/*-
 * 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) != 0) {
                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) != 0) {
                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);
        }
}

bool
lockstate_wlocked(const RtldLockState *lockstate)
{
        return (lockstate->lockstate == RTLD_LOCK_WLOCKED);
}

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;
        bzero(ls, sizeof(ls));

        /*
         * 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.
         */
        if (ld_get_env_var(LD_NO_DL_ITERATE_PHDR_AFTER_FORK) == NULL)
                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]);
        if (ld_get_env_var(LD_NO_DL_ITERATE_PHDR_AFTER_FORK) == NULL)
                lock_release(rtld_phdr_lock, &ls[0]);
}