elf/dl-hwcaps.c

   1 /* Hardware capability support for run-time dynamic loader.
   2    Copyright (C) 2012-2013 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 *result;
  46   struct r_strlenpair *rp;
  47   char *cp;
  48
  49   /* Count the number of bits set in the masked value.  */
  50   for (n = 0; (~((1ULL << n) - 1) & masked) != 0; ++n)
  51     if ((masked & (1ULL << n)) != 0)
  52       ++cnt;
  53
  54 #ifdef NEED_DL_SYSINFO_DSO
  55   /* The system-supplied DSO can contain a note of type 2, vendor "GNU".
  56      This gives us a list of names to treat as fake hwcap bits.  */
  57
  58   const char *dsocaps = NULL;
  59   size_t dsocapslen = 0;
  60   if (GLRO(dl_sysinfo_map) != NULL)
  61     {
  62       const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
  63       const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
  64       for (uint_fast16_t i = 0; i < phnum; ++i)
  65         if (phdr[i].p_type == PT_NOTE)
  66           {
  67             const ElfW(Addr) start = (phdr[i].p_vaddr
  68                                       + GLRO(dl_sysinfo_map)->l_addr);
  69             const struct
  70             {
  71               ElfW(Word) vendorlen;
  72               ElfW(Word) datalen;
  73               ElfW(Word) type;
  74             } *note = (const void *) start;
  75             while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
  76               {
  77 #define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word)))
  78                 if (note->type == NT_GNU_HWCAP
  79                     && note->vendorlen == sizeof "GNU"
  80                     && !memcmp ((note + 1), "GNU", sizeof "GNU")
  81                     && note->datalen > 2 * sizeof (ElfW(Word)) + 2)
  82                   {
  83                     const ElfW(Word) *p = ((const void *) (note + 1)
  84                                            + ROUND (sizeof "GNU"));
  85                     cnt += *p++;
  86                     ++p;        /* Skip mask word.  */
  87                     dsocaps = (const char *) p;
  88                     dsocapslen = note->datalen - sizeof *p * 2;
  89                     break;
  90                   }
  91                 note = ((const void *) (note + 1)
  92                         + ROUND (note->vendorlen) + ROUND (note->datalen));
  93 #undef ROUND
  94               }
  95             if (dsocaps != NULL)
  96               break;
  97           }
  98     }
  99 #endif
 100
 101   /* For TLS enabled builds always add 'tls'.  */
 102   ++cnt;
 103
 104   /* Create temporary data structure to generate result table.  */
 105   struct r_strlenpair temp[cnt];
 106   m = 0;
 107 #ifdef NEED_DL_SYSINFO_DSO
 108   if (dsocaps != NULL)
 109     {
 110       const ElfW(Word) mask = ((const ElfW(Word) *) dsocaps)[-1];
 111       GLRO(dl_hwcap) |= (uint64_t) mask << _DL_FIRST_EXTRA;
 112       /* Note that we add the dsocaps to the set already chosen by the
 113          LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).
 114          So there is no way to request ignoring an OS-supplied dsocap
 115          string and bit like you can ignore an OS-supplied HWCAP bit.  */
 116       GLRO(dl_hwcap_mask) |= (uint64_t) mask << _DL_FIRST_EXTRA;
 117       size_t len;
 118       for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)
 119         {
 120           uint_fast8_t bit = *p++;
 121           len = strlen (p);
 122
 123           /* Skip entries that are not enabled in the mask word.  */
 124           if (__builtin_expect (mask & ((ElfW(Word)) 1 << bit), 1))
 125             {
 126               temp[m].str = p;
 127               temp[m].len = len;
 128               ++m;
 129             }
 130           else
 131             --cnt;
 132         }
 133     }
 134 #endif
 135   for (n = 0; masked != 0; ++n)
 136     if ((masked & (1ULL << n)) != 0)
 137       {
 138         temp[m].str = _dl_hwcap_string (n);
 139         temp[m].len = strlen (temp[m].str);
 140         masked ^= 1ULL << n;
 141         ++m;
 142       }
 143   if (platform != NULL)
 144     {
 145       temp[m].str = platform;
 146       temp[m].len = platform_len;
 147       ++m;
 148     }
 149
 150   temp[m].str = "tls";
 151   temp[m].len = 3;
 152   ++m;
 153
 154   assert (m == cnt);
 155
 156   /* Determine the total size of all strings together.  */
 157   if (cnt == 1)
 158     total = temp[0].len + 1;
 159   else
 160     {
 161       total = temp[0].len + temp[cnt - 1].len + 2;
 162       if (cnt > 2)
 163         {
 164           total <<= 1;
 165           for (n = 1; n + 1 < cnt; ++n)
 166             total += temp[n].len + 1;
 167           if (cnt > 3
 168               && (cnt >= sizeof (size_t) * 8
 169                   || total + (sizeof (*result) << 3)
 170                      >= (1UL << (sizeof (size_t) * 8 - cnt + 3))))
 171             _dl_signal_error (ENOMEM, NULL, NULL,
 172                               N_("cannot create capability list"));
 173
 174           total <<= cnt - 3;
 175         }
 176     }
 177
 178   /* The result structure: we use a very compressed way to store the
 179      various combinations of capability names.  */
 180   *sz = 1 << cnt;
 181   result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);
 182   if (result == NULL)
 183     _dl_signal_error (ENOMEM, NULL, NULL,
 184                       N_("cannot create capability list"));
 185
 186   if (cnt == 1)
 187     {
 188       result[0].str = (char *) (result + *sz);
 189       result[0].len = temp[0].len + 1;
 190       result[1].str = (char *) (result + *sz);
 191       result[1].len = 0;
 192       cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);
 193       *cp = '/';
 194       *sz = 2;
 195       *max_capstrlen = result[0].len;
 196
 197       return result;
 198     }
 199
 200   /* Fill in the information.  This follows the following scheme
 201      (indices from TEMP for four strings):
 202         entry #0: 0, 1, 2, 3    binary: 1111
 203               #1: 0, 1, 3               1101
 204               #2: 0, 2, 3               1011
 205               #3: 0, 3                  1001
 206      This allows the representation of all possible combinations of
 207      capability names in the string.  First generate the strings.  */
 208   result[1].str = result[0].str = cp = (char *) (result + *sz);
 209 #define add(idx) \
 210       cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);
 211   if (cnt == 2)
 212     {
 213       add (1);
 214       add (0);
 215     }
 216   else
 217     {
 218       n = 1 << (cnt - 1);
 219       do
 220         {
 221           n -= 2;
 222
 223           /* We always add the last string.  */
 224           add (cnt - 1);
 225
 226           /* Add the strings which have the bit set in N.  */
 227           for (m = cnt - 2; m > 0; --m)
 228             if ((n & (1 << m)) != 0)
 229               add (m);
 230
 231           /* Always add the first string.  */
 232           add (0);
 233         }
 234       while (n != 0);
 235     }
 236 #undef add
 237
 238   /* Now we are ready to install the string pointers and length.  */
 239   for (n = 0; n < (1UL << cnt); ++n)
 240     result[n].len = 0;
 241   n = cnt;
 242   do
 243     {
 244       size_t mask = 1 << --n;
 245
 246       rp = result;
 247       for (m = 1 << cnt; m > 0; ++rp)
 248         if ((--m & mask) != 0)
 249           rp->len += temp[n].len + 1;
 250     }
 251   while (n != 0);
 252
 253   /* The first half of the strings all include the first string.  */
 254   n = (1 << cnt) - 2;
 255   rp = &result[2];
 256   while (n != (1UL << (cnt - 1)))
 257     {
 258       if ((--n & 1) != 0)
 259         rp[0].str = rp[-2].str + rp[-2].len;
 260       else
 261         rp[0].str = rp[-1].str;
 262       ++rp;
 263     }
 264
 265   /* The second half starts right after the first part of the string of
 266      the corresponding entry in the first half.  */
 267   do
 268     {
 269       rp[0].str = rp[-(1 << (cnt - 1))].str + temp[cnt - 1].len + 1;
 270       ++rp;
 271     }
 272   while (--n != 0);
 273
 274   /* The maximum string length.  */
 275   *max_capstrlen = result[0].len;
 276
 277   return result;
 278 }