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/*
* arm/cpu_features.c - feature detection for ARM processors
*
* Copyright 2018 Eric Biggers
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
/*
* ARM processors don't have a standard way for unprivileged programs to detect
* processor features. But, on Linux we can read the AT_HWCAP and AT_HWCAP2
* values from /proc/self/auxv.
*
* Ideally we'd use the C library function getauxval(), but it's not guaranteed
* to be available: it was only added to glibc in 2.16, and in Android it was
* added to API level 18 for ARM and level 21 for AArch64.
*/
#include "../cpu_features_common.h" /* must be included first */
#include "cpu_features.h"
#if ARM_CPU_FEATURES_ENABLED
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#define AT_HWCAP 16
#define AT_HWCAP2 26
volatile u32 _cpu_features = 0;
static void scan_auxv(unsigned long *hwcap, unsigned long *hwcap2)
{
int fd;
unsigned long auxbuf[32];
int filled = 0;
int i;
fd = open("/proc/self/auxv", O_RDONLY);
if (fd < 0)
return;
for (;;) {
do {
int ret = read(fd, &((char *)auxbuf)[filled],
sizeof(auxbuf) - filled);
if (ret <= 0) {
if (ret < 0 && errno == EINTR)
continue;
goto out;
}
filled += ret;
} while (filled < 2 * sizeof(long));
i = 0;
do {
unsigned long type = auxbuf[i];
unsigned long value = auxbuf[i + 1];
if (type == AT_HWCAP)
*hwcap = value;
else if (type == AT_HWCAP2)
*hwcap2 = value;
i += 2;
filled -= 2 * sizeof(long);
} while (filled >= 2 * sizeof(long));
memmove(auxbuf, &auxbuf[i], filled);
}
out:
close(fd);
}
static const struct cpu_feature arm_cpu_feature_table[] = {
{ARM_CPU_FEATURE_NEON, "neon"},
{ARM_CPU_FEATURE_PMULL, "pmull"},
{ARM_CPU_FEATURE_CRC32, "crc32"},
};
void setup_cpu_features(void)
{
u32 features = 0;
unsigned long hwcap = 0;
unsigned long hwcap2 = 0;
scan_auxv(&hwcap, &hwcap2);
#ifdef __arm__
STATIC_ASSERT(sizeof(long) == 4);
if (hwcap & (1 << 12)) /* HWCAP_NEON */
features |= ARM_CPU_FEATURE_NEON;
if (hwcap2 & (1 << 1)) /* HWCAP2_PMULL */
features |= ARM_CPU_FEATURE_PMULL;
if (hwcap2 & (1 << 4)) /* HWCAP2_CRC32 */
features |= ARM_CPU_FEATURE_CRC32;
#else
STATIC_ASSERT(sizeof(long) == 8);
if (hwcap & (1 << 1)) /* HWCAP_ASIMD */
features |= ARM_CPU_FEATURE_NEON;
if (hwcap & (1 << 4)) /* HWCAP_PMULL */
features |= ARM_CPU_FEATURE_PMULL;
if (hwcap & (1 << 7)) /* HWCAP_CRC32 */
features |= ARM_CPU_FEATURE_CRC32;
#endif
disable_cpu_features_for_testing(&features, arm_cpu_feature_table,
ARRAY_LEN(arm_cpu_feature_table));
_cpu_features = features | ARM_CPU_FEATURES_KNOWN;
}
#endif /* ARM_CPU_FEATURES_ENABLED */
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