<!--{
	"Title": "A Quick Guide to Go's Assembler",
	"Path":  "/doc/asm"
}-->

<h2 id="introduction">A Quick Guide to Go's Assembler</h2>

<p>
This document is a quick outline of the unusual form of assembly language used by the <code>gc</code> Go compiler.
The document is not comprehensive.
</p>

<p>
The assembler is based on the input style of the Plan 9 assemblers, which is documented in detail

			targetAddr.Type = obj.TYPE_REG
		}
	case target.Type == obj.TYPE_CONST:
		// JMP $4
		*targetAddr = a[0]
	case target.Type == obj.TYPE_NONE:
		// JMP
	default:
		p.errorf("cannot assemble jump %+v", target)
		return
	}

	p.append(prog, cond, true)
}

func (p *Parser) patch() {
	for _, patch := range p.toPatch {
		targetProg := p.labels[patch.label]
		if targetProg == nil {

// license that can be found in the LICENSE file.

// This file encapsulates some of the odd characteristics of the
// Loong64 (LoongArch64) instruction set, to minimize its interaction
// with the core of the assembler.

package arch

import (
	"cmd/internal/obj"
	"cmd/internal/obj/loong64"
)

func jumpLoong64(word string) bool {
	switch word {

			break
		}
	}
	if ok && !*flags.SymABIs {
		ctxt.NumberSyms()
		obj.WriteObjFile(ctxt, buf)
	}
	if !ok || diag {
		if failedFile != "" {
			log.Printf("assembly of %s failed", failedFile)
		} else {
			log.Print("assembly failed")
		}
		buf.Close()
		os.Remove(*flags.OutputFile)
		os.Exit(1)
	}

// license that can be found in the LICENSE file.

// This file encapsulates some of the odd characteristics of the ARM
// instruction set, to minimize its interaction with the core of the
// assembler.

package arch

import (
	"strings"

	"cmd/internal/obj"
	"cmd/internal/obj/arm"
)

var armLS = map[string]uint8{
	"U":  arm.C_UBIT,
	"S":  arm.C_SBIT,
	"W":  arm.C_WBIT,

// license that can be found in the LICENSE file.

// This file encapsulates some of the odd characteristics of the RISCV64
// instruction set, to minimize its interaction with the core of the
// assembler.

package arch

import (
	"cmd/internal/obj"
	"cmd/internal/obj/riscv"
)

// IsRISCV64AMO reports whether the op (as defined by a riscv.A*
// constant) is one of the AMO instructions that requires special

		// Some systems use leading _ to denote non-assembly symbols.
		return s == "__cgodebug_ints" || s == "___cgodebug_ints"
	}
	isDebugFloats := func(s string) bool {
		// Some systems use leading _ to denote non-assembly symbols.
		return s == "__cgodebug_floats" || s == "___cgodebug_floats"
	}
	indexOfDebugStr := func(s string) int {
		// Some systems use leading _ to denote non-assembly symbols.
		if strings.HasPrefix(s, "___") {

// license that can be found in the LICENSE file.

// The cases are auto-generated by disassembler.
// The uncommented cases means they can be handled by assembler
// and they are consistent with disassembler decoding.
// TODO means they cannot be handled by current assembler.

#include "../../../../../runtime/textflag.h"

TEXT asmtest(SB),DUPOK|NOSPLIT,$-8

// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package asm implements the parser and instruction generator for the assembler.
// TODO: Split apart?
package asm

import (
	"fmt"
	"io"
	"log"
	"os"
	"strconv"
	"strings"
	"text/scanner"
	"unicode/utf8"

	"cmd/asm/internal/arch"
	"cmd/asm/internal/flags"

// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This input was created by taking the instruction productions in
// the old assembler's (7a's) grammar and hand-writing complete
// instructions for each rule, to guarantee we cover the same space.

#include "../../../../../runtime/textflag.h"

TEXT	foo(SB), DUPOK|NOSPLIT, $-8

// arithmetic operations