util/getauxval.c

   1 /*
   2  * QEMU access to the auxiliary vector
   3  *
   4  * Copyright (C) 2013 Red Hat, Inc
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu-common.h"
  26 #include "qemu/osdep.h"
  27
  28 #ifdef CONFIG_GETAUXVAL
  29 /* Don't inline this in qemu/osdep.h, because pulling in <sys/auxv.h> for
  30    the system declaration of getauxval pulls in the system <elf.h>, which
  31    conflicts with qemu's version.  */
  32
  33 #include <sys/auxv.h>
  34
  35 unsigned long qemu_getauxval(unsigned long key)
  36 {
  37     return getauxval(key);
  38 }
  39 #elif defined(__linux__)
  40 #include "elf.h"
  41
  42 /* Our elf.h doesn't contain Elf32_auxv_t and Elf64_auxv_t, which is ok because
  43    that just makes it easier to define it properly for the host here.  */
  44 typedef struct {
  45     unsigned long a_type;
  46     unsigned long a_val;
  47 } ElfW_auxv_t;
  48
  49 static const ElfW_auxv_t *auxv;
  50
  51 static const ElfW_auxv_t *qemu_init_auxval(void)
  52 {
  53     ElfW_auxv_t *a;
  54     ssize_t size = 512, r, ofs;
  55     int fd;
  56
  57     /* Allocate some initial storage.  Make sure the first entry is set
  58        to end-of-list, so that we've got a valid list in case of error.  */
  59     auxv = a = g_malloc(size);
  60     a[0].a_type = 0;
  61     a[0].a_val = 0;
  62
  63     fd = open("/proc/self/auxv", O_RDONLY);
  64     if (fd < 0) {
  65         return a;
  66     }
  67
  68     /* Read the first SIZE bytes.  Hopefully, this covers everything.  */
  69     r = read(fd, a, size);
  70
  71     if (r == size) {
  72         /* Continue to expand until we do get a partial read.  */
  73         do {
  74             ofs = size;
  75             size *= 2;
  76             auxv = a = g_realloc(a, size);
  77             r = read(fd, (char *)a + ofs, ofs);
  78         } while (r == ofs);
  79     }
  80
  81     close(fd);
  82     return a;
  83 }
  84
  85 unsigned long qemu_getauxval(unsigned long type)
  86 {
  87     const ElfW_auxv_t *a = auxv;
  88
  89     if (unlikely(a == NULL)) {
  90         a = qemu_init_auxval();
  91     }
  92
  93     for (; a->a_type != 0; a++) {
  94         if (a->a_type == type) {
  95             return a->a_val;
  96         }
  97     }
  98
  99     return 0;
 100 }
 101
 102 #else
 103
 104 unsigned long qemu_getauxval(unsigned long type)
 105 {
 106     return 0;
 107 }
 108
 109 #endif