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/* Support routines to query GLIBC_TUNABLES=glibc.cpu.hwcaps
Copyright 2025-2026 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
#include <stdlib.h>
#include <string.h>
#include "cpu-supports.h"
/* Allow reparsing of env var for testing. */
bool hwcap_allowed_nocache = false;
extern bool
hwcap_allowed (char const *glibc_hwcap)
{
if (! glibc_hwcap)
return true;
if (*glibc_hwcap != '-') /* Need to pass HWCAP with a leading - */
return true;
/* Match how GLIBC parses tunables as indicated with:
GLIBC_TUNABLES=glibc.cpu.hwcaps=... ld.so --list-tunables | grep hwcaps
GLIBC_TUNABLES items are delimited with ':',
and like glibc we take the last instance of glibc.cpu.hwcaps.
An example of the usual format is:
GLIBC_TUNABLES=glibc.cpu.hwcaps=-AVX,-AVX2 */
static char const *hwcaps;
if (hwcap_allowed_nocache || ! hwcaps)
{ /* Cache glibc.cpu.hwcaps once per process. */
if ((hwcaps = getenv ("GLIBC_TUNABLES")))
{
char const *tunables_start = hwcaps;
char const *last_hwcaps;
while ((last_hwcaps = strstr (hwcaps, "glibc.cpu.hwcaps=")))
hwcaps = last_hwcaps + sizeof "glibc.cpu.hwcaps=" - 1;
if (hwcaps == tunables_start) /* No match. */
hwcaps = "";
}
else
hwcaps = "";
}
if (! hwcaps) /* Shouldn't happen. */
return true;
if (! *hwcaps)
return true;
char const *sentinel = strchr (hwcaps, ':');
if (! sentinel)
sentinel = hwcaps + strlen (hwcaps);
char const *cap = hwcaps;
while ((cap = strstr (cap, glibc_hwcap)) && cap < sentinel)
{ /* Check it's not a partial match. */
cap += strlen (glibc_hwcap);
if (*cap == ',' || *cap == ':' || *cap == '\0')
return false; /* Feature disabled. */
/* glibc hwcaps can't have '-' in name so ok to search from here. */
}
return true;
}
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