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. */
36const struct r_strlenpair *
37internal_function
38_dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
39 size_t *max_capstrlen)
40{
41 uint64_t hwcap_mask = GET_HWCAP_MASK();
42 /* Determine how many important bits are set. */
43 uint64_t masked = GLRO(dl_hwcap) & hwcap_mask;
44 size_t cnt = platform != NULL;
45 size_t n, m;
46 size_t total;
47 struct r_strlenpair *result;
48 struct r_strlenpair *rp;
49 char *cp;
50
51 /* Count the number of bits set in the masked value. */
52 for (n = 0; (~((1ULL << n) - 1) & masked) != 0; ++n)
53 if ((masked & (1ULL << n)) != 0)
54 ++cnt;
55
56#ifdef NEED_DL_SYSINFO_DSO
57 /* The system-supplied DSO can contain a note of type 2, vendor "GNU".
58 This gives us a list of names to treat as fake hwcap bits. */
59
60 const char *dsocaps = NULL;
61 size_t dsocapslen = 0;
62 if (GLRO(dl_sysinfo_map) != NULL)
63 {
64 const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
65 const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
66 for (uint_fast16_t i = 0; i < phnum; ++i)
67 if (phdr[i].p_type == PT_NOTE)
68 {
69 const ElfW(Addr) start = (phdr[i].p_vaddr
70 + GLRO(dl_sysinfo_map)->l_addr);
71 /* The standard ELF note layout is exactly as the anonymous struct.
72 The next element is a variable length vendor name of length
73 VENDORLEN (with a real length rounded to ElfW(Word)), followed
74 by the data of length DATALEN (with a real length rounded to
75 ElfW(Word)). */
76 const struct
77 {
78 ElfW(Word) vendorlen;
79 ElfW(Word) datalen;
80 ElfW(Word) type;
81 } *note = (const void *) start;
82 while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
83 {
84#define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word)))
85 /* The layout of the type 2, vendor "GNU" note is as follows:
86 .long <Number of capabilities enabled by this note>
87 .long <Capabilities mask> (as mask >> _DL_FIRST_EXTRA).
88 .byte <The bit number for the next capability>
89 .asciz <The name of the capability>. */
90 if (note->type == NT_GNU_HWCAP
91 && note->vendorlen == sizeof "GNU"
92 && !memcmp ((note + 1), "GNU", sizeof "GNU")
93 && note->datalen > 2 * sizeof (ElfW(Word)) + 2)
94 {
95 const ElfW(Word) *p = ((const void *) (note + 1)
96 + ROUND (sizeof "GNU"));
97 cnt += *p++;
98 ++p; /* Skip mask word. */
99 dsocaps = (const char *) p; /* Pseudo-string "<b>name" */
100 dsocapslen = note->datalen - sizeof *p * 2;
101 break;
102 }
103 note = ((const void *) (note + 1)
104 + ROUND (note->vendorlen) + ROUND (note->datalen));
105#undef ROUND
106 }
107 if (dsocaps != NULL)
108 break;
109 }
110 }
111#endif
112
113 /* For TLS enabled builds always add 'tls'. */
114 ++cnt;
115
116 /* Create temporary data structure to generate result table. */
117 struct r_strlenpair temp[cnt];
118 m = 0;
119#ifdef NEED_DL_SYSINFO_DSO
120 if (dsocaps != NULL)
121 {
122 /* dsocaps points to the .asciz string, and -1 points to the mask
123 .long just before the string. */
124 const ElfW(Word) mask = ((const ElfW(Word) *) dsocaps)[-1];
125 GLRO(dl_hwcap) |= (uint64_t) mask << _DL_FIRST_EXTRA;
126 /* Note that we add the dsocaps to the set already chosen by the
127 LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).
128 So there is no way to request ignoring an OS-supplied dsocap
129 string and bit like you can ignore an OS-supplied HWCAP bit. */
130 hwcap_mask |= (uint64_t) mask << _DL_FIRST_EXTRA;
131#if HAVE_TUNABLES
132 TUNABLE_SET (glibc, tune, hwcap_mask, uint64_t, hwcap_mask);
133#else
134 GLRO(dl_hwcap_mask) = hwcap_mask;
135#endif
136 size_t len;
137 for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)
138 {
139 uint_fast8_t bit = *p++;
140 len = strlen (p);
141
142 /* Skip entries that are not enabled in the mask word. */
143 if (__glibc_likely (mask & ((ElfW(Word)) 1 << bit)))
144 {
145 temp[m].str = p;
146 temp[m].len = len;
147 ++m;
148 }
149 else
150 --cnt;
151 }
152 }
153#endif
154 for (n = 0; masked != 0; ++n)
155 if ((masked & (1ULL << n)) != 0)
156 {
157 temp[m].str = _dl_hwcap_string (n);
158 temp[m].len = strlen (temp[m].str);
159 masked ^= 1ULL << n;
160 ++m;
161 }
162 if (platform != NULL)
163 {
164 temp[m].str = platform;
165 temp[m].len = platform_len;
166 ++m;
167 }
168
169 temp[m].str = "tls";
170 temp[m].len = 3;
171 ++m;
172
173 assert (m == cnt);
174
175 /* Determine the total size of all strings together. */
176 if (cnt == 1)
177 total = temp[0].len + 1;
178 else
179 {
180 total = temp[0].len + temp[cnt - 1].len + 2;
181 if (cnt > 2)
182 {
183 total <<= 1;
184 for (n = 1; n + 1 < cnt; ++n)
185 total += temp[n].len + 1;
186 if (cnt > 3
187 && (cnt >= sizeof (size_t) * 8
188 || total + (sizeof (*result) << 3)
189 >= (1UL << (sizeof (size_t) * 8 - cnt + 3))))
190 _dl_signal_error (ENOMEM, NULL, NULL,
191 N_("cannot create capability list"));
192
193 total <<= cnt - 3;
194 }
195 }
196
197 /* The result structure: we use a very compressed way to store the
198 various combinations of capability names. */
199 *sz = 1 << cnt;
200 result = (struct r_strlenpair *) malloc (*sz * sizeof (*result) + total);
201 if (result == NULL)
202 _dl_signal_error (ENOMEM, NULL, NULL,
203 N_("cannot create capability list"));
204
205 if (cnt == 1)
206 {
207 result[0].str = (char *) (result + *sz);
208 result[0].len = temp[0].len + 1;
209 result[1].str = (char *) (result + *sz);
210 result[1].len = 0;
211 cp = __mempcpy ((char *) (result + *sz), temp[0].str, temp[0].len);
212 *cp = '/';
213 *sz = 2;
214 *max_capstrlen = result[0].len;
215
216 return result;
217 }
218
219 /* Fill in the information. This follows the following scheme
220 (indices from TEMP for four strings):
221 entry #0: 0, 1, 2, 3 binary: 1111
222 #1: 0, 1, 3 1101
223 #2: 0, 2, 3 1011
224 #3: 0, 3 1001
225 This allows the representation of all possible combinations of
226 capability names in the string. First generate the strings. */
227 result[1].str = result[0].str = cp = (char *) (result + *sz);
228#define add(idx) \
229 cp = __mempcpy (__mempcpy (cp, temp[idx].str, temp[idx].len), "/", 1);
230 if (cnt == 2)
231 {
232 add (1);
233 add (0);
234 }
235 else
236 {
237 n = 1 << (cnt - 1);
238 do
239 {
240 n -= 2;
241
242 /* We always add the last string. */
243 add (cnt - 1);
244
245 /* Add the strings which have the bit set in N. */
246 for (m = cnt - 2; m > 0; --m)
247 if ((n & (1 << m)) != 0)
248 add (m);
249
250 /* Always add the first string. */
251 add (0);
252 }
253 while (n != 0);
254 }
255#undef add
256
257 /* Now we are ready to install the string pointers and length. */
258 for (n = 0; n < (1UL << cnt); ++n)
259 result[n].len = 0;
260 n = cnt;
261 do
262 {
263 size_t mask = 1 << --n;
264
265 rp = result;
266 for (m = 1 << cnt; m > 0; ++rp)
267 if ((--m & mask) != 0)
268 rp->len += temp[n].len + 1;
269 }
270 while (n != 0);
271
272 /* The first half of the strings all include the first string. */
273 n = (1 << cnt) - 2;
274 rp = &result[2];
275 while (n != (1UL << (cnt - 1)))
276 {
277 if ((--n & 1) != 0)
278 rp[0].str = rp[-2].str + rp[-2].len;
279 else
280 rp[0].str = rp[-1].str;
281 ++rp;
282 }
283
284 /* The second half starts right after the first part of the string of
285 the corresponding entry in the first half. */
286 do
287 {
288 rp[0].str = rp[-(1 << (cnt - 1))].str + temp[cnt - 1].len + 1;
289 ++rp;
290 }
291 while (--n != 0);
292
293 /* The maximum string length. */
294 *max_capstrlen = result[0].len;
295
296 return result;
297}
298