util/getauxval.c

/*
 * QEMU access to the auxiliary vector
 *
 * Copyright (C) 2013 Red Hat, Inc
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "qemu-common.h"
#include "qemu/osdep.h"

#ifdef CONFIG_GETAUXVAL
/* Don't inline this in qemu/osdep.h, because pulling in <sys/auxv.h> for
   the system declaration of getauxval pulls in the system <elf.h>, which
   conflicts with qemu's version.  */

#include <sys/auxv.h>

unsigned long qemu_getauxval(unsigned long key)
{
    return getauxval(key);
}
#elif defined(__linux__)
#include "elf.h"

/* Our elf.h doesn't contain Elf32_auxv_t and Elf64_auxv_t, which is ok because
   that just makes it easier to define it properly for the host here.  */
typedef struct {
    unsigned long a_type;
    unsigned long a_val;
} ElfW_auxv_t;

static const ElfW_auxv_t *auxv;

static const ElfW_auxv_t *qemu_init_auxval(void)
{
    ElfW_auxv_t *a;
    ssize_t size = 512, r, ofs;
    int fd;

    /* Allocate some initial storage.  Make sure the first entry is set
       to end-of-list, so that we've got a valid list in case of error.  */
    auxv = a = g_malloc(size);
    a[0].a_type = 0;
    a[0].a_val = 0;

    fd = open("/proc/self/auxv", O_RDONLY);
    if (fd < 0) {
        return a;
    }

    /* Read the first SIZE bytes.  Hopefully, this covers everything.  */
    r = read(fd, a, size);

    if (r == size) {
        /* Continue to expand until we do get a partial read.  */
        do {
            ofs = size;
            size *= 2;
            auxv = a = g_realloc(a, size);
            r = read(fd, (char *)a + ofs, ofs);
        } while (r == ofs);
    }

    close(fd);
    return a;
}

unsigned long qemu_getauxval(unsigned long type)
{
    const ElfW_auxv_t *a = auxv;

    if (unlikely(a == NULL)) {
        a = qemu_init_auxval();
    }

    for (; a->a_type != 0; a++) {
        if (a->a_type == type) {
            return a->a_val;
        }
    }

    return 0;
}
#endif