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/osdep.h"
  26
  27 #ifdef CONFIG_GETAUXVAL
  28 /* Don't inline this in qemu/osdep.h, because pulling in <sys/auxv.h> for
  29    the system declaration of getauxval pulls in the system <elf.h>, which
  30    conflicts with qemu's version.  */
  31
  32 #include <sys/auxv.h>
  33
  34 unsigned long qemu_getauxval(unsigned long key)
  35 {
  36     return getauxval(key);
  37 }
  38 #elif defined(__linux__)
  39 #include "elf.h"
  40
  41 /* Our elf.h doesn't contain Elf32_auxv_t and Elf64_auxv_t, which is ok because
  42    that just makes it easier to define it properly for the host here.  */
  43 typedef struct {
  44     unsigned long a_type;
  45     unsigned long a_val;
  46 } ElfW_auxv_t;
  47
  48 static const ElfW_auxv_t *auxv;
  49
  50 static const ElfW_auxv_t *qemu_init_auxval(void)
  51 {
  52     ElfW_auxv_t *a;
  53     ssize_t size = 512, r, ofs;
  54     int fd;
  55
  56     /* Allocate some initial storage.  Make sure the first entry is set
  57        to end-of-list, so that we've got a valid list in case of error.  */
  58     auxv = a = g_malloc(size);
  59     a[0].a_type = 0;
  60     a[0].a_val = 0;
  61
  62     fd = open("/proc/self/auxv", O_RDONLY);
  63     if (fd < 0) {
  64         return a;
  65     }
  66
  67     /* Read the first SIZE bytes.  Hopefully, this covers everything.  */
  68     r = read(fd, a, size);
  69
  70     if (r == size) {
  71         /* Continue to expand until we do get a partial read.  */
  72         do {
  73             ofs = size;
  74             size *= 2;
  75             auxv = a = g_realloc(a, size);
  76             r = read(fd, (char *)a + ofs, ofs);
  77         } while (r == ofs);
  78     }
  79
  80     close(fd);
  81     return a;
  82 }
  83
  84 unsigned long qemu_getauxval(unsigned long type)
  85 {
  86     const ElfW_auxv_t *a = auxv;
  87
  88     if (unlikely(a == NULL)) {
  89         a = qemu_init_auxval();
  90     }
  91
  92     for (; a->a_type != 0; a++) {
  93         if (a->a_type == type) {
  94             return a->a_val;
  95         }
  96     }
  97
  98     return 0;
  99 }
 100
 101 #else
 102
 103 unsigned long qemu_getauxval(unsigned long type)
 104 {
 105     return 0;
 106 }
 107
 108 #endif