avo/README.md

High-level Golang x86 Assembly Generator

avo aims to make high-performance Go assembly easier to write, review and maintain. It's a Go package that presents a familiar assembly-like interface, together with features to simplify development without sacrificing performance:

• avo programs are Go programs: use control structures for assembly generation
• Register allocation: write your kernels with virtual registers and avo assigns physical registers for you
• Automatic parameter load/stores: ensure memory offsets are always correct even for complex data structures
• Generation of stub files to interface with your Go package

Inspired by the PeachPy and asmjit projects.

Note: avo is still in an experimental phase. APIs subject to change.

Install

Install avo with go get:

$ go get -u github.com/mmcloughlin/avo

Quick Start

avo assembly generators are pure Go programs. Let's get started with a function that adds two uint64 values.

// +build ignore

package main

import (
	. "github.com/mmcloughlin/avo/build"
)

func main() {
	TEXT("Add", "func(x, y uint64) uint64")
	Doc("Add adds x and y.")
	x := Load(Param("x"), GP64())
	y := Load(Param("y"), GP64())
	ADDQ(x, y)
	Store(y, ReturnIndex(0))
	RET()
	Generate()
}

You can go run this code to see the assembly output. To integrate this into the rest of your Go package we recommend a go:generate line to produce the assembly and the corresponding Go stub file.

//go:generate go run asm.go -out add.s -stubs stub.go

After running go generate the add.s file will contain the Go assembly.

// Code generated by command: go run asm.go -out add.s -stubs stub.go. DO NOT EDIT.

// func Add(x uint64, y uint64) uint64
TEXT ·Add(SB), $0-24
	MOVQ	x(FP), AX
	MOVQ	y+8(FP), CX
	ADDQ	AX, CX
	MOVQ	CX, ret+16(FP)
	RET

The same call will produce the stub file stub.go which will enable the function to be called from your Go code.

// Code generated by command: go run asm.go -out add.s -stubs stub.go. DO NOT EDIT.

package add

// Add adds x and y.
func Add(x uint64, y uint64) uint64

See the examples/add directory for the complete working example.

Examples

See examples for the full suite of examples.

Slice Sum

Sum a slice of uint64s:

func main() {
	TEXT("Sum", "func(xs []uint64) uint64")
	Doc("Sum returns the sum of the elements in xs.")
	ptr := Load(Param("xs").Base(), GP64())
	n := Load(Param("xs").Len(), GP64())
	s := GP64()
	XORQ(s, s)
	Label("loop")
	CMPQ(n, Imm(0))
	JE(LabelRef("done"))
	ADDQ(Mem{Base: ptr}, s)
	ADDQ(Imm(8), ptr)
	DECQ(n)
	JMP(LabelRef("loop"))
	Label("done")
	Store(s, ReturnIndex(0))
	RET()
	Generate()
}

Parameter Load/Store

avo provides deconstruction of complex data datatypes into components. For example, load the length of a string argument with:

	TEXT("StringLen", "func(s string) int")
	strlen := Load(Param("s").Len(), GP64())

Index an array:

	TEXT("ArrayThree", "func(a [7]uint64) uint64")
	a3 := Load(Param("a").Index(3), GP64())

Access a struct field (provided you have loaded your package with the Package function):

	TEXT("FieldFloat64", "func(s Struct) float64")
	f64 := Load(Param("s").Field("Float64"), XMM())

Component accesses can be arbitrarily nested:

	TEXT("FieldArrayTwoBTwo", "func(s Struct) byte")
	b2 := Load(Param("s").Field("Array").Index(2).Field("B").Index(2), GP8())

Very similar techniques apply to writing return values. See examples/args and examples/returns for more.

Real Examples

• fnv1a: FNV-1a hash function.
• dot: Vector dot product.
• geohash: Integer geohash encoding.
• sha1: SHA-1 cryptographic hash.
• stadtx: StadtX hash port from dgryski/go-stadtx.

Contributing

Contributions to avo are welcome:

• Feedback from using avo in a real project is incredibly valuable.
• Submit bug reports to the issues page.
• Pull requests accepted. Take a look at outstanding issues for ideas (especially the "good first issue" label).

License

avo is available under the BSD 3-Clause License.