elf/dl-hwcaps.c

   1 /* Hardware capability support for run-time dynamic loader.
   2    Copyright (C) 2012-2018 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             /* NB: Some PT_NOTE segment may have alignment value of 0
  71                or 1.  gABI specifies that PT_NOTE segments should be
  72                aligned to 4 bytes in 32-bit objects and to 8 bytes in
  73                64-bit objects.  As a Linux extension, we also support
  74                4 byte alignment in 64-bit objects.  If p_align is less
  75                than 4, we treate alignment as 4 bytes since some note
  76                segments have 0 or 1 byte alignment.   */
  77             ElfW(Addr) align = phdr[i].p_align;
  78             if (align < 4)
  79               align = 4;
  80             else if (align != 4 && align != 8)
  81               continue;
  82             /* The standard ELF note layout is exactly as the anonymous struct.
  83                The next element is a variable length vendor name of length
  84                VENDORLEN (with a real length rounded to ElfW(Word)), followed
  85                by the data of length DATALEN (with a real length rounded to
  86                ElfW(Word)).  */
  87             const struct
  88             {
  89               ElfW(Word) vendorlen;
  90               ElfW(Word) datalen;
  91               ElfW(Word) type;
  92             } *note = (const void *) start;
  93             while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
  94               {
  95                 /* The layout of the type 2, vendor "GNU" note is as follows:
  96                    .long <Number of capabilities enabled by this note>
  97                    .long <Capabilities mask> (as mask >> _DL_FIRST_EXTRA).
  98                    .byte <The bit number for the next capability>
  99                    .asciz <The name of the capability>.  */
 100                 if (note->type == NT_GNU_HWCAP
 101                     && note->vendorlen == sizeof "GNU"
 102                     && !memcmp ((note + 1), "GNU", sizeof "GNU")
 103                     && note->datalen > 2 * sizeof (ElfW(Word)) + 2)
 104                   {
 105                     const ElfW(Word) *p
 106                       = ((const void *) note
 107                          + ELF_NOTE_DESC_OFFSET (sizeof "GNU", align));
 108                     cnt += *p++;
 109                     ++p;        /* Skip mask word.  */
 110                     dsocaps = (const char *) p; /* Pseudo-string "<b>name"  */
 111                     dsocapslen = note->datalen - sizeof *p * 2;
 112                     break;
 113                   }
 114                 note = ((const void *) note
 115                         + ELF_NOTE_NEXT_OFFSET (note->vendorlen,
 116                                                 note->datalen, align));
 117               }
 118             if (dsocaps != NULL)
 119               break;
 120           }
 121     }
 122 #endif
 123
 124   /* For TLS enabled builds always add 'tls'.  */
 125   ++cnt;
 126
 127   /* Create temporary data structure to generate result table.  */
 128   struct r_strlenpair temp[cnt];
 129   m = 0;
 130 #ifdef NEED_DL_SYSINFO_DSO
 131   if (dsocaps != NULL)
 132     {
 133       /* dsocaps points to the .asciz string, and -1 points to the mask
 134          .long just before the string.  */
 135       const ElfW(Word) mask = ((const ElfW(Word) *) dsocaps)[-1];
 136       GLRO(dl_hwcap) |= (uint64_t) mask << _DL_FIRST_EXTRA;
 137       /* Note that we add the dsocaps to the set already chosen by the
 138          LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).
 139          So there is no way to request ignoring an OS-supplied dsocap
 140          string and bit like you can ignore an OS-supplied HWCAP bit.  */
 141       hwcap_mask |= (uint64_t) mask << _DL_FIRST_EXTRA;
 142 #if HAVE_TUNABLES
 143       TUNABLE_SET (glibc, tune, hwcap_mask, uint64_t, hwcap_mask);
 144 #else
 145       GLRO(dl_hwcap_mask) = hwcap_mask;
 146 #endif
 147       size_t len;
 148       for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)
 149         {
 150           uint_fast8_t bit = *p++;
 151           len = strlen (p);
 152
 153           /* Skip entries that are not enabled in the mask word.  */
 154           if (__glibc_likely (mask & ((ElfW(Word)) 1 << bit)))
 155             {
 156               temp[m].str = p;
 157               temp[m].len = len;
 158               ++m;
 159             }
 160           else
 161             --cnt;
 162         }
 163     }
 164 #endif
 165   for (n = 0; masked != 0; ++n)
 166     if ((masked & (1ULL << n)) != 0)
 167       {
 168         temp[m].str = _dl_hwcap_string (n);
 169         temp[m].len = strlen (temp[m].str);
 170         masked ^= 1ULL << n;
 171         ++m;
 172       }
 173   if (platform != NULL)
 174     {
 175       temp[m].str = platform;
 176       temp[m].len = platform_len;
 177       ++m;
 178     }
 179
 180   temp[m].str = "tls";
 181   temp[m].len = 3;
 182   ++m;
 183
 184   assert (m == cnt);
 185
 186   /* Determine the total size of all strings together.  */
 187   if (cnt == 1)
 188     total = temp[0].len + 1;
 189   else
 190     {
 191       total = temp[0].len + temp[cnt - 1].len + 2;
 192       if (cnt > 2)
 193         {
 194           total <<= 1;
 195           for (n = 1; n + 1 < cnt; ++n)
 196             total += temp[n].len + 1;
 197           if (cnt > 3
 198               && (cnt >= sizeof (size_t) * 8
 199                   || total + (sizeof (*result) << 3)
 200                      >= (1UL << (sizeof (size_t) * 8 - cnt + 3))))
 201             _dl_signal_error (ENOMEM, NULL, NULL,
 202                               N_("cannot create capability list"));
 203
 204           total <<= cnt - 3;
 205         }
 206     }
 207
 208   /* The result structure: we use a very compressed way to store the
 209      various combinations of capability names.  */
 210   *sz = 1 << cnt;
 211   result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);
 212   if (result == NULL)
 213     _dl_signal_error (ENOMEM, NULL, NULL,
 214                       N_("cannot create capability list"));
 215
 216   if (cnt == 1)
 217     {
 218       result[0].str = (char *) (result + *sz);
 219       result[0].len = temp[0].len + 1;
 220       result[1].str = (char *) (result + *sz);
 221       result[1].len = 0;
 222       cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);
 223       *cp = '/';
 224       *sz = 2;
 225       *max_capstrlen = result[0].len;
 226
 227       return result;
 228     }
 229
 230   /* Fill in the information.  This follows the following scheme
 231      (indices from TEMP for four strings):
 232         entry #0: 0, 1, 2, 3    binary: 1111
 233               #1: 0, 1, 3               1101
 234               #2: 0, 2, 3               1011
 235               #3: 0, 3                  1001
 236      This allows the representation of all possible combinations of
 237      capability names in the string.  First generate the strings.  */
 238   result[1].str = result[0].str = cp = (char *) (result + *sz);
 239 #define add(idx) \
 240       cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);
 241   if (cnt == 2)
 242     {
 243       add (1);
 244       add (0);
 245     }
 246   else
 247     {
 248       n = 1 << (cnt - 1);
 249       do
 250         {
 251           n -= 2;
 252
 253           /* We always add the last string.  */
 254           add (cnt - 1);
 255
 256           /* Add the strings which have the bit set in N.  */
 257           for (m = cnt - 2; m > 0; --m)
 258             if ((n & (1 << m)) != 0)
 259               add (m);
 260
 261           /* Always add the first string.  */
 262           add (0);
 263         }
 264       while (n != 0);
 265     }
 266 #undef add
 267
 268   /* Now we are ready to install the string pointers and length.  */
 269   for (n = 0; n < (1UL << cnt); ++n)
 270     result[n].len = 0;
 271   n = cnt;
 272   do
 273     {
 274       size_t mask = 1 << --n;
 275
 276       rp = result;
 277       for (m = 1 << cnt; m > 0; ++rp)
 278         if ((--m & mask) != 0)
 279           rp->len += temp[n].len + 1;
 280     }
 281   while (n != 0);
 282
 283   /* The first half of the strings all include the first string.  */
 284   n = (1 << cnt) - 2;
 285   rp = &result[2];
 286   while (n != (1UL << (cnt - 1)))
 287     {
 288       if ((--n & 1) != 0)
 289         rp[0].str = rp[-2].str + rp[-2].len;
 290       else
 291         rp[0].str = rp[-1].str;
 292       ++rp;
 293     }
 294
 295   /* The second half starts right after the first part of the string of
 296      the corresponding entry in the first half.  */
 297   do
 298     {
 299       rp[0].str = rp[-(1 << (cnt - 1))].str + temp[cnt - 1].len + 1;
 300       ++rp;
 301     }
 302   while (--n != 0);
 303
 304   /* The maximum string length.  */
 305   *max_capstrlen = result[0].len;
 306
 307   return result;
 308 }