elf/dl-hwcaps.c

   1 /* Hardware capability support for run-time dynamic loader.
   2    Copyright (C) 2012-2020 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <elf.h>
  21 #include <errno.h>
  22 #include <libintl.h>
  23 #include <unistd.h>
  24 #include <ldsodefs.h>
  25
  26 #include <dl-procinfo.h>
  27 #include <dl-hwcaps.h>
  28
  29 /* Return an array of useful/necessary hardware capability names.  */
  30 const struct r_strlenpair *
  31 _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
  32                       size_t *max_capstrlen)
  33 {
  34   uint64_t hwcap_mask = GET_HWCAP_MASK();
  35   /* Determine how many important bits are set.  */
  36   uint64_t masked = GLRO(dl_hwcap) & hwcap_mask;
  37   size_t cnt = platform != NULL;
  38   size_t n, m;
  39   size_t total;
  40   struct r_strlenpair *result;
  41   struct r_strlenpair *rp;
  42   char *cp;
  43
  44   /* Count the number of bits set in the masked value.  */
  45   for (n = 0; (~((1ULL << n) - 1) & masked) != 0; ++n)
  46     if ((masked & (1ULL << n)) != 0)
  47       ++cnt;
  48
  49   /* For TLS enabled builds always add 'tls'.  */
  50   ++cnt;
  51
  52   /* Create temporary data structure to generate result table.  */
  53   struct r_strlenpair temp[cnt];
  54   m = 0;
  55   for (n = 0; masked != 0; ++n)
  56     if ((masked & (1ULL << n)) != 0)
  57       {
  58         temp[m].str = _dl_hwcap_string (n);
  59         temp[m].len = strlen (temp[m].str);
  60         masked ^= 1ULL << n;
  61         ++m;
  62       }
  63   if (platform != NULL)
  64     {
  65       temp[m].str = platform;
  66       temp[m].len = platform_len;
  67       ++m;
  68     }
  69
  70   temp[m].str = "tls";
  71   temp[m].len = 3;
  72   ++m;
  73
  74   assert (m == cnt);
  75
  76   /* Determine the total size of all strings together.  */
  77   if (cnt == 1)
  78     total = temp[0].len + 1;
  79   else
  80     {
  81       total = temp[0].len + temp[cnt - 1].len + 2;
  82       if (cnt > 2)
  83         {
  84           total <<= 1;
  85           for (n = 1; n + 1 < cnt; ++n)
  86             total += temp[n].len + 1;
  87           if (cnt > 3
  88               && (cnt >= sizeof (size_t) * 8
  89                   || total + (sizeof (*result) << 3)
  90                      >= (1UL << (sizeof (size_t) * 8 - cnt + 3))))
  91             _dl_signal_error (ENOMEM, NULL, NULL,
  92                               N_("cannot create capability list"));
  93
  94           total <<= cnt - 3;
  95         }
  96     }
  97
  98   /* The result structure: we use a very compressed way to store the
  99      various combinations of capability names.  */
 100   *sz = 1 << cnt;
 101   result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);
 102   if (result == NULL)
 103     _dl_signal_error (ENOMEM, NULL, NULL,
 104                       N_("cannot create capability list"));
 105
 106   if (cnt == 1)
 107     {
 108       result[0].str = (char *) (result + *sz);
 109       result[0].len = temp[0].len + 1;
 110       result[1].str = (char *) (result + *sz);
 111       result[1].len = 0;
 112       cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);
 113       *cp = '/';
 114       *sz = 2;
 115       *max_capstrlen = result[0].len;
 116
 117       return result;
 118     }
 119
 120   /* Fill in the information.  This follows the following scheme
 121      (indices from TEMP for four strings):
 122         entry #0: 0, 1, 2, 3    binary: 1111
 123               #1: 0, 1, 3               1101
 124               #2: 0, 2, 3               1011
 125               #3: 0, 3                  1001
 126      This allows the representation of all possible combinations of
 127      capability names in the string.  First generate the strings.  */
 128   result[1].str = result[0].str = cp = (char *) (result + *sz);
 129 #define add(idx) \
 130       cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);
 131   if (cnt == 2)
 132     {
 133       add (1);
 134       add (0);
 135     }
 136   else
 137     {
 138       n = 1 << (cnt - 1);
 139       do
 140         {
 141           n -= 2;
 142
 143           /* We always add the last string.  */
 144           add (cnt - 1);
 145
 146           /* Add the strings which have the bit set in N.  */
 147           for (m = cnt - 2; m > 0; --m)
 148             if ((n & (1 << m)) != 0)
 149               add (m);
 150
 151           /* Always add the first string.  */
 152           add (0);
 153         }
 154       while (n != 0);
 155     }
 156 #undef add
 157
 158   /* Now we are ready to install the string pointers and length.  */
 159   for (n = 0; n < (1UL << cnt); ++n)
 160     result[n].len = 0;
 161   n = cnt;
 162   do
 163     {
 164       size_t mask = 1 << --n;
 165
 166       rp = result;
 167       for (m = 1 << cnt; m > 0; ++rp)
 168         if ((--m & mask) != 0)
 169           rp->len += temp[n].len + 1;
 170     }
 171   while (n != 0);
 172
 173   /* The first half of the strings all include the first string.  */
 174   n = (1 << cnt) - 2;
 175   rp = &result[2];
 176   while (n != (1UL << (cnt - 1)))
 177     {
 178       if ((--n & 1) != 0)
 179         rp[0].str = rp[-2].str + rp[-2].len;
 180       else
 181         rp[0].str = rp[-1].str;
 182       ++rp;
 183     }
 184
 185   /* The second half starts right after the first part of the string of
 186      the corresponding entry in the first half.  */
 187   do
 188     {
 189       rp[0].str = rp[-(1 << (cnt - 1))].str + temp[cnt - 1].len + 1;
 190       ++rp;
 191     }
 192   while (--n != 0);
 193
 194   /* The maximum string length.  */
 195   *max_capstrlen = result[0].len;
 196
 197   return result;
 198 }