elf/dl-hwcaps.c

   1 /* Hardware capability support for run-time dynamic loader.
   2    Copyright (C) 2012-2017 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 #include <dl-hwcaps.h>
  28
  29 #ifdef _DL_FIRST_PLATFORM
  30 # define _DL_FIRST_EXTRA (_DL_FIRST_PLATFORM + _DL_PLATFORMS_COUNT)
  31 #else
  32 # define _DL_FIRST_EXTRA _DL_HWCAP_COUNT
  33 #endif
  34
  35 /* Return an array of useful/necessary hardware capability names.  */
  36 const struct r_strlenpair *
  37 _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
  38                       size_t *max_capstrlen)
  39 {
  40   uint64_t hwcap_mask = GET_HWCAP_MASK();
  41   /* Determine how many important bits are set.  */
  42   uint64_t masked = GLRO(dl_hwcap) & hwcap_mask;
  43   size_t cnt = platform != NULL;
  44   size_t n, m;
  45   size_t total;
  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 #ifdef 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             /* The standard ELF note layout is exactly as the anonymous struct.
  71                The next element is a variable length vendor name of length
  72                VENDORLEN (with a real length rounded to ElfW(Word)), followed
  73                by the data of length DATALEN (with a real length rounded to
  74                ElfW(Word)).  */
  75             const struct
  76             {
  77               ElfW(Word) vendorlen;
  78               ElfW(Word) datalen;
  79               ElfW(Word) type;
  80             } *note = (const void *) start;
  81             while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
  82               {
  83 #define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word)))
  84                 /* The layout of the type 2, vendor "GNU" note is as follows:
  85                    .long <Number of capabilities enabled by this note>
  86                    .long <Capabilities mask> (as mask >> _DL_FIRST_EXTRA).
  87                    .byte <The bit number for the next capability>
  88                    .asciz <The name of the capability>.  */
  89                 if (note->type == NT_GNU_HWCAP
  90                     && note->vendorlen == sizeof "GNU"
  91                     && !memcmp ((note + 1), "GNU", sizeof "GNU")
  92                     && note->datalen > 2 * sizeof (ElfW(Word)) + 2)
  93                   {
  94                     const ElfW(Word) *p = ((const void *) (note + 1)
  95                                            + ROUND (sizeof "GNU"));
  96                     cnt += *p++;
  97                     ++p;        /* Skip mask word.  */
  98                     dsocaps = (const char *) p; /* Pseudo-string "<b>name"  */
  99                     dsocapslen = note->datalen - sizeof *p * 2;
 100                     break;
 101                   }
 102                 note = ((const void *) (note + 1)
 103                         + ROUND (note->vendorlen) + ROUND (note->datalen));
 104 #undef ROUND
 105               }
 106             if (dsocaps != NULL)
 107               break;
 108           }
 109     }
 110 #endif
 111
 112   /* For TLS enabled builds always add 'tls'.  */
 113   ++cnt;
 114
 115   /* Create temporary data structure to generate result table.  */
 116   struct r_strlenpair temp[cnt];
 117   m = 0;
 118 #ifdef NEED_DL_SYSINFO_DSO
 119   if (dsocaps != NULL)
 120     {
 121       /* dsocaps points to the .asciz string, and -1 points to the mask
 122          .long just before the string.  */
 123       const ElfW(Word) mask = ((const ElfW(Word) *) dsocaps)[-1];
 124       GLRO(dl_hwcap) |= (uint64_t) mask << _DL_FIRST_EXTRA;
 125       /* Note that we add the dsocaps to the set already chosen by the
 126          LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).
 127          So there is no way to request ignoring an OS-supplied dsocap
 128          string and bit like you can ignore an OS-supplied HWCAP bit.  */
 129       hwcap_mask |= (uint64_t) mask << _DL_FIRST_EXTRA;
 130 #if HAVE_TUNABLES
 131       TUNABLE_SET (glibc, tune, hwcap_mask, uint64_t, hwcap_mask);
 132 #else
 133       GLRO(dl_hwcap_mask) = hwcap_mask;
 134 #endif
 135       size_t len;
 136       for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)
 137         {
 138           uint_fast8_t bit = *p++;
 139           len = strlen (p);
 140
 141           /* Skip entries that are not enabled in the mask word.  */
 142           if (__glibc_likely (mask & ((ElfW(Word)) 1 << bit)))
 143             {
 144               temp[m].str = p;
 145               temp[m].len = len;
 146               ++m;
 147             }
 148           else
 149             --cnt;
 150         }
 151     }
 152 #endif
 153   for (n = 0; masked != 0; ++n)
 154     if ((masked & (1ULL << n)) != 0)
 155       {
 156         temp[m].str = _dl_hwcap_string (n);
 157         temp[m].len = strlen (temp[m].str);
 158         masked ^= 1ULL << n;
 159         ++m;
 160       }
 161   if (platform != NULL)
 162     {
 163       temp[m].str = platform;
 164       temp[m].len = platform_len;
 165       ++m;
 166     }
 167
 168   temp[m].str = "tls";
 169   temp[m].len = 3;
 170   ++m;
 171
 172   assert (m == cnt);
 173
 174   /* Determine the total size of all strings together.  */
 175   if (cnt == 1)
 176     total = temp[0].len + 1;
 177   else
 178     {
 179       total = temp[0].len + temp[cnt - 1].len + 2;
 180       if (cnt > 2)
 181         {
 182           total <<= 1;
 183           for (n = 1; n + 1 < cnt; ++n)
 184             total += temp[n].len + 1;
 185           if (cnt > 3
 186               && (cnt >= sizeof (size_t) * 8
 187                   || total + (sizeof (*result) << 3)
 188                      >= (1UL << (sizeof (size_t) * 8 - cnt + 3))))
 189             _dl_signal_error (ENOMEM, NULL, NULL,
 190                               N_("cannot create capability list"));
 191
 192           total <<= cnt - 3;
 193         }
 194     }
 195
 196   /* The result structure: we use a very compressed way to store the
 197      various combinations of capability names.  */
 198   *sz = 1 << cnt;
 199   result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);
 200   if (result == NULL)
 201     _dl_signal_error (ENOMEM, NULL, NULL,
 202                       N_("cannot create capability list"));
 203
 204   if (cnt == 1)
 205     {
 206       result[0].str = (char *) (result + *sz);
 207       result[0].len = temp[0].len + 1;
 208       result[1].str = (char *) (result + *sz);
 209       result[1].len = 0;
 210       cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);
 211       *cp = '/';
 212       *sz = 2;
 213       *max_capstrlen = result[0].len;
 214
 215       return result;
 216     }
 217
 218   /* Fill in the information.  This follows the following scheme
 219      (indices from TEMP for four strings):
 220         entry #0: 0, 1, 2, 3    binary: 1111
 221               #1: 0, 1, 3               1101
 222               #2: 0, 2, 3               1011
 223               #3: 0, 3                  1001
 224      This allows the representation of all possible combinations of
 225      capability names in the string.  First generate the strings.  */
 226   result[1].str = result[0].str = cp = (char *) (result + *sz);
 227 #define add(idx) \
 228       cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);
 229   if (cnt == 2)
 230     {
 231       add (1);
 232       add (0);
 233     }
 234   else
 235     {
 236       n = 1 << (cnt - 1);
 237       do
 238         {
 239           n -= 2;
 240
 241           /* We always add the last string.  */
 242           add (cnt - 1);
 243
 244           /* Add the strings which have the bit set in N.  */
 245           for (m = cnt - 2; m > 0; --m)
 246             if ((n & (1 << m)) != 0)
 247               add (m);
 248
 249           /* Always add the first string.  */
 250           add (0);
 251         }
 252       while (n != 0);
 253     }
 254 #undef add
 255
 256   /* Now we are ready to install the string pointers and length.  */
 257   for (n = 0; n < (1UL << cnt); ++n)
 258     result[n].len = 0;
 259   n = cnt;
 260   do
 261     {
 262       size_t mask = 1 << --n;
 263
 264       rp = result;
 265       for (m = 1 << cnt; m > 0; ++rp)
 266         if ((--m & mask) != 0)
 267           rp->len += temp[n].len + 1;
 268     }
 269   while (n != 0);
 270
 271   /* The first half of the strings all include the first string.  */
 272   n = (1 << cnt) - 2;
 273   rp = &result[2];
 274   while (n != (1UL << (cnt - 1)))
 275     {
 276       if ((--n & 1) != 0)
 277         rp[0].str = rp[-2].str + rp[-2].len;
 278       else
 279         rp[0].str = rp[-1].str;
 280       ++rp;
 281     }
 282
 283   /* The second half starts right after the first part of the string of
 284      the corresponding entry in the first half.  */
 285   do
 286     {
 287       rp[0].str = rp[-(1 << (cnt - 1))].str + temp[cnt - 1].len + 1;
 288       ++rp;
 289     }
 290   while (--n != 0);
 291
 292   /* The maximum string length.  */
 293   *max_capstrlen = result[0].len;
 294
 295   return result;
 296 }