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
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

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.

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, 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.

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.