Added Windows support

docs/pe.md

@@ -0,0 +1,27 @@
+# Portable Executable
+
+## Notes
+
+Unlike Linux, Windows does not ignore zero-length sections at the end of a file and will
+fail loading them because they don't exist within the file. Adding a single byte to the
+section can fix this problem, but it's easier to just remove the section header entirely.
+The solution used here is to guarantee that the data section is never empty by always
+importing a few core functions from "kernel32.dll".
+
+## DLL function pointers
+
+The section where the DLL function pointers are stored does not need to be marked as writable.
+The Windows executable loader resolves the pointers before they are loaded into memory.
+
+The stack must be 16 byte aligned before a DLL function is called.
+
+## Links
+
+- https://learn.microsoft.com/en-us/windows/win32/debug/pe-format
+- https://learn.microsoft.com/en-us/previous-versions/ms809762(v=msdn.10)
+- https://learn.microsoft.com/en-us/archive/msdn-magazine/2002/february/inside-windows-win32-portable-executable-file-format-in-detail
+- https://learn.microsoft.com/en-us/archive/msdn-magazine/2002/march/inside-windows-an-in-depth-look-into-the-win32-portable-executable-file-format-part-2
+- https://blog.kowalczyk.info/articles/pefileformat.html
+- https://keyj.emphy.de/win32-pe/
+- https://corkamiwiki.github.io/PE
+- https://github.com/ayaka14732/TinyPE-on-Win10

lib/core/core_windows.q

@@ -1,28 +1,23 @@
 init() {
-	// kernel32.SetConsoleCP(cp.utf8)
+	utf8 := 65001
-	// kernel32.SetConsoleOutputCP(cp.utf8)
+	kernel32.SetConsoleCP(utf8)
+	kernel32.SetConsoleOutputCP(utf8)
 	main.main()
 	exit()
 }
 
 exit() {
-	// kernel32.ExitProcess(0)
+	kernel32.ExitProcess(0)
 }
 
 crash() {
-	// kernel32.ExitProcess(1)
+	kernel32.ExitProcess(1)
 }
 
-// const {
+extern {
-// 	cp {
+	kernel32 {
-// 		utf8 65001
+		SetConsoleCP(cp uint)
-// 	}
+		SetConsoleOutputCP(cp uint)
-// }
+		ExitProcess(code uint)
-
+	}
-// extern {
+}
-// 	kernel32 {
-// 		SetConsoleCP(cp uint)
-// 		SetConsoleOutputCP(cp uint)
-// 		ExitProcess(code uint)
-// 	}
-// }

lib/io/write_windows.q

@@ -1,3 +1,10 @@
 write(_ []byte) -> (written int) {
 	return 0
 }
+
+extern {
+	kernel32 {
+		GetStdHandle(handle int64) -> int64
+		WriteConsoleA(fd int64, buffer *byte, length uint32, written *uint32) -> bool
+	}
+}

src/arm/Registers.go

@@ -44,4 +44,5 @@ const (
 var CPU = cpu.CPU{
 	Call:       []cpu.Register{X0, X1, X2, X3, X4, X5, X6},
 	Syscall:    []cpu.Register{X8, X0, X1, X2, X3, X4, X5},
+	ExternCall: []cpu.Register{X0, X1, X2, X3, X4, X5, X6, X7},
 }

src/asm/Assembler.go

@@ -5,6 +5,7 @@ import (
 
 	"git.urbach.dev/cli/q/src/build"
 	"git.urbach.dev/cli/q/src/data"
+	"git.urbach.dev/cli/q/src/dll"
 	"git.urbach.dev/cli/q/src/elf"
 	"git.urbach.dev/cli/q/src/exe"
 )
@@ -13,6 +14,7 @@ import (
 type Assembler struct {
 	Data         data.Data
 	Instructions []Instruction
+	Libraries    dll.List
 }
 
 // Append adds another instruction.
@@ -30,7 +32,7 @@ func (a *Assembler) Last() Instruction {
 }
 
 // Compile compiles the instructions to machine code.
-func (a *Assembler) Compile(b *build.Build) (code []byte, data []byte) {
+func (a *Assembler) Compile(b *build.Build) (code []byte, data []byte, libs dll.List) {
 	data, dataLabels := a.Data.Finalize()
 
 	c := compiler{
@@ -38,6 +40,7 @@ func (a *Assembler) Compile(b *build.Build) (code []byte, data []byte) {
 		data:       data,
 		dataLabels: dataLabels,
 		labels:     make(map[string]Address, 32),
+		libraries:  a.Libraries,
 	}
 
 	switch b.Arch {
@@ -57,18 +60,22 @@ func (a *Assembler) Compile(b *build.Build) (code []byte, data []byte) {
 	}
 
 	x := exe.New(elf.HeaderEnd, b.FileAlign, b.MemoryAlign)
-	x.InitSections(c.code, c.data)
+	x.InitSections(c.code, c.data, nil)
 	dataSectionOffset := x.Sections[1].MemoryOffset - x.Sections[0].MemoryOffset
 
 	for dataLabel, address := range dataLabels {
 		c.labels[dataLabel] = dataSectionOffset + address
 	}
 
+	if b.OS == build.Windows {
+		c.importsStart = x.Sections[2].MemoryOffset - x.Sections[0].MemoryOffset
+	}
+
 	for _, call := range c.deferred {
 		call()
 	}
 
-	return c.code, c.data
+	return c.code, c.data, c.libraries
 }
 
 // Merge combines the contents of this assembler with another one.
@@ -81,6 +88,12 @@ func (a *Assembler) Merge(b *Assembler) {
 
 	a.Instructions = append(a.Instructions, b.Instructions[skip:]...)
 	maps.Copy(a.Data, b.Data)
+
+	for _, library := range b.Libraries {
+		for _, fn := range library.Functions {
+			a.Libraries = a.Libraries.Append(library.Name, fn)
+		}
+	}
 }
 
 // SetData sets the data for the given label.

src/asm/Assembler_test.go

@@ -37,9 +37,9 @@ func TestAssembler(t *testing.T) {
 	final.Merge(b)
 	final.Merge(c)
 
-	code, _ := final.Compile(&build.Build{Arch: build.ARM})
+	code, _, _ := final.Compile(&build.Build{Arch: build.ARM})
 	assert.NotNil(t, code)
 
-	code, _ = final.Compile(&build.Build{Arch: build.X86})
+	code, _, _ = final.Compile(&build.Build{Arch: build.X86})
 	assert.NotNil(t, code)
 }

src/asm/Instruction.go

@@ -4,10 +4,21 @@ import "git.urbach.dev/cli/q/src/cpu"
 
 type Instruction interface{}
 
+type AndRegisterNumber struct {
+	Destination cpu.Register
+	Source      cpu.Register
+	Number      int
+}
+
 type Call struct {
 	Label string
 }
 
+type CallExtern struct {
+	Library  string
+	Function string
+}
+
 type FunctionStart struct{}
 type FunctionEnd struct{}
 
@@ -35,4 +46,11 @@ type MoveRegisterRegister struct {
 }
 
 type Return struct{}
+
+type SubRegisterNumber struct {
+	Destination cpu.Register
+	Source      cpu.Register
+	Number      int
+}
+
 type Syscall struct{}

src/asm/compiler.go

@@ -1,10 +1,14 @@
 package asm
 
+import "git.urbach.dev/cli/q/src/dll"
+
 type compiler struct {
 	code         []byte
 	data         []byte
 	dataLabels   map[string]Address
 	labels       map[string]Address
+	libraries    dll.List
+	importsStart int
 	deferred     []func()
 }
 

src/asm/compilerX86.go

@@ -2,6 +2,7 @@ package asm
 
 import (
 	"encoding/binary"
+	"fmt"
 
 	"git.urbach.dev/cli/q/src/sizeof"
 	"git.urbach.dev/cli/q/src/x86"
@@ -13,6 +14,18 @@ type compilerX86 struct {
 
 func (c *compilerX86) Compile(instr Instruction) {
 	switch instr := instr.(type) {
+	case *AndRegisterNumber:
+		if instr.Destination != instr.Source {
+			c.code = x86.MoveRegisterRegister(c.code, instr.Destination, instr.Source)
+		}
+
+		c.code = x86.AndRegisterNumber(c.code, instr.Destination, instr.Number)
+	case *SubRegisterNumber:
+		if instr.Destination != instr.Source {
+			c.code = x86.MoveRegisterRegister(c.code, instr.Destination, instr.Source)
+		}
+
+		c.code = x86.SubRegisterNumber(c.code, instr.Destination, instr.Number)
 	case *Call:
 		c.code = x86.Call(c.code, 0)
 		end := len(c.code)
@@ -24,6 +37,21 @@ func (c *compilerX86) Compile(instr Instruction) {
 				panic("unknown label: " + instr.Label)
 			}
 
+			offset := address - end
+			binary.LittleEndian.PutUint32(c.code[end-4:end], uint32(offset))
+		})
+	case *CallExtern:
+		c.code = x86.CallAt(c.code, 0)
+		end := len(c.code)
+
+		c.Defer(func() {
+			index := c.libraries.Index(instr.Library, instr.Function)
+
+			if index == -1 {
+				panic(fmt.Sprintf("unknown extern function '%s' in library '%s'", instr.Function, instr.Library))
+			}
+
+			address := c.importsStart + index*8
 			offset := address - end
 			binary.LittleEndian.PutUint32(c.code[end-4:end], uint32(offset))
 		})

src/core/Compile.go

@@ -7,6 +7,7 @@ import (
 	"git.urbach.dev/cli/q/src/cpu"
 	"git.urbach.dev/cli/q/src/ssa"
 	"git.urbach.dev/cli/q/src/types"
+	"git.urbach.dev/cli/q/src/x86"
 )
 
 // Compile turns a function into machine code.
@@ -72,11 +73,19 @@ func (f *Function) Compile() {
 	for instr := range f.Values {
 		switch instr := instr.(type) {
 		case *ssa.Call:
-			f.mv(instr.Arguments[1:], f.CPU.Call)
+			arg := instr.Arguments[0].(*ssa.Function)
+			fn := f.All.Functions[arg.UniqueName]
 
-			switch arg := instr.Arguments[0].(type) {
+			if fn.IsExtern() {
-			case *ssa.Function:
+				f.mv(instr.Arguments[1:], f.CPU.ExternCall)
-				f.Assembler.Instructions = append(f.Assembler.Instructions, &asm.Call{Label: arg.UniqueName})
+				f.Assembler.Append(&asm.MoveRegisterRegister{Destination: x86.R5, Source: x86.SP})
+				f.Assembler.Append(&asm.AndRegisterNumber{Destination: x86.SP, Source: x86.SP, Number: -16})
+				f.Assembler.Append(&asm.SubRegisterNumber{Destination: x86.SP, Source: x86.SP, Number: 32})
+				f.Assembler.Append(&asm.CallExtern{Library: fn.Package, Function: fn.Name})
+				f.Assembler.Append(&asm.MoveRegisterRegister{Destination: x86.SP, Source: x86.R5})
+			} else {
+				f.mv(instr.Arguments[1:], f.CPU.Call)
+				f.Assembler.Append(&asm.Call{Label: fn.UniqueName})
 			}
 
 		case *ssa.Syscall:

src/core/Evaluate.go

@@ -137,7 +137,12 @@ func (f *Function) Evaluate(expr *expression.Expression) (ssa.Value, error) {
 			return nil, errors.New(&UnknownIdentifier{Name: label}, f.File, left.Token.Position)
 		}
 
+		if function.IsExtern() {
+			f.Assembler.Libraries = f.Assembler.Libraries.Append(function.Package, function.Name)
+		} else {
 			f.Dependencies.Add(function)
+		}
+
 		v := f.AppendFunction(function.UniqueName, function.Type)
 		v.Source = ssa.Source(expr.Source)
 		return v, nil

src/core/Function.go

@@ -16,6 +16,7 @@ import (
 type Function struct {
 	ssa.IR
 	Name         string
+	Package      string
 	UniqueName   string
 	File         *fs.File
 	Input        []*ssa.Parameter
@@ -31,11 +32,12 @@ type Function struct {
 }
 
 // NewFunction creates a new function.
-func NewFunction(name string, file *fs.File) *Function {
+func NewFunction(name string, pkg string, file *fs.File) *Function {
 	return &Function{
 		Name:        name,
+		Package:     pkg,
+		UniqueName:  fmt.Sprintf("%s.%s", pkg, name),
 		File:        file,
-		UniqueName:  fmt.Sprintf("%s.%s", file.Package, name),
 		Identifiers: make(map[string]ssa.Value, 8),
 		IR: ssa.IR{
 			Blocks: []*ssa.Block{

src/cpu/CPU.go

@@ -4,4 +4,5 @@ package cpu
 type CPU struct {
 	Call       []Register
 	Syscall    []Register
+	ExternCall []Register
 }

src/dll/Library.go

@@ -0,0 +1,6 @@
+package dll
+
+type Library struct {
+	Name      string
+	Functions []string
+}

src/dll/List.go

@@ -0,0 +1,55 @@
+package dll
+
+import "slices"
+
+// List is a slice of DLLs.
+type List []Library
+
+// Append adds a function for the given DLL if it doesn't exist yet.
+func (list List) Append(dllName string, funcName string) List {
+	for i, dll := range list {
+		if dll.Name != dllName {
+			continue
+		}
+
+		if slices.Contains(dll.Functions, funcName) {
+			return list
+		}
+
+		list[i].Functions = append(list[i].Functions, funcName)
+		return list
+	}
+
+	return append(list, Library{Name: dllName, Functions: []string{funcName}})
+}
+
+// Contains returns true if the library exists.
+func (list List) Contains(dllName string) bool {
+	for _, dll := range list {
+		if dll.Name == dllName {
+			return true
+		}
+	}
+
+	return false
+}
+
+// Index returns the position of the given function name.
+func (list List) Index(dllName string, funcName string) int {
+	index := 0
+
+	for _, dll := range list {
+		if dll.Name != dllName {
+			index += len(dll.Functions) + 1
+			continue
+		}
+
+		for i, fn := range dll.Functions {
+			if fn == funcName {
+				return index + i
+			}
+		}
+	}
+
+	return -1
+}

src/dll/List_test.go

@@ -0,0 +1,34 @@
+package dll_test
+
+import (
+	"testing"
+
+	"git.urbach.dev/cli/q/src/dll"
+	"git.urbach.dev/go/assert"
+)
+
+func TestList(t *testing.T) {
+	libs := dll.List{}
+	assert.False(t, libs.Contains("kernel32"))
+	assert.Equal(t, -1, libs.Index("kernel32", "ExitProcess"))
+
+	libs = libs.Append("kernel32", "ExitProcess")
+	assert.True(t, libs.Contains("kernel32"))
+	assert.Equal(t, 0, libs.Index("kernel32", "ExitProcess"))
+
+	libs = libs.Append("user32", "MessageBox")
+	assert.True(t, libs.Contains("kernel32"))
+	assert.True(t, libs.Contains("user32"))
+	assert.Equal(t, 0, libs.Index("kernel32", "ExitProcess"))
+	assert.Equal(t, 2, libs.Index("user32", "MessageBox"))
+
+	libs = libs.Append("kernel32", "SetConsoleCP")
+	assert.Equal(t, 0, libs.Index("kernel32", "ExitProcess"))
+	assert.Equal(t, 1, libs.Index("kernel32", "SetConsoleCP"))
+	assert.Equal(t, 3, libs.Index("user32", "MessageBox"))
+
+	libs = libs.Append("kernel32", "ExitProcess")
+	assert.Equal(t, 0, libs.Index("kernel32", "ExitProcess"))
+	assert.Equal(t, 1, libs.Index("kernel32", "SetConsoleCP"))
+	assert.Equal(t, 3, libs.Index("user32", "MessageBox"))
+}

src/linker/WriteFile.go

@@ -9,6 +9,7 @@ import (
 	"git.urbach.dev/cli/q/src/data"
 	"git.urbach.dev/cli/q/src/elf"
 	"git.urbach.dev/cli/q/src/macho"
+	"git.urbach.dev/cli/q/src/pe"
 )
 
 // WriteFile writes an executable file to disk.
@@ -33,13 +34,15 @@ func WriteFile(executable string, b *build.Build, env *core.Environment) error {
 		final.Merge(&f.Assembler)
 	})
 
-	code, data := final.Compile(b)
+	code, data, libs := final.Compile(b)
 
 	switch b.OS {
 	case build.Linux:
 		elf.Write(file, b, code, data)
 	case build.Mac:
 		macho.Write(file, b, code, data)
+	case build.Windows:
+		pe.Write(file, b, code, data, libs)
 	}
 
 	err = file.Close()

src/pe/Arch.go

@@ -0,0 +1,23 @@
+package pe
+
+import (
+	"git.urbach.dev/cli/q/src/build"
+)
+
+const (
+	IMAGE_FILE_MACHINE_AMD64   = 0x8664
+	IMAGE_FILE_MACHINE_ARM64   = 0xAA64
+	IMAGE_FILE_MACHINE_RISCV64 = 0x5064
+)
+
+// Arch returns the CPU architecture used in the PE header.
+func Arch(arch build.Arch) uint16 {
+	switch arch {
+	case build.ARM:
+		return IMAGE_FILE_MACHINE_ARM64
+	case build.X86:
+		return IMAGE_FILE_MACHINE_AMD64
+	default:
+		return 0
+	}
+}

src/pe/Characteristics.go

@@ -0,0 +1,21 @@
+package pe
+
+type Characteristics uint16
+
+const (
+	IMAGE_FILE_RELOCS_STRIPPED         Characteristics = 0x0001
+	IMAGE_FILE_EXECUTABLE_IMAGE        Characteristics = 0x0002
+	IMAGE_FILE_LINE_NUMS_STRIPPED      Characteristics = 0x0004
+	IMAGE_FILE_LOCAL_SYMS_STRIPPED     Characteristics = 0x0008
+	IMAGE_FILE_AGGRESSIVE_WS_TRIM      Characteristics = 0x0010
+	IMAGE_FILE_LARGE_ADDRESS_AWARE     Characteristics = 0x0020
+	IMAGE_FILE_BYTES_REVERSED_LO       Characteristics = 0x0080
+	IMAGE_FILE_32BIT_MACHINE           Characteristics = 0x0100
+	IMAGE_FILE_DEBUG_STRIPPED          Characteristics = 0x0200
+	IMAGE_FILE_REMOVABLE_RUN_FROM_SWAP Characteristics = 0x0400
+	IMAGE_FILE_NET_RUN_FROM_SWAP       Characteristics = 0x0800
+	IMAGE_FILE_SYSTEM                  Characteristics = 0x1000
+	IMAGE_FILE_DLL                     Characteristics = 0x2000
+	IMAGE_FILE_UP_SYSTEM_ONLY          Characteristics = 0x4000
+	IMAGE_FILE_BYTES_REVERSED_HI       Characteristics = 0x8000
+)

src/pe/Constants.go

@@ -0,0 +1,7 @@
+package pe
+
+const (
+	BaseAddress = 0x400000
+	NumSections = 3
+	HeaderEnd   = DOSHeaderSize + NTHeaderSize + OptionalHeader64Size + SectionHeaderSize*NumSections
+)

src/pe/DLLImport.go

@@ -0,0 +1,11 @@
+package pe
+
+const DLLImportSize = 20
+
+type DLLImport struct {
+	RvaFunctionNameList    uint32
+	TimeDateStamp          uint32
+	ForwarderChain         uint32
+	RvaModuleName          uint32
+	RvaFunctionAddressList uint32
+}

src/pe/DOSHeader.go

@@ -0,0 +1,11 @@
+package pe
+
+const DOSHeaderSize = 64
+
+// DOSHeader is at the beginning of each EXE file and nowadays just points
+// to the PEHeader using an absolute file offset.
+type DOSHeader struct {
+	Magic          [4]byte
+	_              [56]byte
+	NTHeaderOffset uint32
+}

src/pe/DataDirectory.go

@@ -0,0 +1,6 @@
+package pe
+
+type DataDirectory struct {
+	VirtualAddress uint32
+	Size           uint32
+}

src/pe/DllCharacteristics.go

@@ -0,0 +1,17 @@
+package pe
+
+type DllCharacteristics uint16
+
+const (
+	IMAGE_DLLCHARACTERISTICS_HIGH_ENTROPY_VA       DllCharacteristics = 0x0020
+	IMAGE_DLLCHARACTERISTICS_DYNAMIC_BASE          DllCharacteristics = 0x0040
+	IMAGE_DLLCHARACTERISTICS_FORCE_INTEGRITY       DllCharacteristics = 0x0080
+	IMAGE_DLLCHARACTERISTICS_NX_COMPAT             DllCharacteristics = 0x0100
+	IMAGE_DLLCHARACTERISTICS_NO_ISOLATION          DllCharacteristics = 0x0200
+	IMAGE_DLLCHARACTERISTICS_NO_SEH                DllCharacteristics = 0x0400
+	IMAGE_DLLCHARACTERISTICS_NO_BIND               DllCharacteristics = 0x0800
+	IMAGE_DLLCHARACTERISTICS_APPCONTAINER          DllCharacteristics = 0x1000
+	IMAGE_DLLCHARACTERISTICS_WDM_DRIVER            DllCharacteristics = 0x2000
+	IMAGE_DLLCHARACTERISTICS_GUARD_CF              DllCharacteristics = 0x4000
+	IMAGE_DLLCHARACTERISTICS_TERMINAL_SERVER_AWARE DllCharacteristics = 0x8000
+)

src/pe/EXE.go

@@ -0,0 +1,147 @@
+package pe
+
+import (
+	"bytes"
+	"encoding/binary"
+	"io"
+
+	"git.urbach.dev/cli/q/src/build"
+	"git.urbach.dev/cli/q/src/dll"
+	"git.urbach.dev/cli/q/src/exe"
+)
+
+// EXE is the portable executable format used on Windows.
+type EXE struct {
+	DOSHeader
+	NTHeader
+	OptionalHeader64
+	Sections []SectionHeader
+}
+
+// Write writes the EXE file to the given writer.
+func Write(writer io.WriteSeeker, b *build.Build, codeBytes []byte, dataBytes []byte, libs dll.List) {
+	x := exe.New(HeaderEnd, b.FileAlign, b.MemoryAlign)
+	x.InitSections(codeBytes, dataBytes, nil)
+	code := x.Sections[0]
+	data := x.Sections[1]
+	imports := x.Sections[2]
+	subSystem := IMAGE_SUBSYSTEM_WINDOWS_CUI
+	arch := Arch(b.Arch)
+
+	importsData, dllData, dllImports, dllDataStart := importLibraries(libs, imports.FileOffset)
+	buffer := bytes.Buffer{}
+	binary.Write(&buffer, binary.LittleEndian, &importsData)
+	binary.Write(&buffer, binary.LittleEndian, &dllData)
+	binary.Write(&buffer, binary.LittleEndian, &dllImports)
+	imports.Bytes = buffer.Bytes()
+	importDirectoryStart := dllDataStart + len(dllData)
+	importDirectorySize := DLLImportSize * len(dllImports)
+	imageSize := exe.Align(imports.MemoryOffset+len(imports.Bytes), b.MemoryAlign)
+
+	if libs.Contains("user32") {
+		subSystem = IMAGE_SUBSYSTEM_WINDOWS_GUI
+	}
+
+	pe := &EXE{
+		DOSHeader: DOSHeader{
+			Magic:          [4]byte{'M', 'Z', 0, 0},
+			NTHeaderOffset: DOSHeaderSize,
+		},
+		NTHeader: NTHeader{
+			Signature:            [4]byte{'P', 'E', 0, 0},
+			Machine:              arch,
+			NumberOfSections:     uint16(NumSections),
+			TimeDateStamp:        0,
+			PointerToSymbolTable: 0,
+			NumberOfSymbols:      0,
+			SizeOfOptionalHeader: OptionalHeader64Size,
+			Characteristics:      IMAGE_FILE_EXECUTABLE_IMAGE | IMAGE_FILE_LARGE_ADDRESS_AWARE,
+		},
+		OptionalHeader64: OptionalHeader64{
+			Magic:                       0x020B, // PE32+ / 64-bit executable
+			MajorLinkerVersion:          0x0E,
+			MinorLinkerVersion:          0x16,
+			SizeOfCode:                  uint32(len(code.Bytes)),
+			SizeOfInitializedData:       0,
+			SizeOfUninitializedData:     0,
+			AddressOfEntryPoint:         uint32(code.MemoryOffset),
+			BaseOfCode:                  uint32(code.MemoryOffset),
+			ImageBase:                   BaseAddress,
+			SectionAlignment:            uint32(b.MemoryAlign), // power of 2, must be greater than or equal to FileAlignment
+			FileAlignment:               uint32(b.FileAlign),   // power of 2
+			MajorOperatingSystemVersion: 0x06,
+			MinorOperatingSystemVersion: 0,
+			MajorImageVersion:           0,
+			MinorImageVersion:           0,
+			MajorSubsystemVersion:       0x06,
+			MinorSubsystemVersion:       0,
+			Win32VersionValue:           0,
+			SizeOfImage:                 uint32(imageSize),       // a multiple of SectionAlignment
+			SizeOfHeaders:               uint32(code.FileOffset), // section bodies begin here
+			CheckSum:                    0,
+			Subsystem:                   subSystem,
+			DllCharacteristics:          IMAGE_DLLCHARACTERISTICS_HIGH_ENTROPY_VA | IMAGE_DLLCHARACTERISTICS_DYNAMIC_BASE | IMAGE_DLLCHARACTERISTICS_NX_COMPAT | IMAGE_DLLCHARACTERISTICS_TERMINAL_SERVER_AWARE,
+			SizeOfStackReserve:          0x100000,
+			SizeOfStackCommit:           0x1000,
+			SizeOfHeapReserve:           0x100000,
+			SizeOfHeapCommit:            0x1000,
+			LoaderFlags:                 0,
+			NumberOfRvaAndSizes:         16,
+			DataDirectory: [16]DataDirectory{
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: uint32(importDirectoryStart), Size: uint32(importDirectorySize)}, // RVA of the imported function table
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: uint32(imports.MemoryOffset), Size: uint32(len(importsData) * 8)}, // RVA of the import address table
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+				{VirtualAddress: 0, Size: 0},
+			},
+		},
+		Sections: []SectionHeader{
+			{
+				Name:            [8]byte{'.', 't', 'e', 'x', 't'},
+				VirtualSize:     uint32(len(code.Bytes)),
+				VirtualAddress:  uint32(code.MemoryOffset),
+				RawSize:         uint32(len(code.Bytes)), // must be a multiple of FileAlignment
+				RawAddress:      uint32(code.FileOffset), // must be a multiple of FileAlignment
+				Characteristics: IMAGE_SCN_CNT_CODE | IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_READ,
+			},
+			{
+				Name:            [8]byte{'.', 'r', 'd', 'a', 't', 'a'},
+				VirtualSize:     uint32(len(data.Bytes)),
+				VirtualAddress:  uint32(data.MemoryOffset),
+				RawSize:         uint32(len(data.Bytes)),
+				RawAddress:      uint32(data.FileOffset),
+				Characteristics: IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ,
+			},
+			{
+				Name:            [8]byte{'.', 'i', 'd', 'a', 't', 'a'},
+				VirtualSize:     uint32(len(imports.Bytes)),
+				VirtualAddress:  uint32(imports.MemoryOffset),
+				RawSize:         uint32(len(imports.Bytes)),
+				RawAddress:      uint32(imports.FileOffset),
+				Characteristics: IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ,
+			},
+		},
+	}
+
+	binary.Write(writer, binary.LittleEndian, &pe.DOSHeader)
+	binary.Write(writer, binary.LittleEndian, &pe.NTHeader)
+	binary.Write(writer, binary.LittleEndian, &pe.OptionalHeader64)
+	binary.Write(writer, binary.LittleEndian, &pe.Sections)
+	writer.Seek(int64(code.Padding), io.SeekCurrent)
+	writer.Write(code.Bytes)
+	writer.Seek(int64(data.Padding), io.SeekCurrent)
+	writer.Write(data.Bytes)
+	writer.Seek(int64(imports.Padding), io.SeekCurrent)
+	writer.Write(imports.Bytes)
+}

src/pe/EXE_test.go

@@ -0,0 +1,15 @@
+package pe_test
+
+import (
+	"testing"
+
+	"git.urbach.dev/cli/q/src/build"
+	"git.urbach.dev/cli/q/src/exe"
+	"git.urbach.dev/cli/q/src/pe"
+)
+
+func TestWrite(t *testing.T) {
+	pe.Write(&exe.Discard{}, &build.Build{Arch: build.ARM, FileAlign: 0x4000, MemoryAlign: 0x4000}, nil, nil, nil)
+	pe.Write(&exe.Discard{}, &build.Build{Arch: build.X86, FileAlign: 0x1000, MemoryAlign: 0x1000}, nil, nil, nil)
+	pe.Write(&exe.Discard{}, &build.Build{Arch: build.UnknownArch, FileAlign: 0x1000, MemoryAlign: 0x1000}, nil, nil, nil)
+}

src/pe/NTHeader.go

@@ -0,0 +1,14 @@
+package pe
+
+const NTHeaderSize = 24
+
+type NTHeader struct {
+	Signature            [4]byte
+	Machine              uint16
+	NumberOfSections     uint16
+	TimeDateStamp        uint32
+	PointerToSymbolTable uint32
+	NumberOfSymbols      uint32
+	SizeOfOptionalHeader uint16
+	Characteristics      Characteristics
+}

src/pe/OptionalHeader64.go

@@ -0,0 +1,36 @@
+package pe
+
+const OptionalHeader64Size = 240
+
+type OptionalHeader64 struct {
+	Magic                       uint16
+	MajorLinkerVersion          uint8
+	MinorLinkerVersion          uint8
+	SizeOfCode                  uint32
+	SizeOfInitializedData       uint32
+	SizeOfUninitializedData     uint32
+	AddressOfEntryPoint         uint32
+	BaseOfCode                  uint32
+	ImageBase                   uint64
+	SectionAlignment            uint32
+	FileAlignment               uint32
+	MajorOperatingSystemVersion uint16
+	MinorOperatingSystemVersion uint16
+	MajorImageVersion           uint16
+	MinorImageVersion           uint16
+	MajorSubsystemVersion       uint16
+	MinorSubsystemVersion       uint16
+	Win32VersionValue           uint32
+	SizeOfImage                 uint32
+	SizeOfHeaders               uint32
+	CheckSum                    uint32
+	Subsystem                   Subsystem
+	DllCharacteristics          DllCharacteristics
+	SizeOfStackReserve          uint64
+	SizeOfStackCommit           uint64
+	SizeOfHeapReserve           uint64
+	SizeOfHeapCommit            uint64
+	LoaderFlags                 uint32
+	NumberOfRvaAndSizes         uint32
+	DataDirectory               [16]DataDirectory
+}

src/pe/SectionCharacteristics.go

@@ -0,0 +1,14 @@
+package pe
+
+type SectionCharacteristics uint32
+
+const (
+	IMAGE_SCN_CNT_CODE               SectionCharacteristics = 0x00000020
+	IMAGE_SCN_CNT_INITIALIZED_DATA   SectionCharacteristics = 0x00000040
+	IMAGE_SCN_CNT_UNINITIALIZED_DATA SectionCharacteristics = 0x00000080
+	IMAGE_SCN_LNK_COMDAT             SectionCharacteristics = 0x00001000
+	IMAGE_SCN_MEM_DISCARDABLE        SectionCharacteristics = 0x02000000
+	IMAGE_SCN_MEM_EXECUTE            SectionCharacteristics = 0x20000000
+	IMAGE_SCN_MEM_READ               SectionCharacteristics = 0x40000000
+	IMAGE_SCN_MEM_WRITE              SectionCharacteristics = 0x80000000
+)

src/pe/SectionHeader.go

@@ -0,0 +1,16 @@
+package pe
+
+const SectionHeaderSize = 40
+
+type SectionHeader struct {
+	Name                 [8]byte
+	VirtualSize          uint32
+	VirtualAddress       uint32
+	RawSize              uint32
+	RawAddress           uint32
+	PointerToRelocations uint32
+	PointerToLineNumbers uint32
+	NumberOfRelocations  uint16
+	NumberOfLineNumbers  uint16
+	Characteristics      SectionCharacteristics
+}

src/pe/Subsystem.go

@@ -0,0 +1,20 @@
+package pe
+
+type Subsystem uint16
+
+const (
+	IMAGE_SUBSYSTEM_UNKNOWN                  Subsystem = 0
+	IMAGE_SUBSYSTEM_NATIVE                   Subsystem = 1
+	IMAGE_SUBSYSTEM_WINDOWS_GUI              Subsystem = 2
+	IMAGE_SUBSYSTEM_WINDOWS_CUI              Subsystem = 3
+	IMAGE_SUBSYSTEM_OS2_CUI                  Subsystem = 5
+	IMAGE_SUBSYSTEM_POSIX_CUI                Subsystem = 7
+	IMAGE_SUBSYSTEM_NATIVE_WINDOWS           Subsystem = 8
+	IMAGE_SUBSYSTEM_WINDOWS_CE_GUI           Subsystem = 9
+	IMAGE_SUBSYSTEM_EFI_APPLICATION          Subsystem = 10
+	IMAGE_SUBSYSTEM_EFI_BOOT_SERVICE_DRIVER  Subsystem = 11
+	IMAGE_SUBSYSTEM_EFI_RUNTIME_DRIVER       Subsystem = 12
+	IMAGE_SUBSYSTEM_EFI_ROM                  Subsystem = 13
+	IMAGE_SUBSYSTEM_XBOX                     Subsystem = 14
+	IMAGE_SUBSYSTEM_WINDOWS_BOOT_APPLICATION Subsystem = 16
+)

src/pe/importLibraries.go

@@ -0,0 +1,60 @@
+package pe
+
+import "git.urbach.dev/cli/q/src/dll"
+
+// importLibraries generates the import address table which contains the addresses of functions imported from DLLs.
+func importLibraries(dlls dll.List, importsStart int) ([]uint64, []byte, []DLLImport, int) {
+	imports := make([]uint64, 0)
+	dllData := make([]byte, 0)
+	dllImports := []DLLImport{}
+
+	for _, library := range dlls {
+		functionsStart := len(imports) * 8
+		dllNamePos := len(dllData)
+		dllData = append(dllData, library.Name...)
+		dllData = append(dllData, ".dll"...)
+		dllData = append(dllData, 0x00)
+
+		dllImports = append(dllImports, DLLImport{
+			RvaFunctionNameList:    uint32(importsStart + functionsStart),
+			TimeDateStamp:          0,
+			ForwarderChain:         0,
+			RvaModuleName:          uint32(dllNamePos),
+			RvaFunctionAddressList: uint32(importsStart + functionsStart),
+		})
+
+		for _, fn := range library.Functions {
+			if len(dllData)&1 != 0 {
+				dllData = append(dllData, 0x00) // align the next entry on an even boundary
+			}
+
+			offset := len(dllData)
+			dllData = append(dllData, 0x00, 0x00)
+			dllData = append(dllData, fn...)
+			dllData = append(dllData, 0x00)
+
+			imports = append(imports, uint64(offset))
+		}
+
+		imports = append(imports, 0)
+	}
+
+	dllDataStart := importsStart + len(imports)*8
+
+	for i := range imports {
+		if imports[i] == 0 {
+			continue
+		}
+
+		imports[i] += uint64(dllDataStart)
+	}
+
+	for i := range dllImports {
+		dllImports[i].RvaModuleName += uint32(dllDataStart)
+	}
+
+	// a zeroed structure marks the end of the list
+	dllImports = append(dllImports, DLLImport{})
+
+	return imports, dllData, dllImports, dllDataStart
+}

src/scanner/scanExtern.go

@@ -0,0 +1,68 @@
+package scanner
+
+import (
+	"git.urbach.dev/cli/q/src/errors"
+	"git.urbach.dev/cli/q/src/fs"
+	"git.urbach.dev/cli/q/src/token"
+)
+
+// scanExtern scans a block of external libraries.
+func (s *scanner) scanExtern(file *fs.File, tokens token.List, i int) (int, error) {
+	i++
+
+	if tokens[i].Kind != token.BlockStart {
+		return i, errors.New(MissingBlockStart, file, tokens[i].Position)
+	}
+
+	for i < len(tokens) {
+		switch tokens[i].Kind {
+		case token.Identifier:
+			var err error
+			i, err = s.scanExternLibrary(file, tokens, i)
+
+			if err != nil {
+				return i, err
+			}
+
+		case token.BlockEnd:
+			return i, nil
+		}
+
+		i++
+	}
+
+	return i, errors.New(MissingBlockEnd, file, tokens[i].Position)
+}
+
+// scanExternLibrary scans a block of external function declarations.
+func (s *scanner) scanExternLibrary(file *fs.File, tokens token.List, i int) (int, error) {
+	dllName := tokens[i].String(file.Bytes)
+	i++
+
+	if tokens[i].Kind != token.BlockStart {
+		return i, errors.New(MissingBlockStart, file, tokens[i].Position)
+	}
+
+	i++
+
+	for i < len(tokens) {
+		switch tokens[i].Kind {
+		case token.Identifier:
+			function, j, err := scanSignature(file, dllName, tokens, i, token.NewLine)
+
+			if err != nil {
+				return j, err
+			}
+
+			i = j
+			s.functions <- function
+
+		case token.BlockEnd:
+			return i, nil
+		}
+
+		i++
+	}
+
+	return i, errors.New(MissingBlockEnd, file, tokens[i].Position)
+}

src/scanner/scanFile.go

@@ -33,6 +33,8 @@ func (s *scanner) scanFile(path string, pkg string) error {
 		case token.Comment:
 		case token.Identifier:
 			i, err = s.scanFunction(file, tokens, i)
+		case token.Extern:
+			i, err = s.scanExtern(file, tokens, i)
 		case token.Import:
 			i, err = s.scanImport(file, tokens, i)
 		case token.EOF:

src/scanner/scanFunction.go

@@ -11,7 +11,7 @@ import (
 
 // scanFunction scans a function.
 func (s *scanner) scanFunction(file *fs.File, tokens token.List, i int) (int, error) {
-	function, i, err := scanSignature(file, tokens, i, token.BlockStart)
+	function, i, err := scanSignature(file, file.Package, tokens, i, token.BlockStart)
 
 	if err != nil {
 		return i, err

src/scanner/scanSignature.go

@@ -9,7 +9,7 @@ import (
 )
 
 // scanSignature scans only the function signature without the body.
-func scanSignature(file *fs.File, tokens token.List, i int, delimiter token.Kind) (*core.Function, int, error) {
+func scanSignature(file *fs.File, pkg string, tokens token.List, i int, delimiter token.Kind) (*core.Function, int, error) {
 	var (
 		groupLevel  = 0
 		nameStart   = i
@@ -83,7 +83,7 @@ func scanSignature(file *fs.File, tokens token.List, i int, delimiter token.Kind
 	}
 
 	name := tokens[nameStart].String(file.Bytes)
-	function := core.NewFunction(name, file)
+	function := core.NewFunction(name, pkg, file)
 	parameters := tokens[inputStart:inputEnd]
 
 	for param := range parameters.Split {

src/x86/Registers.go

@@ -24,4 +24,5 @@ const (
 var CPU = cpu.CPU{
 	Call:       []cpu.Register{R0, R7, R6, R2, R10, R8, R9},
 	Syscall:    []cpu.Register{R0, R7, R6, R2, R10, R8, R9},
+	ExternCall: []cpu.Register{R1, R2, R8, R9},
 }