1 /* Hardware capability support for run-time dynamic loader.
2 Copyright (C) 2017-2023 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 <https://www.gnu.org/licenses/>. */
18
19 #ifndef _DL_HWCAPS_H
20 #define _DL_HWCAPS_H
21
22 #include <stdint.h>
23 #include <stddef.h>
24
25 #include <elf/dl-tunables.h>
26
27 #define GLIBC_HWCAPS_SUBDIRECTORY "glibc-hwcaps"
28 #define GLIBC_HWCAPS_PREFIX GLIBC_HWCAPS_SUBDIRECTORY "/"
29
30 /* Used by _dl_hwcaps_split below, to split strings at ':'
31 separators. */
32 struct dl_hwcaps_split
33 {
34 const char *segment; /* Start of the current segment. */
35 size_t length; /* Number of bytes until ':' or NUL. */
36 };
37
38 /* Prepare *S to parse SUBJECT, for future _dl_hwcaps_split calls. If
39 SUBJECT is NULL, it is treated as the empty string. */
40 static inline void
41 _dl_hwcaps_split_init (struct dl_hwcaps_split *s, const char *subject)
42 {
43 s->segment = subject;
44 /* The initial call to _dl_hwcaps_split will not skip anything. */
45 s->length = 0;
46 }
47
48 /* Extract the next non-empty string segment, up to ':' or the null
49 terminator. Return true if one more segment was found, or false if
50 the end of the string was reached. On success, S->segment is the
51 start of the segment found, and S->length is its length.
52 (Typically, S->segment[S->length] is not null.) */
53 _Bool _dl_hwcaps_split (struct dl_hwcaps_split *s) attribute_hidden;
54
55 /* Similar to dl_hwcaps_split, but with bit-based and name-based
56 masking. */
57 struct dl_hwcaps_split_masked
58 {
59 struct dl_hwcaps_split split;
60
61 /* For used by the iterator implementation. */
62 const char *mask;
63 uint32_t bitmask;
64 };
65
66 /* Prepare *S for iteration with _dl_hwcaps_split_masked. Only HWCAP
67 names in SUBJECT whose bit is set in BITMASK and whose name is in
68 MASK will be returned. SUBJECT must not contain empty HWCAP names.
69 If MASK is NULL, no name-based masking is applied. Likewise for
70 BITMASK if BITMASK is -1 (infinite number of bits). */
71 static inline void
72 _dl_hwcaps_split_masked_init (struct dl_hwcaps_split_masked *s,
73 const char *subject,
74 uint32_t bitmask, const char *mask)
75 {
76 _dl_hwcaps_split_init (&s->split, subject);
77 s->bitmask = bitmask;
78 s->mask = mask;
79 }
80
81 /* Like _dl_hwcaps_split, but apply masking. */
82 _Bool _dl_hwcaps_split_masked (struct dl_hwcaps_split_masked *s)
83 attribute_hidden;
84
85 /* Returns true if the colon-separated HWCAP list HWCAPS contains the
86 capability NAME (with length NAME_LENGTH). If HWCAPS is NULL, the
87 function returns true. */
88 _Bool _dl_hwcaps_contains (const char *hwcaps, const char *name,
89 size_t name_length) attribute_hidden;
90
91 /* Colon-separated string of glibc-hwcaps subdirectories, without the
92 "glibc-hwcaps/" prefix. The most preferred subdirectory needs to
93 be listed first. Up to 32 subdirectories are supported, limited by
94 the width of the uint32_t mask. */
95 extern const char _dl_hwcaps_subdirs[] attribute_hidden;
96
97 /* Returns a bitmap of active subdirectories in _dl_hwcaps_subdirs.
98 Bit 0 (the LSB) corresponds to the first substring in
99 _dl_hwcaps_subdirs, bit 1 to the second substring, and so on.
100 There is no direct correspondence between HWCAP bitmasks and this
101 bitmask. */
102 uint32_t _dl_hwcaps_subdirs_active (void) attribute_hidden;
103
104 /* Returns a bitmask that marks the last ACTIVE subdirectories in a
105 _dl_hwcaps_subdirs_active string (containing SUBDIRS directories in
106 total) as active. Intended for use in _dl_hwcaps_subdirs_active
107 implementations (if a contiguous tail of the list in
108 _dl_hwcaps_subdirs is selected). */
109 static inline uint32_t
110 _dl_hwcaps_subdirs_build_bitmask (int subdirs, int active)
111 {
112 /* Leading subdirectories that are not active. */
113 int inactive = subdirs - active;
114 if (inactive == 32)
115 return 0;
116
117 uint32_t mask;
118 if (subdirs != 32)
119 mask = (1U << subdirs) - 1;
120 else
121 mask = -1;
122 return mask ^ ((1U << inactive) - 1);
123 }
124
125 /* Pre-computed glibc-hwcaps subdirectory priorities. Used in
126 dl-cache.c to quickly find the proprieties for the stored HWCAP
127 names. */
128 struct dl_hwcaps_priority
129 {
130 /* The name consists of name_length bytes at name (not necessarily
131 null-terminated). */
132 const char *name;
133 uint32_t name_length;
134
135 /* Priority of this name. A positive number. */
136 uint32_t priority;
137 };
138
139 /* Pre-computed hwcaps priorities. Set up by
140 _dl_important_hwcaps. */
141 extern struct dl_hwcaps_priority *_dl_hwcaps_priorities attribute_hidden;
142 extern uint32_t _dl_hwcaps_priorities_length attribute_hidden;
143
144 #endif /* _DL_HWCAPS_H */