SIMD(7) FreeBSD Miscellaneous Information Manual SIMD(7)
NAME
simd - SIMD enhancements
DESCRIPTION
On some architectures, the FreeBSD libc provides enhanced implementations
of commonly used functions, replacing the architecture-independent
implementations used otherwise. Depending on architecture and function,
an enhanced implementation of a function may either always be used or the
libc detects at runtime which SIMD instruction set extensions are
supported and picks the most suitable implementation automatically. On
amd64, the environment variable ARCHLEVEL can be used to override this
mechanism.
Enhanced functions are present for the following architectures:
FUNCTION AARCH64 ARM AMD64 I386 PPC64 RISC-V
bcmp A S1 S
bcopy A S S S SV S
bzero A S S S S
div S S
index A S1 S
ldiv S S
lldiv S
memchr A S1 S
memcmp A S S1 S
memccpy A S1
memcpy A S S S SV S
memmove A S S S SV
memrchr A S1
memset A S S S S
rindex A S1 S S
stpcpy A S1
stpncpy S1
strcat A S1 S
strchr A S1 S S
strchrnul A S1 S
strcmp A S S1 S
strcpy A S1 S S2
strcspn S S2
strlcat A S1
strlcpy A S1
strlen A S S1 S
strncat A S1
strncmp A S S1 S
strncpy S1 S2
strnlen A S1 S
strrchr A S1 S S
strpbrk S S2
strsep S S2
strspn S S2
swab S
timingsafe_bcmp A S1
timingsafe_memcmp S S
wcschr S
wcscmp S
wcslen S
wmemchr S
S: scalar (non-SIMD), 1: amd64 baseline, 2: x86-64-v2 or PowerPC 2.05,
3: x86-64-v3, 4: x86-64-v4, V: PowerPC VSX, A: Arm ASIMD (NEON).
ENVIRONMENT
ARCHLEVEL
On amd64, controls the level of SIMD enhancements used. If this
variable is set to an architecture level from the list below and
that architecture level is supported by the processor, SIMD
enhancements up to ARCHLEVEL are used. If ARCHLEVEL is unset,
not recognised, or not supported by the processor, the highest
level of SIMD enhancements supported by the processor is used.
A suffix beginning with `:' or `+' in ARCHLEVEL is ignored and
may be used for future extensions. The architecture level can be
prefixed with a `!' character to force use of the requested
architecture level, even if the processor does not advertise that
it is supported. This usually causes applications to crash and
should only be used for testing purposes or if architecture level
detection yields incorrect results.
The architecture levels follow the AMD64 SysV ABI supplement:
scalar scalar enhancements only (no SIMD)
baseline cmov, cx8, x87 FPU, fxsr, MMX, osfxsr, SSE, SSE2
x86-64-v2 cx16, lahf/sahf, popcnt, SSE3, SSSE3, SSE4.1, SSE4.2
x86-64-v3 AVX, AVX2, BMI1, BMI2, F16C, FMA, lzcnt, movbe,
osxsave
x86-64-v4 AVX-512F/BW/CD/DQ/VL
DIAGNOSTICS
Illegal Instruction Printed by sh(1) if a command is terminated through
delivery of a SIGILL signal, see signal(3).
Use of an unsupported architecture level was forced by setting ARCHLEVEL
to a string beginning with a `!' character, causing a process to crash
due to use of an unsupported instruction. Unset ARCHLEVEL, remove the
`!' prefix or select a supported architecture level.
Message may also appear for unrelated reasons.
SEE ALSO
string(3), arch(7)
H. J. Lu, Michael Matz, Milind Girkar, Jan Hubicka, Andreas Jaeger, and
Mark Mitchell, "AMD64 Architecture Processor Supplement", System V
Application Binary Interface, May 23, 2023, Version 1.0.
HISTORY
Architecture-specific enhanced libc functions were added starting with
FreeBSD 2.0 for i386, FreeBSD 6.0 for arm, FreeBSD 6.1 for amd64,
FreeBSD 11.0 for aarch64, FreeBSD 12.0 for powerpc64, and FreeBSD 16.0
for riscv64. SIMD-enhanced functions were first added with FreeBSD 13.0
for powerpc64 and with FreeBSD 14.1 for amd64.
A simd manual page appeared in FreeBSD 14.1.
AUTHOR
Robert Clausecker <fuz@FreeBSD.org>
CAVEATS
Other parts of FreeBSD such as cryptographic routines in the kernel or in
OpenSSL may also use SIMD enhancements. These enhancements are not
subject to the ARCHLEVEL variable and may have their own configuration
mechanism.
BUGS
Use of SIMD enhancements cannot be configured on powerpc64.
FreeBSD 15.1-STABLE-HBSD October 21, 2025 SIMD(7)