elf/dl-hwcaps.c

   1 /* Hardware capability support for run-time dynamic loader.
   2    Copyright (C) 2012 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    <http://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
  28 #ifdef _DL_FIRST_PLATFORM
  29 # define _DL_FIRST_EXTRA (_DL_FIRST_PLATFORM + _DL_PLATFORMS_COUNT)
  30 #else
  31 # define _DL_FIRST_EXTRA _DL_HWCAP_COUNT
  32 #endif
  33
  34 /* Return an array of useful/necessary hardware capability names.  */
  35 const struct r_strlenpair *
  36 internal_function
  37 _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
  38                       size_t *max_capstrlen)
  39 {
  40   /* Determine how many important bits are set.  */
  41   uint64_t masked = GLRO(dl_hwcap) & GLRO(dl_hwcap_mask);
  42   size_t cnt = platform != NULL;
  43   size_t n, m;
  44   size_t total;
  45   struct r_strlenpair *temp;
  46   struct r_strlenpair *result;
  47   struct r_strlenpair *rp;
  48   char *cp;
  49
  50   /* Count the number of bits set in the masked value.  */
  51   for (n = 0; (~((1ULL << n) - 1) & masked) != 0; ++n)
  52     if ((masked & (1ULL << n)) != 0)
  53       ++cnt;
  54
  55 #if defined NEED_DL_SYSINFO || defined NEED_DL_SYSINFO_DSO
  56   /* The system-supplied DSO can contain a note of type 2, vendor "GNU".
  57      This gives us a list of names to treat as fake hwcap bits.  */
  58
  59   const char *dsocaps = NULL;
  60   size_t dsocapslen = 0;
  61   if (GLRO(dl_sysinfo_map) != NULL)
  62     {
  63       const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
  64       const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
  65       for (uint_fast16_t i = 0; i < phnum; ++i)
  66         if (phdr[i].p_type == PT_NOTE)
  67           {
  68             const ElfW(Addr) start = (phdr[i].p_vaddr
  69                                       + GLRO(dl_sysinfo_map)->l_addr);
  70             const struct
  71             {
  72               ElfW(Word) vendorlen;
  73               ElfW(Word) datalen;
  74               ElfW(Word) type;
  75             } *note = (const void *) start;
  76             while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
  77               {
  78 #define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word)))
  79                 if (note->type == NT_GNU_HWCAP
  80                     && note->vendorlen == sizeof "GNU"
  81                     && !memcmp ((note + 1), "GNU", sizeof "GNU")
  82                     && note->datalen > 2 * sizeof (ElfW(Word)) + 2)
  83                   {
  84                     const ElfW(Word) *p = ((const void *) (note + 1)
  85                                            + ROUND (sizeof "GNU"));
  86                     cnt += *p++;
  87                     ++p;        /* Skip mask word.  */
  88                     dsocaps = (const char *) p;
  89                     dsocapslen = note->datalen - sizeof *p * 2;
  90                     break;
  91                   }
  92                 note = ((const void *) (note + 1)
  93                         + ROUND (note->vendorlen) + ROUND (note->datalen));
  94 #undef ROUND
  95               }
  96             if (dsocaps != NULL)
  97               break;
  98           }
  99     }
 100 #endif
 101
 102   /* For TLS enabled builds always add 'tls'.  */
 103   ++cnt;
 104
 105   /* Create temporary data structure to generate result table.  */
 106   temp = (struct r_strlenpair *) alloca (cnt * sizeof (*temp));
 107   m = 0;
 108 #if defined NEED_DL_SYSINFO || defined NEED_DL_SYSINFO_DSO
 109   if (dsocaps != NULL)
 110     {
 111       const ElfW(Word) mask = ((const ElfW(Word) *) dsocaps)[-1];
 112       GLRO(dl_hwcap) |= (uint64_t) mask << _DL_FIRST_EXTRA;
 113       /* Note that we add the dsocaps to the set already chosen by the
 114          LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).
 115          So there is no way to request ignoring an OS-supplied dsocap
 116          string and bit like you can ignore an OS-supplied HWCAP bit.  */
 117       GLRO(dl_hwcap_mask) |= (uint64_t) mask << _DL_FIRST_EXTRA;
 118       size_t len;
 119       for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)
 120         {
 121           uint_fast8_t bit = *p++;
 122           len = strlen (p);
 123
 124           /* Skip entries that are not enabled in the mask word.  */
 125           if (__builtin_expect (mask & ((ElfW(Word)) 1 << bit), 1))
 126             {
 127               temp[m].str = p;
 128               temp[m].len = len;
 129               ++m;
 130             }
 131           else
 132             --cnt;
 133         }
 134     }
 135 #endif
 136   for (n = 0; masked != 0; ++n)
 137     if ((masked & (1ULL << n)) != 0)
 138       {
 139         temp[m].str = _dl_hwcap_string (n);
 140         temp[m].len = strlen (temp[m].str);
 141         masked ^= 1ULL << n;
 142         ++m;
 143       }
 144   if (platform != NULL)
 145     {
 146       temp[m].str = platform;
 147       temp[m].len = platform_len;
 148       ++m;
 149     }
 150
 151   temp[m].str = "tls";
 152   temp[m].len = 3;
 153   ++m;
 154
 155   assert (m == cnt);
 156
 157   /* Determine the total size of all strings together.  */
 158   if (cnt == 1)
 159     total = temp[0].len + 1;
 160   else
 161     {
 162       total = temp[0].len + temp[cnt - 1].len + 2;
 163       if (cnt > 2)
 164         {
 165           total <<= 1;
 166           for (n = 1; n + 1 < cnt; ++n)
 167             total += temp[n].len + 1;
 168           if (cnt > 3
 169               && (cnt >= sizeof (size_t) * 8
 170                   || total + (sizeof (*result) << 3)
 171                      >= (1UL << (sizeof (size_t) * 8 - cnt + 3))))
 172             _dl_signal_error (ENOMEM, NULL, NULL,
 173                               N_("cannot create capability list"));
 174
 175           total <<= cnt - 3;
 176         }
 177     }
 178
 179   /* The result structure: we use a very compressed way to store the
 180      various combinations of capability names.  */
 181   *sz = 1 << cnt;
 182   result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);
 183   if (result == NULL)
 184     _dl_signal_error (ENOMEM, NULL, NULL,
 185                       N_("cannot create capability list"));
 186
 187   if (cnt == 1)
 188     {
 189       result[0].str = (char *) (result + *sz);
 190       result[0].len = temp[0].len + 1;
 191       result[1].str = (char *) (result + *sz);
 192       result[1].len = 0;
 193       cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);
 194       *cp = '/';
 195       *sz = 2;
 196       *max_capstrlen = result[0].len;
 197
 198       return result;
 199     }
 200
 201   /* Fill in the information.  This follows the following scheme
 202      (indeces from TEMP for four strings):
 203         entry #0: 0, 1, 2, 3    binary: 1111
 204               #1: 0, 1, 3               1101
 205               #2: 0, 2, 3               1011
 206               #3: 0, 3                  1001
 207      This allows the representation of all possible combinations of
 208      capability names in the string.  First generate the strings.  */
 209   result[1].str = result[0].str = cp = (char *) (result + *sz);
 210 #define add(idx) \
 211       cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);
 212   if (cnt == 2)
 213     {
 214       add (1);
 215       add (0);
 216     }
 217   else
 218     {
 219       n = 1 << (cnt - 1);
 220       do
 221         {
 222           n -= 2;
 223
 224           /* We always add the last string.  */
 225           add (cnt - 1);
 226
 227           /* Add the strings which have the bit set in N.  */
 228           for (m = cnt - 2; m > 0; --m)
 229             if ((n & (1 << m)) != 0)
 230               add (m);
 231
 232           /* Always add the first string.  */
 233           add (0);
 234         }
 235       while (n != 0);
 236     }
 237 #undef add
 238
 239   /* Now we are ready to install the string pointers and length.  */
 240   for (n = 0; n < (1UL << cnt); ++n)
 241     result[n].len = 0;
 242   n = cnt;
 243   do
 244     {
 245       size_t mask = 1 << --n;
 246
 247       rp = result;
 248       for (m = 1 << cnt; m > 0; ++rp)
 249         if ((--m & mask) != 0)
 250           rp->len += temp[n].len + 1;
 251     }
 252   while (n != 0);
 253
 254   /* The first half of the strings all include the first string.  */
 255   n = (1 << cnt) - 2;
 256   rp = &result[2];
 257   while (n != (1UL << (cnt - 1)))
 258     {
 259       if ((--n & 1) != 0)
 260         rp[0].str = rp[-2].str + rp[-2].len;
 261       else
 262         rp[0].str = rp[-1].str;
 263       ++rp;
 264     }
 265
 266   /* The second half starts right after the first part of the string of
 267      the corresponding entry in the first half.  */
 268   do
 269     {
 270       rp[0].str = rp[-(1 << (cnt - 1))].str + temp[cnt - 1].len + 1;
 271       ++rp;
 272     }
 273   while (--n != 0);
 274
 275   /* The maximum string length.  */
 276   *max_capstrlen = result[0].len;
 277
 278   return result;
 279 }