/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2006, David Xu <davidxu@freebsd.org>
 * 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 unmodified, 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.
 */

 /*
  * A lockless rwlock for rtld.
  */
#include <sys/mman.h>
#include <sys/syscall.h>
#include <link.h>
#include <stdlib.h>
#include <string.h>

#include "libc_private.h"
#include "rtld_lock.h"
#include "thr_private.h"

extern int __libsys_errno;

static int      _thr_rtld_clr_flag(int);
static void     *_thr_rtld_lock_create(void);
static void     _thr_rtld_lock_destroy(void *);
static void     _thr_rtld_lock_release(void *);
static void     _thr_rtld_rlock_acquire(void *);
static int      _thr_rtld_set_flag(int);
static void     _thr_rtld_wlock_acquire(void *);

struct rtld_lock {
        struct urwlock lock;
        struct pthread *wowner;
        u_int rlocks;
        char _pad[CACHE_LINE_SIZE - sizeof(struct urwlock) -
            sizeof(struct pthread *) - sizeof(u_int)];
};

static struct rtld_lock lock_place[MAX_RTLD_LOCKS] __aligned(CACHE_LINE_SIZE);
static int busy_places;

static void *
_thr_rtld_lock_create(void)
{
        int locki;
        struct rtld_lock *l;
        static const char fail[] = "_thr_rtld_lock_create failed\n";

        for (locki = 0; locki < MAX_RTLD_LOCKS; locki++) {
                if ((busy_places & (1 << locki)) == 0)
                        break;
        }
        if (locki == MAX_RTLD_LOCKS) {
                write(2, fail, sizeof(fail) - 1);
                return (NULL);
        }
        busy_places |= (1 << locki);

        l = &lock_place[locki];
        l->lock.rw_flags = URWLOCK_PREFER_READER;
        return (l);
}

static void
_thr_rtld_lock_destroy(void *lock)
{
        int locki;
        size_t i;

        locki = (struct rtld_lock *)lock - &lock_place[0];
        for (i = 0; i < sizeof(struct rtld_lock); ++i)
                ((char *)lock)[i] = 0;
        busy_places &= ~(1 << locki);
}

#define SAVE_ERRNO()    {                       \
        if (curthread != _thr_initial)          \
                errsave = curthread->error;     \
        else                                    \
                errsave = __libsys_errno;       \
}

#define RESTORE_ERRNO() {                       \
        if (curthread != _thr_initial)          \
                curthread->error = errsave;     \
        else                                    \
                __libsys_errno = errsave;       \
}

static void
_thr_rtld_rlock_acquire(void *lock)
{
        struct pthread          *curthread;
        struct rtld_lock        *l;
        int                     errsave;

        curthread = _get_curthread();
        SAVE_ERRNO();
        l = (struct rtld_lock *)lock;

        if (l->wowner == curthread) {
                l->rlocks++;
        } else {
                THR_CRITICAL_ENTER(curthread);
                while (_thr_rwlock_rdlock(&l->lock, 0, NULL) != 0)
                        ;
        }
        curthread->rdlock_count++;
        RESTORE_ERRNO();
}

static void
_thr_rtld_wlock_acquire(void *lock)
{
        struct pthread          *curthread;
        struct rtld_lock        *l;
        int                     errsave;

        curthread = _get_curthread();
        SAVE_ERRNO();
        l = (struct rtld_lock *)lock;

        THR_CRITICAL_ENTER(curthread);
        while (_thr_rwlock_wrlock(&l->lock, NULL) != 0)
                ;
        l->wowner = curthread;
        RESTORE_ERRNO();
}

static void
_thr_rtld_lock_release(void *lock)
{
        struct pthread          *curthread;
        struct rtld_lock        *l;
        int32_t                 state;
        int                     errsave;

        curthread = _get_curthread();
        SAVE_ERRNO();
        l = (struct rtld_lock *)lock;
        
        state = l->lock.rw_state;
        if (__predict_false(_thr_after_fork)) {
                /*
                 * After fork, only this thread is running, there is no
                 * waiters.  Keeping waiters recorded in rwlock breaks
                 * wake logic.
                 */
                atomic_clear_int(&l->lock.rw_state,
                    URWLOCK_WRITE_WAITERS | URWLOCK_READ_WAITERS);
                l->lock.rw_blocked_readers = 0;
                l->lock.rw_blocked_writers = 0;
        }
        if ((state & URWLOCK_WRITE_OWNER) != 0) {
                if (l->rlocks > 0) {
                        l->rlocks--;
                        return;
                } else {
                        l->wowner = NULL;
                }
        }
        if (_thr_rwlock_unlock(&l->lock) == 0) {
                if ((state & URWLOCK_WRITE_OWNER) == 0)
                        curthread->rdlock_count--;
                THR_CRITICAL_LEAVE(curthread);
        }
        RESTORE_ERRNO();
}

static int
_thr_rtld_set_flag(int mask __unused)
{
        /*
         * The caller's code in rtld-elf is broken, it is not signal safe,
         * just return zero to fool it.
         */
        return (0);
}

static int
_thr_rtld_clr_flag(int mask __unused)
{
        return (0);
}

/*
 * ABI bug workaround: This symbol must be present for rtld to accept
 * RTLI_VERSION from RtldLockInfo
 */
extern char _pli_rtli_version;
char _pli_rtli_version;

static char *
_thr_dlerror_loc(void)
{
        struct pthread *curthread;

        curthread = _get_curthread();
        return (curthread->dlerror_msg);
}

static int *
_thr_dlerror_seen(void)
{
        struct pthread *curthread;

        curthread = _get_curthread();
        return (&curthread->dlerror_seen);
}

void
_thr_rtld_init(void)
{
        struct RtldLockInfo     li;
        struct pthread          *curthread;
        ucontext_t *uc;
        int uc_len;
        char dummy[2] = {};

        curthread = _get_curthread();

        /* force to resolve _umtx_op PLT */
        _umtx_op_err(&dummy, UMTX_OP_WAKE, 1, 0, 0);
        
        /* force to resolve errno() PLT */
        __error();

        /* force to resolve memcpy PLT */
        memcpy(&dummy[0], &dummy[1], 1);

        mprotect(NULL, 0, 0);
        _rtld_get_stack_prot();
        thr_wake(-1);

        li.rtli_version = RTLI_VERSION;
        li.lock_create  = _thr_rtld_lock_create;
        li.lock_destroy = _thr_rtld_lock_destroy;
        li.rlock_acquire = _thr_rtld_rlock_acquire;
        li.wlock_acquire = _thr_rtld_wlock_acquire;
        li.lock_release  = _thr_rtld_lock_release;
        li.thread_set_flag = _thr_rtld_set_flag;
        li.thread_clr_flag = _thr_rtld_clr_flag;
        li.at_fork = NULL;
        li.dlerror_loc = _thr_dlerror_loc;
        li.dlerror_loc_sz = sizeof(curthread->dlerror_msg);
        li.dlerror_seen = _thr_dlerror_seen;

        /*
         * Preresolve the symbols needed for the fork interposer.  We
         * call _rtld_atfork_pre() and _rtld_atfork_post() with NULL
         * argument to indicate that no actual locking inside the
         * functions should happen.  Neither rtld compat locks nor
         * libthr rtld locks cannot work there:
         * - compat locks do not handle the case of two locks taken
         *   in write mode (the signal mask for the thread is corrupted);
         * - libthr locks would work, but locked rtld_bind_lock prevents
         *   symbol resolution for _rtld_atfork_post.
         */
        _rtld_atfork_pre(NULL);
        _rtld_atfork_post(NULL);
        _malloc_prefork();
        _malloc_postfork();
        getpid();
        syscall(SYS_getpid);

        /* mask signals, also force to resolve __sys_sigprocmask PLT */
        _thr_signal_block(curthread);
        _rtld_thread_init(&li);
        _thr_signal_unblock(curthread);
        _thr_signal_block_check_fast();
        _thr_signal_block_setup(curthread);

        /* resolve machine depended functions, if any */
        _thr_resolve_machdep();

        uc_len = __getcontextx_size();
        uc = alloca(uc_len);
        getcontext(uc);
        __fillcontextx2((char *)uc);
}