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SIMD(7) Miscellaneous Information Manual SIMD(7)

simd — SIMD enhancements

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:

bcmp S1 S
bcopy S S S SV
bzero S S S
div S S
index A S1
ldiv S S
lldiv S
memchr A S1
memcmp A S S1 S
memccpy S1
memcpy S S S S SV
memmove S S S S SV
memrchr A S1
memset A S S S
rindex A S1 S
stpcpy A S1
stpncpy S1
strcat S1 S
strchr A S1 S
strchrnul A S1
strcmp S S S1 S
strcpy A S1 S S2
strcspn S2
strlcat S1
strlcpy S1
strlen A S S1
strncat S1
strncmp S S S1 S
strncpy S1 S2
strnlen A S1
strrchr A S1 S
strpbrk S2
strsep S2
strspn S2
swab S
timingsafe_bcmp S1
timingsafe_memcmp S
wcschr S
wcscmp S
wcslen S
wmemchr S

: scalar (non-SIMD), : amd64 baseline, : x86-64-v2 or PowerPC 2.05, : x86-64-v3, : x86-64-v4, : PowerPC VSX, : Arm ASIMD (NEON).

On , 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 enhancements only (no SIMD)
cmov, cx8, x87 FPU, fxsr, MMX, osfxsr, SSE, SSE2
cx16, lahf/sahf, popcnt, SSE3, SSSE3, SSE4.1, SSE4.2
AVX, AVX2, BMI1, BMI2, F16C, FMA, lzcnt, movbe, osxsave
AVX-512F/BW/CD/DQ/VL

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.

string(3), arch(7)

H. J. Lu, Michael Matz, Milind Girkar, Jan Hubička, Andreas Jaeger, and Mark Mitchell, AMD64 Architecture Processor Supplement, System V Application Binary Interface, May 23, 2023, Version 1.0.

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, and FreeBSD 12.0 for powerpc64. 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.

Robert Clausecker <fuz@FreeBSD.org>

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.

Use of SIMD enhancements cannot be configured on powerpc64.

June 7, 2024 dev