port/sys/sbrk.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
 */

#pragma weak _sbrk = sbrk
#pragma weak _brk = brk

#include "lint.h"
#include <synch.h>
#include <errno.h>
#include <sys/isa_defs.h>
#include <sys/types.h>
#include <sys/sysmacros.h>
#include <inttypes.h>
#include <unistd.h>
#include "mtlib.h"
#include "libc.h"

void *_nd = NULL;
mutex_t __sbrk_lock = DEFAULTMUTEX;

extern intptr_t _brk_unlocked(void *);
extern void *_sbrk_unlocked(intptr_t);

/*
 * The break must always be at least 8-byte aligned
 */
#if (_MAX_ALIGNMENT < 8)
#define ALIGNSZ     8
#else
#define ALIGNSZ     _MAX_ALIGNMENT
#endif

#define BRKALIGN(x) (caddr_t)P2ROUNDUP((uintptr_t)(x), ALIGNSZ)

void *
sbrk(intptr_t addend)
{
    void *result;

    if (!primary_link_map) {
        errno = ENOTSUP;
        return ((void *)-1);
    }
    lmutex_lock(&__sbrk_lock);
    result = _sbrk_unlocked(addend);
    lmutex_unlock(&__sbrk_lock);

    return (result);
}

/*
 * _sbrk_unlocked() aligns the old break, adds the addend, aligns
 * the new break, and calls _brk_unlocked() to set the new break.
 * We must align the old break because _nd may begin life misaligned.
 * The addend can be either positive or negative, so there are two
 * overflow/underflow edge conditions to reject:
 *
 *   - the addend is negative and brk + addend < 0.
 *   - the addend is positive and brk + addend > ULONG_MAX
 */
void *
_sbrk_unlocked(intptr_t addend)
{
    char *old_brk, *new_brk;

    if (_nd == NULL) {
        /*
         * Start of the data segment hasn't been calculated yet.
         * Use brk(0) to gather it from the kernel.
         */
        _nd = (void *)_brk_unlocked(0);
    }

    old_brk = BRKALIGN(_nd);
    new_brk = BRKALIGN(old_brk + addend);

    if ((addend > 0 && new_brk < old_brk) ||
        (addend < 0 && new_brk > old_brk)) {
        errno = ENOMEM;
        return ((void *)-1);
    }
    if (_brk_unlocked(new_brk) != 0)
        return ((void *)-1);
    _nd = new_brk;
    return (old_brk);
}

/*
 * _sbrk_grow_aligned() aligns the old break to a low_align boundry,
 * adds min_size, aligns to a high_align boundry, and calls _brk_unlocked()
 * to set the new break.  The low_aligned-aligned value is returned, and
 * the actual space allocated is returned through actual_size.
 *
 * Unlike sbrk(2), _sbrk_grow_aligned takes an unsigned size, and does
 * not allow shrinking the heap.
 */
void *
_sbrk_grow_aligned(size_t min_size, size_t low_align, size_t high_align,
    size_t *actual_size)
{
    uintptr_t old_brk;
    uintptr_t ret_brk;
    uintptr_t high_brk;
    uintptr_t new_brk;
    int brk_result;

    if (!primary_link_map) {
        errno = ENOTSUP;
        return ((void *)-1);
    }
    if ((low_align & (low_align - 1)) != 0 ||
        (high_align & (high_align - 1)) != 0) {
        errno = EINVAL;
        return ((void *)-1);
    }
    low_align = MAX(low_align, ALIGNSZ);
    high_align = MAX(high_align, ALIGNSZ);

    lmutex_lock(&__sbrk_lock);

    if (_nd == NULL) {
        /*
         * Start of the data segment hasn't been calculated yet.
         * Use brk(0) to gather it from the kernel.
         */
        _nd = (void *)_brk_unlocked(0);
    }

    old_brk = (uintptr_t)BRKALIGN(_nd);
    ret_brk = P2ROUNDUP(old_brk, low_align);
    high_brk = ret_brk + min_size;
    new_brk = P2ROUNDUP(high_brk, high_align);

    /*
     * Check for overflow
     */
    if (ret_brk < old_brk || high_brk < ret_brk || new_brk < high_brk) {
        lmutex_unlock(&__sbrk_lock);
        errno = ENOMEM;
        return ((void *)-1);
    }

    if ((brk_result = _brk_unlocked((void *)new_brk)) == 0)
        _nd = (void *)new_brk;
    lmutex_unlock(&__sbrk_lock);

    if (brk_result != 0)
        return ((void *)-1);

    if (actual_size != NULL)
        *actual_size = (new_brk - ret_brk);
    return ((void *)ret_brk);
}

int
brk(void *new_brk)
{
    intptr_t result;

    if (!primary_link_map) {
        errno = ENOTSUP;
        return (-1);
    }

    /*
     * Return what a call to brk(0) not going through the special path
     * would return.
     */
    if ((uintptr_t)new_brk == 0) {
        errno = ENOMEM;
        return (-1);
    }
    /*
     * Need to align this here;  _brk_unlocked won't do it for us.
     */
    new_brk = BRKALIGN(new_brk);

    lmutex_lock(&__sbrk_lock);
    if ((result = _brk_unlocked(new_brk)) == 0)
        _nd = new_brk;
    lmutex_unlock(&__sbrk_lock);

    return ((int)result);
}