elf/dl-hwcaps.h

   1 /* Hardware capability support for run-time dynamic loader.
   2    Copyright (C) 2017-2024 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 */