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/* Hardware capability support for run-time dynamic loader.
Copyright (C) 2012-2025 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
<https://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>
/* This is the result of counting the substrings in a colon-separated
hwcaps string. */
struct hwcaps_counts
{
/* Number of substrings. */
size_t count;
/* Sum of the individual substring lengths (without separators or
null terminators). */
size_t total_length;
/* Maximum length of an individual substring. */
size_t maximum_length;
};
/* Update *COUNTS according to the contents of HWCAPS. Skip over
entries whose bit is not set in MASK. */
static void
update_hwcaps_counts (struct hwcaps_counts *counts, const char *hwcaps,
uint32_t bitmask, const char *mask)
{
struct dl_hwcaps_split_masked sp;
_dl_hwcaps_split_masked_init (&sp, hwcaps, bitmask, mask);
while (_dl_hwcaps_split_masked (&sp))
{
++counts->count;
counts->total_length += sp.split.length;
if (sp.split.length > counts->maximum_length)
counts->maximum_length = sp.split.length;
}
}
/* State for copy_hwcaps. Must be initialized to point to
the storage areas for the array and the strings themselves. */
struct copy_hwcaps
{
struct r_strlenpair *next_pair;
char *next_string;
};
/* Copy HWCAPS into the string pairs and strings, advancing *TARGET.
Skip over entries whose bit is not set in MASK. */
static void
copy_hwcaps (struct copy_hwcaps *target, const char *hwcaps,
uint32_t bitmask, const char *mask)
{
struct dl_hwcaps_split_masked sp;
_dl_hwcaps_split_masked_init (&sp, hwcaps, bitmask, mask);
while (_dl_hwcaps_split_masked (&sp))
{
target->next_pair->str = target->next_string;
char *slash = __mempcpy (__mempcpy (target->next_string,
GLIBC_HWCAPS_PREFIX,
strlen (GLIBC_HWCAPS_PREFIX)),
sp.split.segment, sp.split.length);
*slash = '/';
target->next_pair->len
= strlen (GLIBC_HWCAPS_PREFIX) + sp.split.length + 1;
++target->next_pair;
target->next_string = slash + 1;
}
}
struct dl_hwcaps_priority *_dl_hwcaps_priorities;
uint32_t _dl_hwcaps_priorities_length;
/* Allocate _dl_hwcaps_priorities and fill it with data. */
static void
compute_priorities (size_t total_count, const char *prepend,
uint32_t bitmask, const char *mask)
{
_dl_hwcaps_priorities = malloc (total_count
* sizeof (*_dl_hwcaps_priorities));
if (_dl_hwcaps_priorities == NULL)
_dl_signal_error (ENOMEM, NULL, NULL,
N_("cannot create HWCAP priorities"));
_dl_hwcaps_priorities_length = total_count;
/* First the prepended subdirectories. */
size_t i = 0;
{
struct dl_hwcaps_split sp;
_dl_hwcaps_split_init (&sp, prepend);
while (_dl_hwcaps_split (&sp))
{
_dl_hwcaps_priorities[i].name = sp.segment;
_dl_hwcaps_priorities[i].name_length = sp.length;
_dl_hwcaps_priorities[i].priority = i + 1;
++i;
}
}
/* Then the built-in subdirectories that are actually active. */
{
struct dl_hwcaps_split_masked sp;
_dl_hwcaps_split_masked_init (&sp, _dl_hwcaps_subdirs, bitmask, mask);
while (_dl_hwcaps_split_masked (&sp))
{
_dl_hwcaps_priorities[i].name = sp.split.segment;
_dl_hwcaps_priorities[i].name_length = sp.split.length;
_dl_hwcaps_priorities[i].priority = i + 1;
++i;
}
}
assert (i == total_count);
}
/* Sort the _dl_hwcaps_priorities array by name. */
static void
sort_priorities_by_name (void)
{
/* Insertion sort. There is no need to link qsort into the dynamic
loader for such a short array. */
for (size_t i = 1; i < _dl_hwcaps_priorities_length; ++i)
for (size_t j = i; j > 0; --j)
{
struct dl_hwcaps_priority *previous = _dl_hwcaps_priorities + j - 1;
struct dl_hwcaps_priority *current = _dl_hwcaps_priorities + j;
/* Bail out if current is greater or equal to the previous
value. */
uint32_t to_compare;
if (current->name_length < previous->name_length)
to_compare = current->name_length;
else
to_compare = previous->name_length;
int cmp = memcmp (current->name, previous->name, to_compare);
if (cmp > 0
|| (cmp == 0 && current->name_length >= previous->name_length))
break;
/* Swap *previous and *current. */
struct dl_hwcaps_priority tmp = *previous;
*previous = *current;
*current = tmp;
}
}
/* Return an array of useful/necessary hardware capability names. */
const struct r_strlenpair *
_dl_important_hwcaps (const char *glibc_hwcaps_prepend,
const char *glibc_hwcaps_mask,
size_t *sz, size_t *max_capstrlen)
{
/* glibc-hwcaps subdirectories. */
uint32_t hwcaps_subdirs_active = _dl_hwcaps_subdirs_active ();
struct hwcaps_counts hwcaps_counts = { 0, };
update_hwcaps_counts (&hwcaps_counts, glibc_hwcaps_prepend, -1, NULL);
update_hwcaps_counts (&hwcaps_counts, _dl_hwcaps_subdirs,
hwcaps_subdirs_active, glibc_hwcaps_mask);
compute_priorities (hwcaps_counts.count, glibc_hwcaps_prepend,
hwcaps_subdirs_active, glibc_hwcaps_mask);
sort_priorities_by_name ();
/* Each hwcaps subdirectory has a GLIBC_HWCAPS_PREFIX string prefix
and a "/" suffix once stored in the result. */
hwcaps_counts.maximum_length += strlen (GLIBC_HWCAPS_PREFIX) + 1;
size_t total = (hwcaps_counts.count * (strlen (GLIBC_HWCAPS_PREFIX) + 1)
+ hwcaps_counts.total_length);
*sz = hwcaps_counts.count + 1;
/* This is the overall result. */
struct r_strlenpair *overall_result
= malloc (*sz * sizeof (*overall_result) + total);
if (overall_result == NULL)
_dl_signal_error (ENOMEM, NULL, NULL,
N_("cannot create capability list"));
/* Fill in the glibc-hwcaps subdirectories. */
{
struct copy_hwcaps target;
target.next_pair = overall_result;
target.next_string = (char *) (overall_result + *sz);
copy_hwcaps (&target, glibc_hwcaps_prepend, -1, NULL);
copy_hwcaps (&target, _dl_hwcaps_subdirs,
hwcaps_subdirs_active, glibc_hwcaps_mask);
/* Append an empty entry for the base directory itself. */
target.next_pair->str = target.next_string;
target.next_pair->len = 0;
}
/* The maximum string length. */
*max_capstrlen = hwcaps_counts.maximum_length;
return overall_result;
}
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