summary refs log tree commit diff
path: root/elf/dl-hwcaps.c
blob: 92f2eb45ce92668882dea921654e219b2e00c71e (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
/* Hardware capability support for run-time dynamic loader.
   Copyright (C) 2012-2017 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <assert.h>
#include <elf.h>
#include <errno.h>
#include <libintl.h>
#include <unistd.h>
#include <ldsodefs.h>

#include <dl-procinfo.h>
#include <dl-hwcaps.h>

#ifdef _DL_FIRST_PLATFORM
# define _DL_FIRST_EXTRA (_DL_FIRST_PLATFORM + _DL_PLATFORMS_COUNT)
#else
# define _DL_FIRST_EXTRA _DL_HWCAP_COUNT
#endif

/* Return an array of useful/necessary hardware capability names.  */
const struct r_strlenpair *
_dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
		      size_t *max_capstrlen)
{
  uint64_t hwcap_mask = GET_HWCAP_MASK();
  /* Determine how many important bits are set.  */
  uint64_t masked = GLRO(dl_hwcap) & hwcap_mask;
  size_t cnt = platform != NULL;
  size_t n, m;
  size_t total;
  struct r_strlenpair *result;
  struct r_strlenpair *rp;
  char *cp;

  /* Count the number of bits set in the masked value.  */
  for (n = 0; (~((1ULL << n) - 1) & masked) != 0; ++n)
    if ((masked & (1ULL << n)) != 0)
      ++cnt;

#ifdef NEED_DL_SYSINFO_DSO
  /* The system-supplied DSO can contain a note of type 2, vendor "GNU".
     This gives us a list of names to treat as fake hwcap bits.  */

  const char *dsocaps = NULL;
  size_t dsocapslen = 0;
  if (GLRO(dl_sysinfo_map) != NULL)
    {
      const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
      const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
      for (uint_fast16_t i = 0; i < phnum; ++i)
	if (phdr[i].p_type == PT_NOTE)
	  {
	    const ElfW(Addr) start = (phdr[i].p_vaddr
				      + GLRO(dl_sysinfo_map)->l_addr);
	    /* The standard ELF note layout is exactly as the anonymous struct.
	       The next element is a variable length vendor name of length
	       VENDORLEN (with a real length rounded to ElfW(Word)), followed
	       by the data of length DATALEN (with a real length rounded to
	       ElfW(Word)).  */
	    const struct
	    {
	      ElfW(Word) vendorlen;
	      ElfW(Word) datalen;
	      ElfW(Word) type;
	    } *note = (const void *) start;
	    while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
	      {
#define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word)))
		/* The layout of the type 2, vendor "GNU" note is as follows:
		   .long <Number of capabilities enabled by this note>
		   .long <Capabilities mask> (as mask >> _DL_FIRST_EXTRA).
		   .byte <The bit number for the next capability>
		   .asciz <The name of the capability>.  */
		if (note->type == NT_GNU_HWCAP
		    && note->vendorlen == sizeof "GNU"
		    && !memcmp ((note + 1), "GNU", sizeof "GNU")
		    && note->datalen > 2 * sizeof (ElfW(Word)) + 2)
		  {
		    const ElfW(Word) *p = ((const void *) (note + 1)
					   + ROUND (sizeof "GNU"));
		    cnt += *p++;
		    ++p;	/* Skip mask word.  */
		    dsocaps = (const char *) p; /* Pseudo-string "<b>name"  */
		    dsocapslen = note->datalen - sizeof *p * 2;
		    break;
		  }
		note = ((const void *) (note + 1)
			+ ROUND (note->vendorlen) + ROUND (note->datalen));
#undef ROUND
	      }
	    if (dsocaps != NULL)
	      break;
	  }
    }
#endif

  /* For TLS enabled builds always add 'tls'.  */
  ++cnt;

  /* Create temporary data structure to generate result table.  */
  struct r_strlenpair temp[cnt];
  m = 0;
#ifdef NEED_DL_SYSINFO_DSO
  if (dsocaps != NULL)
    {
      /* dsocaps points to the .asciz string, and -1 points to the mask
         .long just before the string.  */
      const ElfW(Word) mask = ((const ElfW(Word) *) dsocaps)[-1];
      GLRO(dl_hwcap) |= (uint64_t) mask << _DL_FIRST_EXTRA;
      /* Note that we add the dsocaps to the set already chosen by the
	 LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).
	 So there is no way to request ignoring an OS-supplied dsocap
	 string and bit like you can ignore an OS-supplied HWCAP bit.  */
      hwcap_mask |= (uint64_t) mask << _DL_FIRST_EXTRA;
#if HAVE_TUNABLES
      TUNABLE_SET (glibc, tune, hwcap_mask, uint64_t, hwcap_mask);
#else
      GLRO(dl_hwcap_mask) = hwcap_mask;
#endif
      size_t len;
      for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)
	{
	  uint_fast8_t bit = *p++;
	  len = strlen (p);

	  /* Skip entries that are not enabled in the mask word.  */
	  if (__glibc_likely (mask & ((ElfW(Word)) 1 << bit)))
	    {
	      temp[m].str = p;
	      temp[m].len = len;
	      ++m;
	    }
	  else
	    --cnt;
	}
    }
#endif
  for (n = 0; masked != 0; ++n)
    if ((masked & (1ULL << n)) != 0)
      {
	temp[m].str = _dl_hwcap_string (n);
	temp[m].len = strlen (temp[m].str);
	masked ^= 1ULL << n;
	++m;
      }
  if (platform != NULL)
    {
      temp[m].str = platform;
      temp[m].len = platform_len;
      ++m;
    }

  temp[m].str = "tls";
  temp[m].len = 3;
  ++m;

  assert (m == cnt);

  /* Determine the total size of all strings together.  */
  if (cnt == 1)
    total = temp[0].len + 1;
  else
    {
      total = temp[0].len + temp[cnt - 1].len + 2;
      if (cnt > 2)
	{
	  total <<= 1;
	  for (n = 1; n + 1 < cnt; ++n)
	    total += temp[n].len + 1;
	  if (cnt > 3
	      && (cnt >= sizeof (size_t) * 8
		  || total + (sizeof (*result) << 3)
		     >= (1UL << (sizeof (size_t) * 8 - cnt + 3))))
	    _dl_signal_error (ENOMEM, NULL, NULL,
			      N_("cannot create capability list"));

	  total <<= cnt - 3;
	}
    }

  /* The result structure: we use a very compressed way to store the
     various combinations of capability names.  */
  *sz = 1 << cnt;
  result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);
  if (result == NULL)
    _dl_signal_error (ENOMEM, NULL, NULL,
		      N_("cannot create capability list"));

  if (cnt == 1)
    {
      result[0].str = (char *) (result + *sz);
      result[0].len = temp[0].len + 1;
      result[1].str = (char *) (result + *sz);
      result[1].len = 0;
      cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);
      *cp = '/';
      *sz = 2;
      *max_capstrlen = result[0].len;

      return result;
    }

  /* Fill in the information.  This follows the following scheme
     (indices from TEMP for four strings):
	entry #0: 0, 1, 2, 3	binary: 1111
	      #1: 0, 1, 3		1101
	      #2: 0, 2, 3		1011
	      #3: 0, 3			1001
     This allows the representation of all possible combinations of
     capability names in the string.  First generate the strings.  */
  result[1].str = result[0].str = cp = (char *) (result + *sz);
#define add(idx) \
      cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);
  if (cnt == 2)
    {
      add (1);
      add (0);
    }
  else
    {
      n = 1 << (cnt - 1);
      do
	{
	  n -= 2;

	  /* We always add the last string.  */
	  add (cnt - 1);

	  /* Add the strings which have the bit set in N.  */
	  for (m = cnt - 2; m > 0; --m)
	    if ((n & (1 << m)) != 0)
	      add (m);

	  /* Always add the first string.  */
	  add (0);
	}
      while (n != 0);
    }
#undef add

  /* Now we are ready to install the string pointers and length.  */
  for (n = 0; n < (1UL << cnt); ++n)
    result[n].len = 0;
  n = cnt;
  do
    {
      size_t mask = 1 << --n;

      rp = result;
      for (m = 1 << cnt; m > 0; ++rp)
	if ((--m & mask) != 0)
	  rp->len += temp[n].len + 1;
    }
  while (n != 0);

  /* The first half of the strings all include the first string.  */
  n = (1 << cnt) - 2;
  rp = &result[2];
  while (n != (1UL << (cnt - 1)))
    {
      if ((--n & 1) != 0)
	rp[0].str = rp[-2].str + rp[-2].len;
      else
	rp[0].str = rp[-1].str;
      ++rp;
    }

  /* The second half starts right after the first part of the string of
     the corresponding entry in the first half.  */
  do
    {
      rp[0].str = rp[-(1 << (cnt - 1))].str + temp[cnt - 1].len + 1;
      ++rp;
    }
  while (--n != 0);

  /* The maximum string length.  */
  *max_capstrlen = result[0].len;

  return result;
}