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/* x86 CPU feature tuning.
This file is part of the GNU C Library.
Copyright (C) 2017-2022 Free Software Foundation, Inc.
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/>. */
#if HAVE_TUNABLES
# define TUNABLE_NAMESPACE cpu
# include <stdbool.h>
# include <stdint.h>
# include <unistd.h> /* Get STDOUT_FILENO for _dl_printf. */
# include <elf/dl-tunables.h>
# include <string.h>
# include <cpu-features.h>
# include <ldsodefs.h>
/* We can't use IFUNC memcmp nor strlen in init_cpu_features from libc.a
since IFUNC must be set up by init_cpu_features. */
# if defined USE_MULTIARCH && !defined SHARED
# ifdef __x86_64__
# define DEFAULT_MEMCMP __memcmp_sse2
# else
# define DEFAULT_MEMCMP __memcmp_ia32
# endif
extern __typeof (memcmp) DEFAULT_MEMCMP;
# else
# define DEFAULT_MEMCMP memcmp
# endif
# define CHECK_GLIBC_IFUNC_CPU_OFF(f, cpu_features, name, len) \
_Static_assert (sizeof (#name) - 1 == len, #name " != " #len); \
if (!DEFAULT_MEMCMP (f, #name, len)) \
{ \
CPU_FEATURE_UNSET (cpu_features, name) \
break; \
}
/* Disable a preferred feature NAME. We don't enable a preferred feature
which isn't available. */
# define CHECK_GLIBC_IFUNC_PREFERRED_OFF(f, cpu_features, name, len) \
_Static_assert (sizeof (#name) - 1 == len, #name " != " #len); \
if (!DEFAULT_MEMCMP (f, #name, len)) \
{ \
cpu_features->preferred[index_arch_##name] \
&= ~bit_arch_##name; \
break; \
}
/* Enable/disable a preferred feature NAME. */
# define CHECK_GLIBC_IFUNC_PREFERRED_BOTH(f, cpu_features, name, \
disable, len) \
_Static_assert (sizeof (#name) - 1 == len, #name " != " #len); \
if (!DEFAULT_MEMCMP (f, #name, len)) \
{ \
if (disable) \
cpu_features->preferred[index_arch_##name] &= ~bit_arch_##name; \
else \
cpu_features->preferred[index_arch_##name] |= bit_arch_##name; \
break; \
}
/* Enable/disable a preferred feature NAME. Enable a preferred feature
only if the feature NEED is usable. */
# define CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH(f, cpu_features, name, \
need, disable, len) \
_Static_assert (sizeof (#name) - 1 == len, #name " != " #len); \
if (!DEFAULT_MEMCMP (f, #name, len)) \
{ \
if (disable) \
cpu_features->preferred[index_arch_##name] &= ~bit_arch_##name; \
else if (CPU_FEATURE_USABLE_P (cpu_features, need)) \
cpu_features->preferred[index_arch_##name] |= bit_arch_##name; \
break; \
}
attribute_hidden
void
TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
{
/* The current IFUNC selection is based on microbenchmarks in glibc.
It should give the best performance for most workloads. But other
choices may have better performance for a particular workload or on
the hardware which wasn't available when the selection was made.
The environment variable:
GLIBC_TUNABLES=glibc.cpu.hwcaps=-xxx,yyy,-zzz,....
can be used to enable CPU/ARCH feature yyy, disable CPU/ARCH feature
yyy and zzz, where the feature name is case-sensitive and has to
match the ones in cpu-features.h. It can be used by glibc developers
to tune for a new processor or override the IFUNC selection to
improve performance for a particular workload.
NOTE: the IFUNC selection may change over time. Please check all
multiarch implementations when experimenting. */
const char *p = valp->strval;
struct cpu_features *cpu_features = &GLRO(dl_x86_cpu_features);
size_t len;
do
{
const char *c, *n;
bool disable;
size_t nl;
for (c = p; *c != ','; c++)
if (*c == '\0')
break;
len = c - p;
disable = *p == '-';
if (disable)
{
n = p + 1;
nl = len - 1;
}
else
{
n = p;
nl = len;
}
switch (nl)
{
default:
break;
case 3:
if (disable)
{
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX, 3);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, CX8, 3);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, FMA, 3);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, HTT, 3);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, IBT, 3);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, RTM, 3);
}
break;
case 4:
if (disable)
{
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX2, 4);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, BMI1, 4);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, BMI2, 4);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, CMOV, 4);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, ERMS, 4);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, FMA4, 4);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE2, 4);
CHECK_GLIBC_IFUNC_PREFERRED_OFF (n, cpu_features, I586, 4);
CHECK_GLIBC_IFUNC_PREFERRED_OFF (n, cpu_features, I686, 4);
}
break;
case 5:
if (disable)
{
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, LZCNT, 5);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, MOVBE, 5);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SHSTK, 5);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSSE3, 5);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, XSAVE, 5);
}
break;
case 6:
if (disable)
{
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, POPCNT, 6);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE4_1, 6);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE4_2, 6);
if (!DEFAULT_MEMCMP (n, "XSAVEC", 6))
{
/* Update xsave_state_size to XSAVE state size. */
cpu_features->xsave_state_size
= cpu_features->xsave_state_full_size;
CPU_FEATURE_UNSET (cpu_features, XSAVEC);
}
}
break;
case 7:
if (disable)
{
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512F, 7);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, OSXSAVE, 7);
}
break;
case 8:
if (disable)
{
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512CD, 8);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512BW, 8);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512DQ, 8);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512ER, 8);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512PF, 8);
CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512VL, 8);
}
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Slow_BSF,
disable, 8);
break;
case 11:
{
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
Prefer_ERMS,
disable, 11);
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
Prefer_FSRM,
disable, 11);
CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH (n, cpu_features,
Slow_SSE4_2,
SSE4_2,
disable, 11);
}
break;
case 15:
{
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
Fast_Rep_String,
disable, 15);
}
break;
case 16:
{
CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
(n, cpu_features, Prefer_No_AVX512, AVX512F,
disable, 16);
}
break;
case 18:
{
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
Fast_Copy_Backward,
disable, 18);
}
break;
case 19:
{
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
Fast_Unaligned_Load,
disable, 19);
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
Fast_Unaligned_Copy,
disable, 19);
}
break;
case 20:
{
CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
(n, cpu_features, Prefer_No_VZEROUPPER, AVX, disable,
20);
}
break;
case 23:
{
CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
(n, cpu_features, AVX_Fast_Unaligned_Load, AVX,
disable, 23);
}
break;
case 24:
{
CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
(n, cpu_features, MathVec_Prefer_No_AVX512, AVX512F,
disable, 24);
}
break;
case 26:
{
CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
(n, cpu_features, Prefer_PMINUB_for_stringop, SSE2,
disable, 26);
}
break;
}
p += len + 1;
}
while (*p != '\0');
}
# if CET_ENABLED
attribute_hidden
void
TUNABLE_CALLBACK (set_x86_ibt) (tunable_val_t *valp)
{
if (DEFAULT_MEMCMP (valp->strval, "on", sizeof ("on")) == 0)
GL(dl_x86_feature_control).ibt = cet_always_on;
else if (DEFAULT_MEMCMP (valp->strval, "off", sizeof ("off")) == 0)
GL(dl_x86_feature_control).ibt = cet_always_off;
else if (DEFAULT_MEMCMP (valp->strval, "permissive",
sizeof ("permissive")) == 0)
GL(dl_x86_feature_control).ibt = cet_permissive;
}
attribute_hidden
void
TUNABLE_CALLBACK (set_x86_shstk) (tunable_val_t *valp)
{
if (DEFAULT_MEMCMP (valp->strval, "on", sizeof ("on")) == 0)
GL(dl_x86_feature_control).shstk = cet_always_on;
else if (DEFAULT_MEMCMP (valp->strval, "off", sizeof ("off")) == 0)
GL(dl_x86_feature_control).shstk = cet_always_off;
else if (DEFAULT_MEMCMP (valp->strval, "permissive",
sizeof ("permissive")) == 0)
GL(dl_x86_feature_control).shstk = cet_permissive;
}
# endif
#endif
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