all locking while this function is running */
flags = thread_mask_set(~0);
if (pli == NULL)
pli = &deflockinfo;
else if (ld_fast_sigblock) {
fsigblock = 0;
__sys_sigfastblock(SIGFASTBLOCK_UNSETPTR, NULL);
}
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;
if (lockinfo.rtli_version > RTLI_VERSION_ONE && pli != NULL) {
strlcpy(pli->dlerror_loc(), lockinfo.dlerror_loc(),
lockinfo.dlerror_loc_sz);
lockinfo.dlerror_loc = pli->dlerror_loc;
lockinfo.dlerror_loc_sz = pli->dlerror_loc_sz;
lockinfo.dlerror_seen = pli->dlerror_seen;
}
/* restore thread locking state, this time with new locks */
thread_mask_clear(~0);
thread_mask_set(flags);
dbg("_rtld_thread_init: done");
}
void
_rtld_atfork_pre(int *locks)
{
RtldLockState ls[2];
if (locks == NULL)
return;
/*
* Warning: this did not worked well with the rtld compat
* locks above, when the thread signal mask was corrupted (set
* to all signals blocked) if two locks were taken
* simultaneously in the write mode. The caller of the
* _rtld_atfork_pre() must provide the working implementation
* of the locks anyway, and libthr locks are fine.
*/
wlock_acquire(rtld_phdr_lock, &ls[0]);
wlock_acquire(rtld_bind_lock, &ls[1]);
/* XXXKIB: I am really sorry for this. */
locks[0] = ls[1].lockstate;
locks[2] = ls[0].lockstate;
}
void
_rtld_atfork_post(int *locks)
{
RtldLockState ls[2];
if (locks == NULL)
return;
bzero(ls, sizeof(ls));
ls[0].lockstate = locks[2];
ls[1].lockstate = locks[0];
lock_release(rtld_bind_lock, &ls[1]);
lock_release(rtld_phdr_lock, &ls[0]);
}