Implemented an assembler

lib/core/core_linux_arm.q

@@ -0,0 +1,12 @@
+init() {
+	main.main()
+	exit()
+}
+
+exit() {
+	syscall(93, 0)
+}
+
+crash() {
+	syscall(93, 1)
+}

lib/core/core_linux_x86.q

@@ -0,0 +1,12 @@
+init() {
+	main.main()
+	exit()
+}
+
+exit() {
+	syscall(60, 0)
+}
+
+crash() {
+	syscall(60, 1)
+}

lib/core/core_mac.q

@@ -0,0 +1,12 @@
+init() {
+	main.main()
+	exit()
+}
+
+exit() {
+	syscall(0x2000001, 0)
+}
+
+crash() {
+	syscall(0x2000001, 1)
+}

lib/core/core_windows.q

@@ -0,0 +1,28 @@
+init() {
+	// kernel32.SetConsoleCP(cp.utf8)
+	// kernel32.SetConsoleOutputCP(cp.utf8)
+	main.main()
+	exit()
+}
+
+exit() {
+	// kernel32.ExitProcess(0)
+}
+
+crash() {
+	// kernel32.ExitProcess(1)
+}
+
+// const {
+// 	cp {
+// 		utf8 65001
+// 	}
+// }
+
+// extern {
+// 	kernel32 {
+// 		SetConsoleCP(cp uint)
+// 		SetConsoleOutputCP(cp uint)
+// 		ExitProcess(code uint)
+// 	}
+// }

lib/io/write_linux_arm.q

@@ -1,3 +1,3 @@
 write(buffer []byte) -> (written int) {
-	return syscall(64, 0, buffer, len(buffer))
+	return syscall(64, 1, buffer, len(buffer))
 }

lib/io/write_linux_x86.q

@@ -1,3 +1,3 @@
 write(buffer []byte) -> (written int) {
-	return syscall(1, 0, buffer, len(buffer))
+	return syscall(1, 1, buffer, len(buffer))
 }

lib/io/write_mac.q

@@ -0,0 +1,3 @@
+write(buffer []byte) -> (written int) {
+	return syscall(0x2000004, 1, buffer, len(buffer))
+}

lib/io/write_windows.q

@@ -0,0 +1,3 @@
+write(_ []byte) -> (written int) {
+	return 0
+}

src/arm/Registers.go

@@ -40,3 +40,8 @@ const (
 const (
 	ZR = SP // Zero register uses the same numerical value as SP
 )
+
+var CPU = cpu.CPU{
+	Call:    []cpu.Register{X0, X1, X2, X3, X4, X5, X6},
+	Syscall: []cpu.Register{X8, X0, X1, X2, X3, X4, X5},
+}

src/asm/Address.go

@@ -0,0 +1,4 @@
+package asm
+
+// Address represents a memory address.
+type Address = int

src/asm/Assembler.go

@@ -0,0 +1,78 @@
+package asm
+
+import (
+	"maps"
+
+	"git.urbach.dev/cli/q/src/build"
+	"git.urbach.dev/cli/q/src/data"
+	"git.urbach.dev/cli/q/src/elf"
+	"git.urbach.dev/cli/q/src/exe"
+)
+
+// Assembler contains a list of instructions.
+type Assembler struct {
+	Data         data.Data
+	Instructions []Instruction
+}
+
+// Append adds another instruction.
+func (a *Assembler) Append(instr Instruction) {
+	a.Instructions = append(a.Instructions, instr)
+}
+
+// Compile compiles the instructions to machine code.
+func (a *Assembler) Compile(b *build.Build) (code []byte, data []byte) {
+	data, dataLabels := a.Data.Finalize()
+
+	c := compiler{
+		code:       make([]byte, 0, len(a.Instructions)*8),
+		data:       data,
+		dataLabels: dataLabels,
+		labels:     make(map[string]Address, 32),
+	}
+
+	switch b.Arch {
+	case build.ARM:
+		armc := compilerARM{compiler: &c}
+
+		for _, instr := range a.Instructions {
+			armc.Compile(instr)
+		}
+
+	case build.X86:
+		x86c := compilerX86{compiler: &c}
+
+		for _, instr := range a.Instructions {
+			x86c.Compile(instr)
+		}
+	}
+
+	x := exe.New(elf.HeaderEnd, b.FileAlign, b.MemoryAlign)
+	x.InitSections(c.code, c.data)
+	dataSectionOffset := x.Sections[1].MemoryOffset - x.Sections[0].MemoryOffset
+
+	for dataLabel, address := range dataLabels {
+		c.labels[dataLabel] = dataSectionOffset + address
+	}
+
+	for _, call := range c.deferred {
+		call()
+	}
+
+	return c.code, c.data
+}
+
+// Merge combines the contents of this assembler with another one.
+func (a *Assembler) Merge(b *Assembler) {
+	maps.Copy(a.Data, b.Data)
+	a.Instructions = append(a.Instructions, b.Instructions...)
+}
+
+// SetData sets the data for the given label.
+func (a *Assembler) SetData(label string, bytes []byte) {
+	if a.Data == nil {
+		a.Data = data.Data{}
+	}
+
+	a.Data.Insert(label, bytes)
+}

src/asm/Instruction.go

@@ -0,0 +1,34 @@
+package asm
+
+import "git.urbach.dev/cli/q/src/cpu"
+
+type Instruction interface{}
+
+type Call struct {
+	Label string
+}
+
+type FunctionStart struct{}
+type FunctionEnd struct{}
+
+type Label struct {
+	Name string
+}
+
+type MoveRegisterLabel struct {
+	Destination cpu.Register
+	Label       string
+}
+
+type MoveRegisterNumber struct {
+	Destination cpu.Register
+	Number      int
+}
+
+type MoveRegisterRegister struct {
+	Destination cpu.Register
+	Source      cpu.Register
+}
+
+type Return struct{}
+type Syscall struct{}

src/asm/compiler.go

@@ -0,0 +1,13 @@
+package asm
+
+type compiler struct {
+	code       []byte
+	data       []byte
+	dataLabels map[string]Address
+	labels     map[string]Address
+	deferred   []func()
+}
+
+func (c *compiler) Defer(call func()) {
+	c.deferred = append(c.deferred, call)
+}

src/asm/compilerARM.go

@@ -0,0 +1,63 @@
+package asm
+
+import (
+	"encoding/binary"
+
+	"git.urbach.dev/cli/q/src/arm"
+)
+
+type compilerARM struct {
+	*compiler
+}
+
+func (c *compiler) append(code uint32) {
+	c.code = binary.LittleEndian.AppendUint32(c.code, code)
+}
+
+func (c *compilerARM) Compile(instr Instruction) {
+	switch instr := instr.(type) {
+	case *Call:
+		start := len(c.code)
+		c.append(arm.Call(0))
+
+		c.Defer(func() {
+			address, exists := c.labels[instr.Label]
+
+			if !exists {
+				panic("unknown label: " + instr.Label)
+			}
+
+			offset := (address - start) / 4
+			binary.LittleEndian.PutUint32(c.code[start:start+4], arm.Call(offset))
+		})
+	case *FunctionStart:
+		c.append(arm.StorePair(arm.FP, arm.LR, arm.SP, -16))
+		c.append(arm.MoveRegisterRegister(arm.FP, arm.SP))
+	case *FunctionEnd:
+		c.append(arm.LoadPair(arm.FP, arm.LR, arm.SP, 16))
+	case *Label:
+		c.labels[instr.Name] = len(c.code)
+	case *MoveRegisterLabel:
+		start := len(c.code)
+		c.append(arm.LoadAddress(instr.Destination, 0))
+
+		c.Defer(func() {
+			address, exists := c.labels[instr.Label]
+
+			if !exists {
+				panic("unknown label: " + instr.Label)
+			}
+
+			offset := address - start
+			binary.LittleEndian.PutUint32(c.code[start:start+4], arm.LoadAddress(instr.Destination, offset))
+		})
+	case *MoveRegisterNumber:
+		c.code = arm.MoveRegisterNumber(c.code, instr.Destination, instr.Number)
+	case *MoveRegisterRegister:
+		c.append(arm.MoveRegisterRegister(instr.Destination, instr.Source))
+	case *Return:
+		c.append(arm.Return())
+	case *Syscall:
+		c.append(arm.Syscall())
+	}
+}

src/asm/compilerX86.go

@@ -0,0 +1,54 @@
+package asm
+
+import (
+	"encoding/binary"
+
+	"git.urbach.dev/cli/q/src/x86"
+)
+
+type compilerX86 struct {
+	*compiler
+}
+
+func (c *compilerX86) Compile(instr Instruction) {
+	switch instr := instr.(type) {
+	case *Call:
+		c.code = x86.Call(c.code, 0)
+		end := len(c.code)
+
+		c.Defer(func() {
+			address, exists := c.labels[instr.Label]
+
+			if !exists {
+				panic("unknown label: " + instr.Label)
+			}
+
+			offset := address - end
+			binary.LittleEndian.PutUint32(c.code[end-4:end], uint32(offset))
+		})
+	case *Label:
+		c.labels[instr.Name] = len(c.code)
+	case *MoveRegisterLabel:
+		c.code = x86.LoadAddress(c.code, instr.Destination, 0)
+		end := len(c.code)
+
+		c.Defer(func() {
+			address, exists := c.labels[instr.Label]
+
+			if !exists {
+				panic("unknown label: " + instr.Label)
+			}
+
+			offset := address - end
+			binary.LittleEndian.PutUint32(c.code[end-4:end], uint32(offset))
+		})
+	case *MoveRegisterNumber:
+		c.code = x86.MoveRegisterNumber(c.code, instr.Destination, instr.Number)
+	case *MoveRegisterRegister:
+		c.code = x86.MoveRegisterRegister(c.code, instr.Destination, instr.Source)
+	case *Return:
+		c.code = x86.Return(c.code)
+	case *Syscall:
+		c.code = x86.Syscall(c.code)
+	}
+}

src/cli/build.go

@@ -27,7 +27,7 @@ func _build(args []string) int {
 		return 0
 	}
 
-	err = linker.WriteExecutable(b, result)
+	err = linker.WriteFile(b.Executable(), b, result)
 	return exit(err)
 }
 

src/compiler/Compile.go

@@ -16,8 +16,11 @@ func Compile(b *build.Build) (*core.Environment, error) {
 		return nil, err
 	}
 
-	if len(all.Files) == 0 {
+	// Check for existence of `main`
-		return nil, NoInputFiles
+	_, exists := all.Functions["main.main"]
+
+	if !exists {
+		return nil, MissingMainFunction
 	}
 
 	compileFunctions(maps.Values(all.Functions))

src/compiler/Compile_test.go

@@ -19,7 +19,7 @@ func TestNoInputFiles(t *testing.T) {
 	b := build.New(".")
 	_, err := compiler.Compile(b)
 	assert.NotNil(t, err)
-	assert.True(t, errors.Is(err, compiler.NoInputFiles))
+	assert.True(t, errors.Is(err, compiler.MissingMainFunction))
 }
 
 func TestHelloExample(t *testing.T) {

src/compiler/errors.go

@@ -3,5 +3,5 @@ package compiler
 import "git.urbach.dev/cli/q/src/errors"
 
 var (
-	NoInputFiles = errors.String("No input files")
+	MissingMainFunction = errors.String("Missing main function")
 )

src/core/Compile.go

@@ -1,21 +1,28 @@
 package core
 
 import (
+	"slices"
+
+	"git.urbach.dev/cli/q/src/asm"
 	"git.urbach.dev/cli/q/src/cpu"
+	"git.urbach.dev/cli/q/src/ssa"
 	"git.urbach.dev/cli/q/src/token"
 )
 
 // Compile turns a function into machine code.
 func (f *Function) Compile() {
-	registerCount := 0
+	extra := 0
 
-	for _, input := range f.Input {
+	for i, input := range f.Input {
-		f.Identifiers[input.Name] = f.AppendRegister(cpu.Register(registerCount))
+		if input.Name == "_" {
-		registerCount++
+			continue
+		}
+
+		f.Identifiers[input.Name] = f.AppendRegister(i + extra)
 
 		if input.TypeTokens[0].Kind == token.ArrayStart {
-			f.Identifiers[input.Name+".length"] = f.AppendRegister(cpu.Register(registerCount))
+			extra++
-			registerCount++
+			f.Identifiers[input.Name+".length"] = f.AppendRegister(i + extra)
 		}
 	}
 
@@ -28,4 +35,83 @@ func (f *Function) Compile() {
 	}
 
 	f.Err = f.CheckDeadCode()
+
+	if f.Err != nil {
+		return
+	}
+
+	f.Assembler.Append(&asm.Label{Name: f.UniqueName})
+
+	if !f.IsLeaf() && f.UniqueName != "core.init" {
+		f.Assembler.Append(&asm.FunctionStart{})
+	}
+
+	for instr := range f.Values {
+		switch instr := instr.(type) {
+		case *ssa.Call:
+			f.mv(instr.Args[1:], f.CPU.Call)
+
+			switch arg := instr.Args[0].(type) {
+			case *ssa.Function:
+				f.Assembler.Instructions = append(f.Assembler.Instructions, &asm.Call{Label: arg.UniqueName})
+			}
+
+		case *ssa.Syscall:
+			f.mv(instr.Args, f.CPU.Syscall)
+			f.Assembler.Append(&asm.Syscall{})
+
+		case *ssa.Return:
+			f.Assembler.Append(&asm.Return{})
+		}
+	}
+
+	if !f.IsLeaf() && f.UniqueName != "core.init" {
+		f.Assembler.Append(&asm.FunctionEnd{})
+	}
+
+	switch f.Assembler.Instructions[len(f.Assembler.Instructions)-1].(type) {
+	case *asm.Return:
+	default:
+		f.Assembler.Append(&asm.Return{})
+	}
+}
+
+func (f *Function) mv(args []ssa.Value, registers []cpu.Register) {
+	extra := 0
+
+	for _, arg := range args {
+		switch arg.(type) {
+		case *ssa.Bytes:
+			extra++
+		}
+	}
+
+	for i, arg := range slices.Backward(args) {
+		switch arg := arg.(type) {
+		case *ssa.Int:
+			f.Assembler.Append(&asm.MoveRegisterNumber{
+				Destination: registers[i+extra],
+				Number:      arg.Int,
+			})
+		case *ssa.Parameter:
+			f.Assembler.Append(&asm.MoveRegisterRegister{
+				Destination: registers[i+extra],
+				Source:      f.CPU.Call[arg.Index],
+			})
+		case *ssa.Bytes:
+			f.Assembler.SetData("data0", arg.Bytes)
+
+			f.Assembler.Append(&asm.MoveRegisterNumber{
+				Destination: registers[i+extra],
+				Number:      len(arg.Bytes),
+			})
+
+			extra--
+
+			f.Assembler.Append(&asm.MoveRegisterLabel{
+				Destination: registers[i+extra],
+				Label:       "data0",
+			})
+		}
+	}
 }

src/core/CompileInstruction.go

@@ -15,6 +15,10 @@ func (f *Function) CompileInstruction(instr token.List) error {
 
 	expr := expression.Parse(instr)
 
+	if expr == nil {
+		return nil
+	}
+
 	if expr.Token.Kind == token.Define {
 		name := expr.Children[0].String(f.File.Bytes)
 		value, err := f.Evaluate(expr.Children[1])

src/core/Evaluate.go

@@ -2,6 +2,7 @@ package core
 
 import (
 	"fmt"
+	"slices"
 
 	"git.urbach.dev/cli/q/src/errors"
 	"git.urbach.dev/cli/q/src/expression"
@@ -18,7 +19,16 @@ func (f *Function) Evaluate(expr *expression.Expression) (ssa.Value, error) {
 			value, exists := f.Identifiers[name]
 
 			if !exists {
-				return nil, errors.New(&UnknownIdentifier{Name: name}, f.File, expr.Token.Position)
+				function, exists := f.All.Functions[f.File.Package+"."+name]
+
+				if !exists {
+					return nil, errors.New(&UnknownIdentifier{Name: name}, f.File, expr.Token.Position)
+				}
+
+				f.Dependencies.Add(function)
+				v := f.AppendFunction(function.UniqueName)
+				v.Source = expr.Token
+				return v, nil
 			}
 
 			return value, nil
@@ -66,7 +76,7 @@ func (f *Function) Evaluate(expr *expression.Expression) (ssa.Value, error) {
 
 		args := make([]ssa.Value, len(children))
 
-		for i, child := range children {
+		for i, child := range slices.Backward(children) {
 			value, err := f.Evaluate(child)
 
 			if err != nil {
@@ -93,8 +103,17 @@ func (f *Function) Evaluate(expr *expression.Expression) (ssa.Value, error) {
 		}
 
 	case token.Dot:
-		name := fmt.Sprintf("%s.%s", expr.Children[0].String(f.File.Bytes), expr.Children[1].String(f.File.Bytes))
+		left := expr.Children[0]
-		v := f.AppendFunction(name)
+		right := expr.Children[1]
+		label := fmt.Sprintf("%s.%s", left.String(f.File.Bytes), right.String(f.File.Bytes))
+		function, exists := f.All.Functions[label]
+
+		if !exists {
+			return nil, errors.New(&UnknownIdentifier{Name: label}, f.File, left.Token.Position)
+		}
+
+		f.Dependencies.Add(function)
+		v := f.AppendFunction(function.UniqueName)
 		v.Source = expr.Children[1].Token
 		return v, nil
 	}

src/core/Function.go

@@ -3,7 +3,10 @@ package core
 import (
 	"fmt"
 
+	"git.urbach.dev/cli/q/src/asm"
+	"git.urbach.dev/cli/q/src/cpu"
 	"git.urbach.dev/cli/q/src/fs"
+	"git.urbach.dev/cli/q/src/set"
 	"git.urbach.dev/cli/q/src/ssa"
 	"git.urbach.dev/cli/q/src/token"
 )
@@ -11,14 +14,18 @@ import (
 // Function is the smallest unit of code.
 type Function struct {
 	ssa.IR
-	Name        string
+	Name         string
-	UniqueName  string
+	UniqueName   string
-	File        *fs.File
+	File         *fs.File
-	Input       []*Parameter
+	Input        []*Parameter
-	Output      []*Parameter
+	Output       []*Parameter
-	Body        token.List
+	Body         token.List
-	Identifiers map[string]ssa.Value
+	Identifiers  map[string]ssa.Value
-	Err         error
+	All          *Environment
+	Dependencies set.Ordered[*Function]
+	Assembler    asm.Assembler
+	CPU          *cpu.CPU
+	Err          error
 }
 
 // NewFunction creates a new function.
@@ -33,6 +40,24 @@ func NewFunction(name string, file *fs.File) *Function {
 				{Instructions: make([]ssa.Value, 0, 8)},
 			},
 		},
+		Assembler: asm.Assembler{
+			Instructions: make([]asm.Instruction, 0, 8),
+		},
+	}
+}
+
+// EachDependency recursively finds all the calls to other functions.
+// It avoids calling the same function twice with the help of a hashmap.
+func (f *Function) EachDependency(traversed map[*Function]bool, call func(*Function)) {
+	call(f)
+	traversed[f] = true
+
+	for dep := range f.Dependencies.All() {
+		if traversed[dep] {
+			continue
+		}
+
+		dep.EachDependency(traversed, call)
 	}
 }
 
@@ -41,6 +66,11 @@ func (f *Function) IsExtern() bool {
 	return f.Body == nil
 }
 
+// IsLeaf returns true if the function doesn't call other functions.
+func (f *Function) IsLeaf() bool {
+	return f.Dependencies.Count() == 0
+}
+
 // String returns the unique name.
 func (f *Function) String() string {
 	return f.UniqueName

src/cpu/CPU.go

@@ -0,0 +1,7 @@
+package cpu
+
+// CPU represents the processor.
+type CPU struct {
+	Call    []Register
+	Syscall []Register
+}

src/data/Data.go

@@ -0,0 +1,4 @@
+package data
+
+// Data saves slices of bytes referenced by labels.
+type Data map[string][]byte

src/data/Data_test.go

@@ -0,0 +1,28 @@
+package data_test
+
+import (
+	"testing"
+
+	"git.urbach.dev/cli/q/src/data"
+	"git.urbach.dev/go/assert"
+)
+
+func TestInterning(t *testing.T) {
+	d := data.Data{}
+	d.Insert("label1", []byte("Hello"))
+	d.Insert("label2", []byte("ello"))
+	raw, positions := d.Finalize()
+	assert.DeepEqual(t, raw, []byte("Hello"))
+	assert.Equal(t, positions["label1"], 0)
+	assert.Equal(t, positions["label2"], 1)
+}
+
+func TestInterningReverse(t *testing.T) {
+	d := data.Data{}
+	d.Insert("label1", []byte("ello"))
+	d.Insert("label2", []byte("Hello"))
+	raw, positions := d.Finalize()
+	assert.DeepEqual(t, raw, []byte("Hello"))
+	assert.Equal(t, positions["label1"], 1)
+	assert.Equal(t, positions["label2"], 0)
+}

src/data/Finalize.go

@@ -0,0 +1,41 @@
+package data
+
+import (
+	"bytes"
+	"sort"
+)
+
+// Finalize returns the final raw data slice and a map of labels with their respective indices.
+// It will try to reuse existing data whenever possible.
+func (data Data) Finalize() ([]byte, map[string]int) {
+	var (
+		keys      = make([]string, 0, len(data))
+		positions = make(map[string]int, len(data))
+		capacity  = 0
+	)
+
+	for key, value := range data {
+		keys = append(keys, key)
+		capacity += len(value)
+	}
+
+	sort.SliceStable(keys, func(i, j int) bool {
+		return len(data[keys[i]]) > len(data[keys[j]])
+	})
+
+	final := make([]byte, 0, capacity)
+
+	for _, key := range keys {
+		raw := data[key]
+		position := bytes.Index(final, raw)
+
+		if position != -1 {
+			positions[key] = position
+		} else {
+			positions[key] = len(final)
+			final = append(final, raw...)
+		}
+	}
+
+	return final, positions
+}

src/data/Insert.go

@@ -0,0 +1,6 @@
+package data
+
+// Insert registers a slice of bytes for the given label.
+func (data Data) Insert(label string, raw []byte) {
+	data[label] = raw
+}

src/data/bench_test.go

@@ -0,0 +1,21 @@
+package data_test
+
+import (
+	"testing"
+
+	"git.urbach.dev/cli/q/src/data"
+)
+
+func BenchmarkFinalize(b *testing.B) {
+	d := data.Data{}
+	d.Insert("1", []byte("Beautiful is better than ugly."))
+	d.Insert("2", []byte("Explicit is better than implicit."))
+	d.Insert("3", []byte("Simple is better than complex."))
+	d.Insert("4", []byte("Complex is better than complicated."))
+	d.Insert("5", []byte("Flat is better than nested."))
+	d.Insert("6", []byte("Sparse is better than dense."))
+
+	for b.Loop() {
+		d.Finalize()
+	}
+}

src/linker/WriteExecutable.go

@@ -1,50 +0,0 @@
-package linker
-
-import (
-	"encoding/binary"
-	"os"
-
-	"git.urbach.dev/cli/q/src/arm"
-	"git.urbach.dev/cli/q/src/build"
-	"git.urbach.dev/cli/q/src/core"
-	"git.urbach.dev/cli/q/src/elf"
-	"git.urbach.dev/cli/q/src/x86"
-)
-
-// WriteExecutable writes an executable file to disk.
-func WriteExecutable(b *build.Build, result *core.Environment) error {
-	executable := b.Executable()
-	file, err := os.Create(executable)
-
-	if err != nil {
-		return err
-	}
-
-	code := []byte{}
-	data := []byte{}
-
-	switch b.Arch {
-	case build.ARM:
-		code = arm.MoveRegisterNumber(code, arm.X8, 93)
-		code = arm.MoveRegisterNumber(code, arm.X0, 0)
-		code = binary.LittleEndian.AppendUint32(code, arm.Syscall())
-
-	case build.X86:
-		code = x86.MoveRegisterNumber(code, x86.R0, 60)
-		code = x86.MoveRegisterNumber(code, x86.R7, 0)
-		code = x86.Syscall(code)
-	}
-
-	switch b.OS {
-	case build.Linux:
-		elf.Write(file, b, code, data)
-	}
-
-	err = file.Close()
-
-	if err != nil {
-		return err
-	}
-
-	return os.Chmod(executable, 0755)
-}

src/linker/WriteFile.go

@@ -0,0 +1,49 @@
+package linker
+
+import (
+	"os"
+
+	"git.urbach.dev/cli/q/src/asm"
+	"git.urbach.dev/cli/q/src/build"
+	"git.urbach.dev/cli/q/src/core"
+	"git.urbach.dev/cli/q/src/data"
+	"git.urbach.dev/cli/q/src/elf"
+)
+
+// WriteFile writes an executable file to disk.
+func WriteFile(executable string, b *build.Build, env *core.Environment) error {
+	file, err := os.Create(executable)
+
+	if err != nil {
+		return err
+	}
+
+	init := env.Functions["core.init"]
+	traversed := make(map[*core.Function]bool, len(env.Functions))
+
+	final := asm.Assembler{
+		Instructions: make([]asm.Instruction, 0, 8),
+		Data:         make(data.Data, 32),
+	}
+
+	// This will place the main function immediately after the entry point
+	// and also add everything the main function calls recursively.
+	init.EachDependency(traversed, func(f *core.Function) {
+		final.Merge(&f.Assembler)
+	})
+
+	code, data := final.Compile(b)
+
+	switch b.OS {
+	case build.Linux:
+		elf.Write(file, b, code, data)
+	}
+
+	err = file.Close()
+
+	if err != nil {
+		return err
+	}
+
+	return os.Chmod(executable, 0755)
+}

src/linker/WriteFile_test.go

@@ -11,7 +11,7 @@ import (
 	"git.urbach.dev/go/assert"
 )
 
-func TestWriteExecutable(t *testing.T) {
+func TestWriteFile(t *testing.T) {
 	tmpDir := filepath.Join(os.TempDir(), "q", "tests")
 	err := os.MkdirAll(tmpDir, 0755)
 	assert.Nil(t, err)
@@ -29,10 +29,10 @@ func TestWriteExecutable(t *testing.T) {
 	assert.Nil(t, err)
 
 	b.SetArch(build.ARM)
-	err = linker.WriteExecutable(b, env)
+	err = linker.WriteFile(b.Executable(), b, env)
 	assert.Nil(t, err)
 
 	b.SetArch(build.X86)
-	err = linker.WriteExecutable(b, env)
+	err = linker.WriteFile(b.Executable(), b, env)
 	assert.Nil(t, err)
 }

src/scanner/Scan.go

@@ -1,9 +1,12 @@
 package scanner
 
 import (
+	"path/filepath"
+
 	"git.urbach.dev/cli/q/src/build"
 	"git.urbach.dev/cli/q/src/core"
 	"git.urbach.dev/cli/q/src/fs"
+	"git.urbach.dev/cli/q/src/global"
 )
 
 // Scan scans all the files included in the build.
@@ -16,6 +19,7 @@ func Scan(b *build.Build) (*core.Environment, error) {
 	}
 
 	go func() {
+		s.queueDirectory(filepath.Join(global.Library, "core"), "core")
 		s.queue(b.Files...)
 		s.group.Wait()
 		close(s.functions)
@@ -36,6 +40,7 @@ func Scan(b *build.Build) (*core.Environment, error) {
 				continue
 			}
 
+			f.All = all
 			all.Functions[f.UniqueName] = f
 
 		case file, ok := <-s.files:

src/scanner/scanFunction.go

@@ -1,9 +1,12 @@
 package scanner
 
 import (
+	"git.urbach.dev/cli/q/src/arm"
+	"git.urbach.dev/cli/q/src/build"
 	"git.urbach.dev/cli/q/src/errors"
 	"git.urbach.dev/cli/q/src/fs"
 	"git.urbach.dev/cli/q/src/token"
+	"git.urbach.dev/cli/q/src/x86"
 )
 
 // scanFunction scans a function.
@@ -67,6 +70,13 @@ func (s *scanner) scanFunction(file *fs.File, tokens token.List, i int) (int, er
 		return i, errors.New(ExpectedFunctionDefinition, file, tokens[i].Position)
 	}
 
+	switch s.build.Arch {
+	case build.ARM:
+		function.CPU = &arm.CPU
+	case build.X86:
+		function.CPU = &x86.CPU
+	}
+
 	function.Body = tokens[bodyStart:i]
 	s.functions <- function
 	return i, nil

src/set/Ordered.go

@@ -0,0 +1,38 @@
+package set
+
+import (
+	"iter"
+	"slices"
+)
+
+// Ordered is an ordered set.
+type Ordered[T comparable] struct {
+	values []T
+}
+
+// Add adds a value to the set if it doesn't exist yet.
+// It returns `false` if it already exists, `true` if it was added.
+func (set *Ordered[T]) Add(value T) bool {
+	if slices.Contains(set.values, value) {
+		return false
+	}
+
+	set.values = append(set.values, value)
+	return true
+}
+
+// All returns an iterator over all the values in the set.
+func (set *Ordered[T]) All() iter.Seq[T] {
+	return func(yield func(T) bool) {
+		for _, value := range set.values {
+			if !yield(value) {
+				return
+			}
+		}
+	}
+}
+
+// Count returns the number of elements in the set.
+func (set *Ordered[T]) Count() int {
+	return len(set.values)
+}

src/ssa/IR.go

@@ -1,9 +1,5 @@
 package ssa
 
-import (
-	"git.urbach.dev/cli/q/src/cpu"
-)
-
 // IR is a list of basic blocks.
 type IR struct {
 	Blocks []*Block
@@ -44,8 +40,8 @@ func (f *IR) AppendInt(x int) *Int {
 }
 
 // AppendRegister adds a new register value to the last block.
-func (f *IR) AppendRegister(reg cpu.Register) *Register {
+func (f *IR) AppendRegister(index int) *Parameter {
-	v := &Register{Register: reg}
+	v := &Parameter{Index: uint8(index)}
 	f.Append(v)
 	return v
 }

src/ssa/Parameter.go

@@ -0,0 +1,31 @@
+package ssa
+
+import "fmt"
+
+type Parameter struct {
+	Index uint8
+	Liveness
+	HasToken
+}
+
+func (v *Parameter) Dependencies() []Value {
+	return nil
+}
+
+func (a *Parameter) Equals(v Value) bool {
+	b, sameType := v.(*Parameter)
+
+	if !sameType {
+		return false
+	}
+
+	return a.Index == b.Index
+}
+
+func (v *Parameter) IsConst() bool {
+	return true
+}
+
+func (v *Parameter) String() string {
+	return fmt.Sprintf("arg[%d]", v.Index)
+}

src/ssa/Register.go

@@ -1,31 +0,0 @@
-package ssa
-
-import "git.urbach.dev/cli/q/src/cpu"
-
-type Register struct {
-	Register cpu.Register
-	Liveness
-	HasToken
-}
-
-func (v *Register) Dependencies() []Value {
-	return nil
-}
-
-func (a *Register) Equals(v Value) bool {
-	b, sameType := v.(*Register)
-
-	if !sameType {
-		return false
-	}
-
-	return a.Register == b.Register
-}
-
-func (v *Register) IsConst() bool {
-	return true
-}
-
-func (v *Register) String() string {
-	return v.Register.String()
-}

src/x86/Registers.go

@@ -20,3 +20,8 @@ const (
 	R14
 	R15
 )
+
+var CPU = cpu.CPU{
+	Call:    []cpu.Register{R0, R7, R6, R2, R10, R8, R9},
+	Syscall: []cpu.Register{R0, R7, R6, R2, R10, R8, R9},
+}

tests/examples_test.go

@@ -0,0 +1,81 @@
+package tests_test
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.urbach.dev/cli/q/src/build"
+	"git.urbach.dev/cli/q/src/compiler"
+	"git.urbach.dev/cli/q/src/linker"
+	"git.urbach.dev/go/assert"
+)
+
+var examples = []struct {
+	Name     string
+	Input    string
+	Output   string
+	ExitCode int
+}{
+	{"hello", "", "Hello\n", 0},
+}
+
+func TestExamples(t *testing.T) {
+	for _, test := range examples {
+		directory := filepath.Join("..", "examples", test.Name)
+		run(t, directory, test.Input, test.Output, test.ExitCode)
+	}
+}
+
+func BenchmarkExamples(b *testing.B) {
+	for _, test := range examples {
+		b.Run(test.Name, func(b *testing.B) {
+			example := build.New(filepath.Join("..", "examples", test.Name))
+
+			for b.Loop() {
+				_, err := compiler.Compile(example)
+				assert.Nil(b, err)
+			}
+		})
+	}
+}
+
+// run builds and runs the file to check if the output matches the expected output.
+func run(t *testing.T, path string, input string, expectedOutput string, expectedExitCode int) {
+	b := build.New(path)
+	env, err := compiler.Compile(b)
+	assert.Nil(t, err)
+
+	tmpDir := filepath.Join(os.TempDir(), "q", "tests")
+	err = os.MkdirAll(tmpDir, 0755)
+	assert.Nil(t, err)
+
+	executable := b.Executable()
+	executable = filepath.Join(tmpDir, filepath.Base(executable))
+	err = linker.WriteFile(executable, b, env)
+	assert.Nil(t, err)
+
+	stat, err := os.Stat(executable)
+	assert.Nil(t, err)
+	assert.True(t, stat.Size() > 0)
+
+	cmd := exec.Command(executable)
+	cmd.Stdin = strings.NewReader(input)
+	output, err := cmd.Output()
+	exitCode := 0
+
+	if err != nil {
+		exitError, ok := err.(*exec.ExitError)
+
+		if !ok {
+			t.Fatal(exitError)
+		}
+
+		exitCode = exitError.ExitCode()
+	}
+
+	assert.Equal(t, exitCode, expectedExitCode)
+	assert.DeepEqual(t, string(output), expectedOutput)
+}