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