src/cmd/link/internal/ld/pe.go

// Copyright 2009 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.

// PE (Portable Executable) file writing
// https://www.microsoft.com/whdc/system/platform/firmware/PECOFF.mspx

package ld

import (
	"cmd/internal/objabi"
	"cmd/internal/sys"
	"cmd/link/internal/loader"
	"cmd/link/internal/sym"
	"debug/pe"
	"encoding/binary"
	"fmt"
	"sort"
	"strconv"
	"strings"
)

type IMAGE_IMPORT_DESCRIPTOR struct {
	OriginalFirstThunk uint32
	TimeDateStamp      uint32
	ForwarderChain     uint32
	Name               uint32
	FirstThunk         uint32
}

type IMAGE_EXPORT_DIRECTORY struct {
	Characteristics       uint32
	TimeDateStamp         uint32
	MajorVersion          uint16
	MinorVersion          uint16
	Name                  uint32
	Base                  uint32
	NumberOfFunctions     uint32
	NumberOfNames         uint32
	AddressOfFunctions    uint32
	AddressOfNames        uint32
	AddressOfNameOrdinals uint32
}

var (
	// PEBASE is the base address for the executable.
	// It is small for 32-bit and large for 64-bit.
	PEBASE int64

	// SectionAlignment must be greater than or equal to FileAlignment.
	// The default is the page size for the architecture.
	PESECTALIGN int64 = 0x1000

	// FileAlignment should be a power of 2 between 512 and 64 K, inclusive.
	// The default is 512. If the SectionAlignment is less than
	// the architecture's page size, then FileAlignment must match SectionAlignment.
	PEFILEALIGN int64 = 2 << 8
)

const (
	IMAGE_SCN_CNT_CODE               = 0x00000020
	IMAGE_SCN_CNT_INITIALIZED_DATA   = 0x00000040
	IMAGE_SCN_CNT_UNINITIALIZED_DATA = 0x00000080
	IMAGE_SCN_MEM_EXECUTE            = 0x20000000
	IMAGE_SCN_MEM_READ               = 0x40000000
	IMAGE_SCN_MEM_WRITE              = 0x80000000
	IMAGE_SCN_MEM_DISCARDABLE        = 0x2000000
	IMAGE_SCN_LNK_NRELOC_OVFL        = 0x1000000
	IMAGE_SCN_ALIGN_4BYTES           = 0x300000
	IMAGE_SCN_ALIGN_8BYTES           = 0x400000
	IMAGE_SCN_ALIGN_32BYTES          = 0x600000
)

// See https://docs.microsoft.com/en-us/windows/win32/debug/pe-format.
// TODO(crawshaw): add these constants to debug/pe.
const (
	// TODO: the Microsoft doco says IMAGE_SYM_DTYPE_ARRAY is 3 and IMAGE_SYM_DTYPE_FUNCTION is 2
	IMAGE_SYM_TYPE_NULL      = 0
	IMAGE_SYM_TYPE_STRUCT    = 8
	IMAGE_SYM_DTYPE_FUNCTION = 0x20
	IMAGE_SYM_DTYPE_ARRAY    = 0x30
	IMAGE_SYM_CLASS_EXTERNAL = 2
	IMAGE_SYM_CLASS_STATIC   = 3

	IMAGE_REL_I386_DIR32  = 0x0006
	IMAGE_REL_I386_SECREL = 0x000B
	IMAGE_REL_I386_REL32  = 0x0014

	IMAGE_REL_AMD64_ADDR64 = 0x0001
	IMAGE_REL_AMD64_ADDR32 = 0x0002
	IMAGE_REL_AMD64_REL32  = 0x0004
	IMAGE_REL_AMD64_SECREL = 0x000B

	IMAGE_REL_ARM_ABSOLUTE = 0x0000
	IMAGE_REL_ARM_ADDR32   = 0x0001
	IMAGE_REL_ARM_ADDR32NB = 0x0002
	IMAGE_REL_ARM_BRANCH24 = 0x0003
	IMAGE_REL_ARM_BRANCH11 = 0x0004
	IMAGE_REL_ARM_SECREL   = 0x000F

	IMAGE_REL_ARM64_ABSOLUTE       = 0x0000
	IMAGE_REL_ARM64_ADDR32         = 0x0001
	IMAGE_REL_ARM64_ADDR32NB       = 0x0002
	IMAGE_REL_ARM64_BRANCH26       = 0x0003
	IMAGE_REL_ARM64_PAGEBASE_REL21 = 0x0004
	IMAGE_REL_ARM64_REL21          = 0x0005
	IMAGE_REL_ARM64_PAGEOFFSET_12A = 0x0006
	IMAGE_REL_ARM64_PAGEOFFSET_12L = 0x0007
	IMAGE_REL_ARM64_SECREL         = 0x0008
	IMAGE_REL_ARM64_SECREL_LOW12A  = 0x0009
	IMAGE_REL_ARM64_SECREL_HIGH12A = 0x000A
	IMAGE_REL_ARM64_SECREL_LOW12L  = 0x000B
	IMAGE_REL_ARM64_TOKEN          = 0x000C
	IMAGE_REL_ARM64_SECTION        = 0x000D
	IMAGE_REL_ARM64_ADDR64         = 0x000E
	IMAGE_REL_ARM64_BRANCH19       = 0x000F
	IMAGE_REL_ARM64_BRANCH14       = 0x0010
	IMAGE_REL_ARM64_REL32          = 0x0011

	IMAGE_REL_BASED_HIGHLOW = 3
	IMAGE_REL_BASED_DIR64   = 10
)

const (
	PeMinimumTargetMajorVersion = 6
	PeMinimumTargetMinorVersion = 1
)

// DOS stub that prints out
// "This program cannot be run in DOS mode."
var dosstub = []uint8{
	0x4d,
	0x5a,
	0x90,
	0x00,
	0x03,
	0x00,
	0x04,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0xff,
	0xff,
	0x00,
	0x00,
	0x8b,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x40,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x80,
	0x00,
	0x00,
	0x00,
	0x0e,
	0x1f,
	0xba,
	0x0e,
	0x00,
	0xb4,
	0x09,
	0xcd,
	0x21,
	0xb8,
	0x01,
	0x4c,
	0xcd,
	0x21,
	0x54,
	0x68,
	0x69,
	0x73,
	0x20,
	0x70,
	0x72,
	0x6f,
	0x67,
	0x72,
	0x61,
	0x6d,
	0x20,
	0x63,
	0x61,
	0x6e,
	0x6e,
	0x6f,
	0x74,
	0x20,
	0x62,
	0x65,
	0x20,
	0x72,
	0x75,
	0x6e,
	0x20,
	0x69,
	0x6e,
	0x20,
	0x44,
	0x4f,
	0x53,
	0x20,
	0x6d,
	0x6f,
	0x64,
	0x65,
	0x2e,
	0x0d,
	0x0d,
	0x0a,
	0x24,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
	0x00,
}

type Imp struct {
	s       loader.Sym
	off     uint64
	next    *Imp
	argsize int
}

type Dll struct {
	name     string
	nameoff  uint64
	thunkoff uint64
	ms       *Imp
	next     *Dll
}

var (
	rsrcsyms    []loader.Sym
	PESECTHEADR int32
	PEFILEHEADR int32
	pe64        int
	dr          *Dll

	dexport = make([]loader.Sym, 0, 1024)
)

// peStringTable is a COFF string table.
type peStringTable struct {
	strings    []string
	stringsLen int
}

// size returns size of string table t.
func (t *peStringTable) size() int {
	// string table starts with 4-byte length at the beginning
	return t.stringsLen + 4
}

// add adds string str to string table t.
func (t *peStringTable) add(str string) int {
	off := t.size()
	t.strings = append(t.strings, str)
	t.stringsLen += len(str) + 1 // each string will have 0 appended to it
	return off
}

// write writes string table t into the output file.
func (t *peStringTable) write(out *OutBuf) {
	out.Write32(uint32(t.size()))
	for _, s := range t.strings {
		out.WriteString(s)
		out.Write8(0)
	}
}

// peSection represents section from COFF section table.
type peSection struct {
	name                 string
	shortName            string
	index                int // one-based index into the Section Table
	virtualSize          uint32
	virtualAddress       uint32
	sizeOfRawData        uint32
	pointerToRawData     uint32
	pointerToRelocations uint32
	numberOfRelocations  uint16
	characteristics      uint32
}

// checkOffset verifies COFF section sect offset in the file.
func (sect *peSection) checkOffset(off int64) {
	if off != int64(sect.pointerToRawData) {
		Errorf(nil, "%s.PointerToRawData = %#x, want %#x", sect.name, uint64(int64(sect.pointerToRawData)), uint64(off))
		errorexit()
	}
}

// checkSegment verifies COFF section sect matches address
// and file offset provided in segment seg.
func (sect *peSection) checkSegment(seg *sym.Segment) {
	if seg.Vaddr-uint64(PEBASE) != uint64(sect.virtualAddress) {
		Errorf(nil, "%s.VirtualAddress = %#x, want %#x", sect.name, uint64(int64(sect.virtualAddress)), uint64(int64(seg.Vaddr-uint64(PEBASE))))
		errorexit()
	}
	if seg.Fileoff != uint64(sect.pointerToRawData) {
		Errorf(nil, "%s.PointerToRawData = %#x, want %#x", sect.name, uint64(int64(sect.pointerToRawData)), uint64(int64(seg.Fileoff)))
		errorexit()
	}
}

// pad adds zeros to the section sect. It writes as many bytes
// as necessary to make section sect.SizeOfRawData bytes long.
// It assumes that n bytes are already written to the file.
func (sect *peSection) pad(out *OutBuf, n uint32) {
	out.WriteStringN("", int(sect.sizeOfRawData-n))
}

// write writes COFF section sect into the output file.
func (sect *peSection) write(out *OutBuf, linkmode LinkMode) error {
	h := pe.SectionHeader32{
		VirtualSize:          sect.virtualSize,
		SizeOfRawData:        sect.sizeOfRawData,
		PointerToRawData:     sect.pointerToRawData,
		PointerToRelocations: sect.pointerToRelocations,
		NumberOfRelocations:  sect.numberOfRelocations,
		Characteristics:      sect.characteristics,
	}
	if linkmode != LinkExternal {
		h.VirtualAddress = sect.virtualAddress
	}
	copy(h.Name[:], sect.shortName)
	return binary.Write(out, binary.LittleEndian, h)
}

// emitRelocations emits the relocation entries for the sect.
// The actual relocations are emitted by relocfn.
// This updates the corresponding PE section table entry
// with the relocation offset and count.
func (sect *peSection) emitRelocations(out *OutBuf, relocfn func() int) {
	sect.pointerToRelocations = uint32(out.Offset())
	// first entry: extended relocs
	out.Write32(0) // placeholder for number of relocation + 1
	out.Write32(0)
	out.Write16(0)

	n := relocfn() + 1

	cpos := out.Offset()
	out.SeekSet(int64(sect.pointerToRelocations))
	out.Write32(uint32(n))
	out.SeekSet(cpos)
	if n > 0x10000 {
		n = 0x10000
		sect.characteristics |= IMAGE_SCN_LNK_NRELOC_OVFL
	} else {
		sect.pointerToRelocations += 10 // skip the extend reloc entry
	}
	sect.numberOfRelocations = uint16(n - 1)
}

// peFile is used to build COFF file.
type peFile struct {
	sections       []*peSection
	stringTable    peStringTable
	textSect       *peSection
	rdataSect      *peSection
	dataSect       *peSection
	bssSect        *peSection
	ctorsSect      *peSection
	nextSectOffset uint32
	nextFileOffset uint32
	symtabOffset   int64 // offset to the start of symbol table
	symbolCount    int   // number of symbol table records written
	dataDirectory  [16]pe.DataDirectory
}

// addSection adds section to the COFF file f.
func (f *peFile) addSection(name string, sectsize int, filesize int) *peSection {
	sect := &peSection{
		name:             name,
		shortName:        name,
		index:            len(f.sections) + 1,
		virtualAddress:   f.nextSectOffset,
		pointerToRawData: f.nextFileOffset,
	}
	f.nextSectOffset = uint32(Rnd(int64(f.nextSectOffset)+int64(sectsize), PESECTALIGN))
	if filesize > 0 {
		sect.virtualSize = uint32(sectsize)
		sect.sizeOfRawData = uint32(Rnd(int64(filesize), PEFILEALIGN))
		f.nextFileOffset += sect.sizeOfRawData
	} else {
		sect.sizeOfRawData = uint32(sectsize)
	}
	f.sections = append(f.sections, sect)
	return sect
}

// addDWARFSection adds DWARF section to the COFF file f.
// This function is similar to addSection, but DWARF section names are
// longer than 8 characters, so they need to be stored in the string table.
func (f *peFile) addDWARFSection(name string, size int) *peSection {
	if size == 0 {
		Exitf("DWARF section %q is empty", name)
	}
	// DWARF section names are longer than 8 characters.
	// PE format requires such names to be stored in string table,
	// and section names replaced with slash (/) followed by
	// correspondent string table index.
	// see http://www.microsoft.com/whdc/system/platform/firmware/PECOFFdwn.mspx
	// for details
	off := f.stringTable.add(name)
	h := f.addSection(name, size, size)
	h.shortName = fmt.Sprintf("/%d", off)
	h.characteristics = IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_DISCARDABLE
	return h
}

// addDWARF adds DWARF information to the COFF file f.
func (f *peFile) addDWARF() {
	if *FlagS { // disable symbol table
		return
	}
	if *FlagW { // disable dwarf
		return
	}
	for _, sect := range Segdwarf.Sections {
		h := f.addDWARFSection(sect.Name, int(sect.Length))
		fileoff := sect.Vaddr - Segdwarf.Vaddr + Segdwarf.Fileoff
		if uint64(h.pointerToRawData) != fileoff {
			Exitf("%s.PointerToRawData = %#x, want %#x", sect.Name, h.pointerToRawData, fileoff)
		}
	}
}

// addInitArray adds .ctors COFF section to the file f.
func (f *peFile) addInitArray(ctxt *Link) *peSection {
	// The size below was determined by the specification for array relocations,
	// and by observing what GCC writes here. If the initarray section grows to
	// contain more than one constructor entry, the size will need to be 8 * constructor_count.
	// However, the entire Go runtime is initialized from just one function, so it is unlikely
	// that this will need to grow in the future.
	var size int
	var alignment uint32
	switch objabi.GOARCH {
	default:
		Exitf("peFile.addInitArray: unsupported GOARCH=%q\n", objabi.GOARCH)
	case "386", "arm":
		size = 4
		alignment = IMAGE_SCN_ALIGN_4BYTES
	case "amd64", "arm64":
		size = 8
		alignment = IMAGE_SCN_ALIGN_8BYTES
	}
	sect := f.addSection(".ctors", size, size)
	sect.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | alignment
	sect.sizeOfRawData = uint32(size)
	ctxt.Out.SeekSet(int64(sect.pointerToRawData))
	sect.checkOffset(ctxt.Out.Offset())

	init_entry := ctxt.loader.Lookup(*flagEntrySymbol, 0)
	addr := uint64(ctxt.loader.SymValue(init_entry)) - ctxt.loader.SymSect(init_entry).Vaddr
	switch objabi.GOARCH {
	case "386", "arm":
		ctxt.Out.Write32(uint32(addr))
	case "amd64", "arm64":
		ctxt.Out.Write64(addr)
	}
	return sect
}

// emitRelocations emits relocation entries for go.o in external linking.
func (f *peFile) emitRelocations(ctxt *Link) {
	for ctxt.Out.Offset()&7 != 0 {
		ctxt.Out.Write8(0)
	}

	ldr := ctxt.loader

	// relocsect relocates symbols from first in section sect, and returns
	// the total number of relocations emitted.
	relocsect := func(sect *sym.Section, syms []loader.Sym, base uint64) int {
		// If main section has no bits, nothing to relocate.
		if sect.Vaddr >= sect.Seg.Vaddr+sect.Seg.Filelen {
			return 0
		}
		nrelocs := 0
		sect.Reloff = uint64(ctxt.Out.Offset())
		for i, s := range syms {
			if !ldr.AttrReachable(s) {
				continue
			}
			if uint64(ldr.SymValue(s)) >= sect.Vaddr {
				syms = syms[i:]
				break
			}
		}
		eaddr := int32(sect.Vaddr + sect.Length)
		for _, s := range syms {
			if !ldr.AttrReachable(s) {
				continue
			}
			if ldr.SymValue(s) >= int64(eaddr) {
				break
			}
			// Compute external relocations on the go, and pass to PEreloc1
			// to stream out.
			relocs := ldr.Relocs(s)
			for ri := 0; ri < relocs.Count(); ri++ {
				r := relocs.At(ri)
				rr, ok := extreloc(ctxt, ldr, s, r)
				if !ok {
					continue
				}
				if rr.Xsym == 0 {
					ctxt.Errorf(s, "missing xsym in relocation")
					continue
				}
				if ldr.SymDynid(rr.Xsym) < 0 {
					ctxt.Errorf(s, "reloc %d to non-coff symbol %s (outer=%s) %d", r.Type(), ldr.SymName(r.Sym()), ldr.SymName(rr.Xsym), ldr.SymType(r.Sym()))
				}
				if !thearch.PEreloc1(ctxt.Arch, ctxt.Out, ldr, s, rr, int64(uint64(ldr.SymValue(s)+int64(r.Off()))-base)) {
					ctxt.Errorf(s, "unsupported obj reloc %d/%d to %s", r.Type(), r.Siz(), ldr.SymName(r.Sym()))
				}
				nrelocs++
			}
		}
		sect.Rellen = uint64(ctxt.Out.Offset()) - sect.Reloff
		return nrelocs
	}

	sects := []struct {
		peSect *peSection
		seg    *sym.Segment
		syms   []loader.Sym
	}{
		{f.textSect, &Segtext, ctxt.Textp},
		{f.rdataSect, &Segrodata, ctxt.datap},
		{f.dataSect, &Segdata, ctxt.datap},
	}
	for _, s := range sects {
		s.peSect.emitRelocations(ctxt.Out, func() int {
			var n int
			for _, sect := range s.seg.Sections {
				n += relocsect(sect, s.syms, s.seg.Vaddr)
			}
			return n
		})
	}

dwarfLoop:
	for i := 0; i < len(Segdwarf.Sections); i++ {
		sect := Segdwarf.Sections[i]
		si := dwarfp[i]
		if si.secSym() != loader.Sym(sect.Sym) ||
			ldr.SymSect(si.secSym()) != sect {
			panic("inconsistency between dwarfp and Segdwarf")
		}
		for _, pesect := range f.sections {
			if sect.Name == pesect.name {
				pesect.emitRelocations(ctxt.Out, func() int {
					return relocsect(sect, si.syms, sect.Vaddr)
				})
				continue dwarfLoop
			}
		}
		Errorf(nil, "emitRelocations: could not find %q section", sect.Name)
	}

	f.ctorsSect.emitRelocations(ctxt.Out, func() int {
		dottext := ldr.Lookup(".text", 0)
		ctxt.Out.Write32(0)
		ctxt.Out.Write32(uint32(ldr.SymDynid(dottext)))
		switch objabi.GOARCH {
		default:
			ctxt.Errorf(dottext, "unknown architecture for PE: %q\n", objabi.GOARCH)
		case "386":
			ctxt.Out.Write16(IMAGE_REL_I386_DIR32)
		case "amd64":
			ctxt.Out.Write16(IMAGE_REL_AMD64_ADDR64)
		case "arm":
			ctxt.Out.Write16(IMAGE_REL_ARM_ADDR32)
		case "arm64":
			ctxt.Out.Write16(IMAGE_REL_ARM64_ADDR64)
		}
		return 1
	})
}

// writeSymbol appends symbol s to file f symbol table.
// It also sets s.Dynid to written symbol number.
func (f *peFile) writeSymbol(out *OutBuf, ldr *loader.Loader, s loader.Sym, name string, value int64, sectidx int, typ uint16, class uint8) {
	if len(name) > 8 {
		out.Write32(0)
		out.Write32(uint32(f.stringTable.add(name)))
	} else {
		out.WriteStringN(name, 8)
	}
	out.Write32(uint32(value))
	out.Write16(uint16(sectidx))
	out.Write16(typ)
	out.Write8(class)
	out.Write8(0) // no aux entries

	ldr.SetSymDynid(s, int32(f.symbolCount))

	f.symbolCount++
}

// mapToPESection searches peFile f for s symbol's location.
// It returns PE section index, and offset within that section.
func (f *peFile) mapToPESection(ldr *loader.Loader, s loader.Sym, linkmode LinkMode) (pesectidx int, offset int64, err error) {
	sect := ldr.SymSect(s)
	if sect == nil {
		return 0, 0, fmt.Errorf("could not map %s symbol with no section", ldr.SymName(s))
	}
	if sect.Seg == &Segtext {
		return f.textSect.index, int64(uint64(ldr.SymValue(s)) - Segtext.Vaddr), nil
	}
	if sect.Seg == &Segrodata {
		return f.rdataSect.index, int64(uint64(ldr.SymValue(s)) - Segrodata.Vaddr), nil
	}
	if sect.Seg != &Segdata {
		return 0, 0, fmt.Errorf("could not map %s symbol with non .text or .rdata or .data section", ldr.SymName(s))
	}
	v := uint64(ldr.SymValue(s)) - Segdata.Vaddr
	if linkmode != LinkExternal {
		return f.dataSect.index, int64(v), nil
	}
	if ldr.SymType(s) == sym.SDATA {
		return f.dataSect.index, int64(v), nil
	}
	// Note: although address of runtime.edata (type sym.SDATA) is at the start of .bss section
	// it still belongs to the .data section, not the .bss section.
	if v < Segdata.Filelen {
		return f.dataSect.index, int64(v), nil
	}
	return f.bssSect.index, int64(v - Segdata.Filelen), nil
}

// writeSymbols writes all COFF symbol table records.
func (f *peFile) writeSymbols(ctxt *Link) {
	ldr := ctxt.loader
	addsym := func(s loader.Sym) {
		t := ldr.SymType(s)
		if ldr.SymSect(s) == nil && t != sym.SDYNIMPORT && t != sym.SHOSTOBJ && t != sym.SUNDEFEXT {
			return
		}

		name := ldr.SymName(s)

		// Only windows/386 requires underscore prefix on external symbols.
		if ctxt.Is386() && ctxt.IsExternal() &&
			(t == sym.SHOSTOBJ || t == sym.SUNDEFEXT || ldr.AttrCgoExport(s)) {
			name = "_" + name
		}

		var peSymType uint16
		if ctxt.IsExternal() {
			peSymType = IMAGE_SYM_TYPE_NULL
		} else {
			// TODO: fix IMAGE_SYM_DTYPE_ARRAY value and use following expression, instead of 0x0308
			// peSymType = IMAGE_SYM_DTYPE_ARRAY<<8 + IMAGE_SYM_TYPE_STRUCT
			peSymType = 0x0308 // "array of structs"
		}
		sect, value, err := f.mapToPESection(ldr, s, ctxt.LinkMode)
		if err != nil {
			if t == sym.SDYNIMPORT || t == sym.SHOSTOBJ || t == sym.SUNDEFEXT {
				peSymType = IMAGE_SYM_DTYPE_FUNCTION
			} else {
				ctxt.Errorf(s, "addpesym: %v", err)
			}
		}
		class := IMAGE_SYM_CLASS_EXTERNAL
		if ldr.IsFileLocal(s) || ldr.AttrVisibilityHidden(s) || ldr.AttrLocal(s) {
			class = IMAGE_SYM_CLASS_STATIC
		}
		f.writeSymbol(ctxt.Out, ldr, s, name, value, sect, peSymType, uint8(class))
	}

	if ctxt.LinkMode == LinkExternal {
		// Include section symbols as external, because
		// .ctors and .debug_* section relocations refer to it.
		for _, pesect := range f.sections {
			s := ldr.LookupOrCreateSym(pesect.name, 0)
			f.writeSymbol(ctxt.Out, ldr, s, pesect.name, 0, pesect.index, IMAGE_SYM_TYPE_NULL, IMAGE_SYM_CLASS_STATIC)
		}
	}

	// Add special runtime.text and runtime.etext symbols.
	s := ldr.Lookup("runtime.text", 0)
	if ldr.SymType(s) == sym.STEXT {
		addsym(s)
	}
	s = ldr.Lookup("runtime.etext", 0)
	if ldr.SymType(s) == sym.STEXT {
		addsym(s)
	}

	// Add text symbols.
	for _, s := range ctxt.Textp {
		addsym(s)
	}

	shouldBeInSymbolTable := func(s loader.Sym) bool {
		if ldr.AttrNotInSymbolTable(s) {
			return false
		}
		name := ldr.RawSymName(s) // TODO: try not to read the name
		if name == "" || name[0] == '.' {
			return false
		}
		return true
	}

	// Add data symbols and external references.
	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
		if !ldr.AttrReachable(s) {
			continue
		}
		t := ldr.SymType(s)
		if t >= sym.SELFRXSECT && t < sym.SXREF { // data sections handled in dodata
			if t == sym.STLSBSS {
				continue
			}
			if !shouldBeInSymbolTable(s) {
				continue
			}
			addsym(s)
		}

		switch t {
		case sym.SDYNIMPORT, sym.SHOSTOBJ, sym.SUNDEFEXT:
			addsym(s)
		}
	}
}

// writeSymbolTableAndStringTable writes out symbol and string tables for peFile f.
func (f *peFile) writeSymbolTableAndStringTable(ctxt *Link) {
	f.symtabOffset = ctxt.Out.Offset()

	// write COFF symbol table
	if !*FlagS || ctxt.LinkMode == LinkExternal {
		f.writeSymbols(ctxt)
	}

	// update COFF file header and section table
	size := f.stringTable.size() + 18*f.symbolCount
	var h *peSection
	if ctxt.LinkMode != LinkExternal {
		// We do not really need .symtab for go.o, and if we have one, ld
		// will also include it in the exe, and that will confuse windows.
		h = f.addSection(".symtab", size, size)
		h.characteristics = IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_DISCARDABLE
		h.checkOffset(f.symtabOffset)
	}

	// write COFF string table
	f.stringTable.write(ctxt.Out)
	if ctxt.LinkMode != LinkExternal {
		h.pad(ctxt.Out, uint32(size))
	}
}

// writeFileHeader writes COFF file header for peFile f.
func (f *peFile) writeFileHeader(ctxt *Link) {
	var fh pe.FileHeader

	switch ctxt.Arch.Family {
	default:
		Exitf("unknown PE architecture: %v", ctxt.Arch.Family)
	case sys.AMD64:
		fh.Machine = pe.IMAGE_FILE_MACHINE_AMD64
	case sys.I386:
		fh.Machine = pe.IMAGE_FILE_MACHINE_I386
	case sys.ARM:
		fh.Machine = pe.IMAGE_FILE_MACHINE_ARMNT
	case sys.ARM64:
		fh.Machine = pe.IMAGE_FILE_MACHINE_ARM64
	}

	fh.NumberOfSections = uint16(len(f.sections))

	// Being able to produce identical output for identical input is
	// much more beneficial than having build timestamp in the header.
	fh.TimeDateStamp = 0

	if ctxt.LinkMode == LinkExternal {
		fh.Characteristics = pe.IMAGE_FILE_LINE_NUMS_STRIPPED
	} else {
		fh.Characteristics = pe.IMAGE_FILE_EXECUTABLE_IMAGE | pe.IMAGE_FILE_DEBUG_STRIPPED
		switch ctxt.Arch.Family {
		case sys.AMD64, sys.I386:
			if ctxt.BuildMode != BuildModePIE {
				fh.Characteristics |= pe.IMAGE_FILE_RELOCS_STRIPPED
			}
		}
	}
	if pe64 != 0 {
		var oh64 pe.OptionalHeader64
		fh.SizeOfOptionalHeader = uint16(binary.Size(&oh64))
		fh.Characteristics |= pe.IMAGE_FILE_LARGE_ADDRESS_AWARE
	} else {
		var oh pe.OptionalHeader32
		fh.SizeOfOptionalHeader = uint16(binary.Size(&oh))
		fh.Characteristics |= pe.IMAGE_FILE_32BIT_MACHINE
	}

	fh.PointerToSymbolTable = uint32(f.symtabOffset)
	fh.NumberOfSymbols = uint32(f.symbolCount)

	binary.Write(ctxt.Out, binary.LittleEndian, &fh)
}

// writeOptionalHeader writes COFF optional header for peFile f.
func (f *peFile) writeOptionalHeader(ctxt *Link) {
	var oh pe.OptionalHeader32
	var oh64 pe.OptionalHeader64

	if pe64 != 0 {
		oh64.Magic = 0x20b // PE32+
	} else {
		oh.Magic = 0x10b // PE32
		oh.BaseOfData = f.dataSect.virtualAddress
	}

	// Fill out both oh64 and oh. We only use one. Oh well.
	oh64.MajorLinkerVersion = 3
	oh.MajorLinkerVersion = 3
	oh64.MinorLinkerVersion = 0
	oh.MinorLinkerVersion = 0
	oh64.SizeOfCode = f.textSect.sizeOfRawData
	oh.SizeOfCode = f.textSect.sizeOfRawData
	oh64.SizeOfInitializedData = f.dataSect.sizeOfRawData
	oh.SizeOfInitializedData = f.dataSect.sizeOfRawData
	oh64.SizeOfUninitializedData = 0
	oh.SizeOfUninitializedData = 0
	if ctxt.LinkMode != LinkExternal {
		oh64.AddressOfEntryPoint = uint32(Entryvalue(ctxt) - PEBASE)
		oh.AddressOfEntryPoint = uint32(Entryvalue(ctxt) - PEBASE)
	}
	oh64.BaseOfCode = f.textSect.virtualAddress
	oh.BaseOfCode = f.textSect.virtualAddress
	oh64.ImageBase = uint64(PEBASE)
	oh.ImageBase = uint32(PEBASE)
	oh64.SectionAlignment = uint32(PESECTALIGN)
	oh.SectionAlignment = uint32(PESECTALIGN)
	oh64.FileAlignment = uint32(PEFILEALIGN)
	oh.FileAlignment = uint32(PEFILEALIGN)
	oh64.MajorOperatingSystemVersion = PeMinimumTargetMajorVersion
	oh.MajorOperatingSystemVersion = PeMinimumTargetMajorVersion
	oh64.MinorOperatingSystemVersion = PeMinimumTargetMinorVersion
	oh.MinorOperatingSystemVersion = PeMinimumTargetMinorVersion
	oh64.MajorImageVersion = 1
	oh.MajorImageVersion = 1
	oh64.MinorImageVersion = 0
	oh.MinorImageVersion = 0
	oh64.MajorSubsystemVersion = PeMinimumTargetMajorVersion
	oh.MajorSubsystemVersion = PeMinimumTargetMajorVersion
	oh64.MinorSubsystemVersion = PeMinimumTargetMinorVersion
	oh.MinorSubsystemVersion = PeMinimumTargetMinorVersion
	oh64.SizeOfImage = f.nextSectOffset
	oh.SizeOfImage = f.nextSectOffset
	oh64.SizeOfHeaders = uint32(PEFILEHEADR)
	oh.SizeOfHeaders = uint32(PEFILEHEADR)
	if windowsgui {
		oh64.Subsystem = pe.IMAGE_SUBSYSTEM_WINDOWS_GUI
		oh.Subsystem = pe.IMAGE_SUBSYSTEM_WINDOWS_GUI
	} else {
		oh64.Subsystem = pe.IMAGE_SUBSYSTEM_WINDOWS_CUI
		oh.Subsystem = pe.IMAGE_SUBSYSTEM_WINDOWS_CUI
	}

	// Mark as having awareness of terminal services, to avoid ancient compatibility hacks.
	oh64.DllCharacteristics |= pe.IMAGE_DLLCHARACTERISTICS_TERMINAL_SERVER_AWARE
	oh.DllCharacteristics |= pe.IMAGE_DLLCHARACTERISTICS_TERMINAL_SERVER_AWARE

	// Enable DEP
	oh64.DllCharacteristics |= pe.IMAGE_DLLCHARACTERISTICS_NX_COMPAT
	oh.DllCharacteristics |= pe.IMAGE_DLLCHARACTERISTICS_NX_COMPAT

	// The DLL can be relocated at load time.
	if needPEBaseReloc(ctxt) {
		oh64.DllCharacteristics |= pe.IMAGE_DLLCHARACTERISTICS_DYNAMIC_BASE
		oh.DllCharacteristics |= pe.IMAGE_DLLCHARACTERISTICS_DYNAMIC_BASE
	}

	// Image can handle a high entropy 64-bit virtual address space.
	if ctxt.BuildMode == BuildModePIE {
		oh64.DllCharacteristics |= pe.IMAGE_DLLCHARACTERISTICS_HIGH_ENTROPY_VA
	}

	// Disable stack growth as we don't want Windows to
	// fiddle with the thread stack limits, which we set
	// ourselves to circumvent the stack checks in the
	// Windows exception dispatcher.
	// Commit size must be strictly less than reserve
	// size otherwise reserve will be rounded up to a
	// larger size, as verified with VMMap.

	// On 64-bit, we always reserve 2MB stacks. "Pure" Go code is
	// okay with much smaller stacks, but the syscall package
	// makes it easy to call into arbitrary C code without cgo,
	// and system calls even in "pure" Go code are actually C
	// calls that may need more stack than we think.
	//
	// The default stack reserve size directly affects only the main
	// thread, ctrlhandler thread, and profileloop thread. For
	// these, it must be greater than the stack size assumed by
	// externalthreadhandler.
	//
	// For other threads, the runtime explicitly asks the kernel
	// to use the default stack size so that all stacks are
	// consistent.
	//
	// At thread start, in minit, the runtime queries the OS for
	// the actual stack bounds so that the stack size doesn't need
	// to be hard-coded into the runtime.
	oh64.SizeOfStackReserve = 0x00200000
	if !iscgo {
		oh64.SizeOfStackCommit = 0x00001000
	} else {
		// TODO(brainman): Maybe remove optional header writing altogether for cgo.
		// For cgo it is the external linker that is building final executable.
		// And it probably does not use any information stored in optional header.
		oh64.SizeOfStackCommit = 0x00200000 - 0x2000 // account for 2 guard pages
	}

	oh.SizeOfStackReserve = 0x00100000
	if !iscgo {
		oh.SizeOfStackCommit = 0x00001000
	} else {
		oh.SizeOfStackCommit = 0x00100000 - 0x2000 // account for 2 guard pages
	}

	oh64.SizeOfHeapReserve = 0x00100000
	oh.SizeOfHeapReserve = 0x00100000
	oh64.SizeOfHeapCommit = 0x00001000
	oh.SizeOfHeapCommit = 0x00001000
	oh64.NumberOfRvaAndSizes = 16
	oh.NumberOfRvaAndSizes = 16

	if pe64 != 0 {
		oh64.DataDirectory = f.dataDirectory
	} else {
		oh.DataDirectory = f.dataDirectory
	}

	if pe64 != 0 {
		binary.Write(ctxt.Out, binary.LittleEndian, &oh64)
	} else {
		binary.Write(ctxt.Out, binary.LittleEndian, &oh)
	}
}

var pefile peFile

func Peinit(ctxt *Link) {
	var l int

	if ctxt.Arch.PtrSize == 8 {
		// 64-bit architectures
		pe64 = 1
		PEBASE = 1 << 32
		if ctxt.Arch.Family == sys.AMD64 {
			// TODO(rsc): For cgo we currently use 32-bit relocations
			// that fail when PEBASE is too large.
			// We need to fix this, but for now, use a smaller PEBASE.
			PEBASE = 1 << 22
		}
		var oh64 pe.OptionalHeader64
		l = binary.Size(&oh64)
	} else {
		// 32-bit architectures
		PEBASE = 1 << 22
		var oh pe.OptionalHeader32
		l = binary.Size(&oh)
	}

	if ctxt.LinkMode == LinkExternal {
		// .rdata section will contain "masks" and "shifts" symbols, and they
		// need to be aligned to 16-bytes. So make all sections aligned
		// to 32-byte and mark them all IMAGE_SCN_ALIGN_32BYTES so external
		// linker will honour that requirement.
		PESECTALIGN = 32
		PEFILEALIGN = 0
	}

	var sh [16]pe.SectionHeader32
	var fh pe.FileHeader
	PEFILEHEADR = int32(Rnd(int64(len(dosstub)+binary.Size(&fh)+l+binary.Size(&sh)), PEFILEALIGN))
	if ctxt.LinkMode != LinkExternal {
		PESECTHEADR = int32(Rnd(int64(PEFILEHEADR), PESECTALIGN))
	} else {
		PESECTHEADR = 0
	}
	pefile.nextSectOffset = uint32(PESECTHEADR)
	pefile.nextFileOffset = uint32(PEFILEHEADR)

	if ctxt.LinkMode == LinkInternal {
		// some mingw libs depend on this symbol, for example, FindPESectionByName
		for _, name := range [2]string{"__image_base__", "_image_base__"} {
			sb := ctxt.loader.CreateSymForUpdate(name, 0)
			sb.SetType(sym.SDATA)
			sb.SetValue(PEBASE)
			ctxt.loader.SetAttrSpecial(sb.Sym(), true)
			ctxt.loader.SetAttrLocal(sb.Sym(), true)
		}
	}

	HEADR = PEFILEHEADR
	if *FlagTextAddr == -1 {
		*FlagTextAddr = PEBASE + int64(PESECTHEADR)
	}
	if *FlagRound == -1 {
		*FlagRound = int(PESECTALIGN)
	}
}

func pewrite(ctxt *Link) {
	ctxt.Out.SeekSet(0)
	if ctxt.LinkMode != LinkExternal {
		ctxt.Out.Write(dosstub)
		ctxt.Out.WriteStringN("PE", 4)
	}

	pefile.writeFileHeader(ctxt)

	pefile.writeOptionalHeader(ctxt)

	for _, sect := range pefile.sections {
		sect.write(ctxt.Out, ctxt.LinkMode)
	}
}

func strput(out *OutBuf, s string) {
	out.WriteString(s)
	out.Write8(0)
	// string must be padded to even size
	if (len(s)+1)%2 != 0 {
		out.Write8(0)
	}
}

func initdynimport(ctxt *Link) *Dll {
	ldr := ctxt.loader
	var d *Dll

	dr = nil
	var m *Imp
	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
		if !ldr.AttrReachable(s) || ldr.SymType(s) != sym.SDYNIMPORT {
			continue
		}
		dynlib := ldr.SymDynimplib(s)
		for d = dr; d != nil; d = d.next {
			if d.name == dynlib {
				m = new(Imp)
				break
			}
		}

		if d == nil {
			d = new(Dll)
			d.name = dynlib
			d.next = dr
			dr = d
			m = new(Imp)
		}

		// Because external link requires properly stdcall decorated name,
		// all external symbols in runtime use %n to denote that the number
		// of uinptrs this function consumes. Store the argsize and discard
		// the %n suffix if any.
		m.argsize = -1
		extName := ldr.SymExtname(s)
		if i := strings.IndexByte(extName, '%'); i >= 0 {
			var err error
			m.argsize, err = strconv.Atoi(extName[i+1:])
			if err != nil {
				ctxt.Errorf(s, "failed to parse stdcall decoration: %v", err)
			}
			m.argsize *= ctxt.Arch.PtrSize
			ldr.SetSymExtname(s, extName[:i])
		}

		m.s = s
		m.next = d.ms
		d.ms = m
	}

	if ctxt.IsExternal() {
		// Add real symbol name
		for d := dr; d != nil; d = d.next {
			for m = d.ms; m != nil; m = m.next {
				sb := ldr.MakeSymbolUpdater(m.s)
				sb.SetType(sym.SDATA)
				sb.Grow(int64(ctxt.Arch.PtrSize))
				dynName := sb.Extname()
				// only windows/386 requires stdcall decoration
				if ctxt.Is386() && m.argsize >= 0 {
					dynName += fmt.Sprintf("@%d", m.argsize)
				}
				dynSym := ldr.CreateSymForUpdate(dynName, 0)
				dynSym.SetType(sym.SHOSTOBJ)
				r, _ := sb.AddRel(objabi.R_ADDR)
				r.SetSym(dynSym.Sym())
				r.SetSiz(uint8(ctxt.Arch.PtrSize))
			}
		}
	} else {
		dynamic := ldr.CreateSymForUpdate(".windynamic", 0)
		dynamic.SetType(sym.SWINDOWS)
		for d := dr; d != nil; d = d.next {
			for m = d.ms; m != nil; m = m.next {
				sb := ldr.MakeSymbolUpdater(m.s)
				sb.SetType(sym.SWINDOWS)
				sb.SetValue(dynamic.Size())
				dynamic.SetSize(dynamic.Size() + int64(ctxt.Arch.PtrSize))
				dynamic.AddInteriorSym(m.s)
			}

			dynamic.SetSize(dynamic.Size() + int64(ctxt.Arch.PtrSize))
		}
	}

	return dr
}

// peimporteddlls returns the gcc command line argument to link all imported
// DLLs.
func peimporteddlls() []string {
	var dlls []string

	for d := dr; d != nil; d = d.next {
		dlls = append(dlls, "-l"+strings.TrimSuffix(d.name, ".dll"))
	}

	return dlls
}

func addimports(ctxt *Link, datsect *peSection) {
	ldr := ctxt.loader
	startoff := ctxt.Out.Offset()
	dynamic := ldr.LookupOrCreateSym(".windynamic", 0)

	// skip import descriptor table (will write it later)
	n := uint64(0)

	for d := dr; d != nil; d = d.next {
		n++
	}
	ctxt.Out.SeekSet(startoff + int64(binary.Size(&IMAGE_IMPORT_DESCRIPTOR{}))*int64(n+1))

	// write dll names
	for d := dr; d != nil; d = d.next {
		d.nameoff = uint64(ctxt.Out.Offset()) - uint64(startoff)
		strput(ctxt.Out, d.name)
	}

	// write function names
	for d := dr; d != nil; d = d.next {
		for m := d.ms; m != nil; m = m.next {
			m.off = uint64(pefile.nextSectOffset) + uint64(ctxt.Out.Offset()) - uint64(startoff)
			ctxt.Out.Write16(0) // hint
			strput(ctxt.Out, ldr.SymExtname(m.s))
		}
	}

	// write OriginalFirstThunks
	oftbase := uint64(ctxt.Out.Offset()) - uint64(startoff)

	n = uint64(ctxt.Out.Offset())
	for d := dr; d != nil; d = d.next {
		d.thunkoff = uint64(ctxt.Out.Offset()) - n
		for m := d.ms; m != nil; m = m.next {
			if pe64 != 0 {
				ctxt.Out.Write64(m.off)
			} else {
				ctxt.Out.Write32(uint32(m.off))
			}
		}

		if pe64 != 0 {
			ctxt.Out.Write64(0)
		} else {
			ctxt.Out.Write32(0)
		}
	}

	// add pe section and pad it at the end
	n = uint64(ctxt.Out.Offset()) - uint64(startoff)

	isect := pefile.addSection(".idata", int(n), int(n))
	isect.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE
	isect.checkOffset(startoff)
	isect.pad(ctxt.Out, uint32(n))
	endoff := ctxt.Out.Offset()

	// write FirstThunks (allocated in .data section)
	ftbase := uint64(ldr.SymValue(dynamic)) - uint64(datsect.virtualAddress) - uint64(PEBASE)

	ctxt.Out.SeekSet(int64(uint64(datsect.pointerToRawData) + ftbase))
	for d := dr; d != nil; d = d.next {
		for m := d.ms; m != nil; m = m.next {
			if pe64 != 0 {
				ctxt.Out.Write64(m.off)
			} else {
				ctxt.Out.Write32(uint32(m.off))
			}
		}

		if pe64 != 0 {
			ctxt.Out.Write64(0)
		} else {
			ctxt.Out.Write32(0)
		}
	}

	// finally write import descriptor table
	out := ctxt.Out
	out.SeekSet(startoff)

	for d := dr; d != nil; d = d.next {
		out.Write32(uint32(uint64(isect.virtualAddress) + oftbase + d.thunkoff))
		out.Write32(0)
		out.Write32(0)
		out.Write32(uint32(uint64(isect.virtualAddress) + d.nameoff))
		out.Write32(uint32(uint64(datsect.virtualAddress) + ftbase + d.thunkoff))
	}

	out.Write32(0) //end
	out.Write32(0)
	out.Write32(0)
	out.Write32(0)
	out.Write32(0)

	// update data directory
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress = isect.virtualAddress
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_IMPORT].Size = isect.virtualSize
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_IAT].VirtualAddress = uint32(ldr.SymValue(dynamic) - PEBASE)
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_IAT].Size = uint32(ldr.SymSize(dynamic))

	out.SeekSet(endoff)
}

func initdynexport(ctxt *Link) {
	ldr := ctxt.loader
	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
		if !ldr.AttrReachable(s) || !ldr.AttrCgoExportDynamic(s) {
			continue
		}
		if len(dexport)+1 > cap(dexport) {
			ctxt.Errorf(s, "pe dynexport table is full")
			errorexit()
		}

		dexport = append(dexport, s)
	}

	sort.Slice(dexport, func(i, j int) bool { return ldr.SymExtname(dexport[i]) < ldr.SymExtname(dexport[j]) })
}

func addexports(ctxt *Link) {
	ldr := ctxt.loader
	var e IMAGE_EXPORT_DIRECTORY

	nexport := len(dexport)
	size := binary.Size(&e) + 10*nexport + len(*flagOutfile) + 1
	for _, s := range dexport {
		size += len(ldr.SymExtname(s)) + 1
	}

	if nexport == 0 {
		return
	}

	sect := pefile.addSection(".edata", size, size)
	sect.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
	sect.checkOffset(ctxt.Out.Offset())
	va := int(sect.virtualAddress)
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress = uint32(va)
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_EXPORT].Size = sect.virtualSize

	vaName := va + binary.Size(&e) + nexport*4
	vaAddr := va + binary.Size(&e)
	vaNa := va + binary.Size(&e) + nexport*8

	e.Characteristics = 0
	e.MajorVersion = 0
	e.MinorVersion = 0
	e.NumberOfFunctions = uint32(nexport)
	e.NumberOfNames = uint32(nexport)
	e.Name = uint32(va+binary.Size(&e)) + uint32(nexport)*10 // Program names.
	e.Base = 1
	e.AddressOfFunctions = uint32(vaAddr)
	e.AddressOfNames = uint32(vaName)
	e.AddressOfNameOrdinals = uint32(vaNa)

	out := ctxt.Out

	// put IMAGE_EXPORT_DIRECTORY
	binary.Write(out, binary.LittleEndian, &e)

	// put EXPORT Address Table
	for _, s := range dexport {
		out.Write32(uint32(ldr.SymValue(s) - PEBASE))
	}

	// put EXPORT Name Pointer Table
	v := int(e.Name + uint32(len(*flagOutfile)) + 1)

	for _, s := range dexport {
		out.Write32(uint32(v))
		v += len(ldr.SymExtname(s)) + 1
	}

	// put EXPORT Ordinal Table
	for i := 0; i < nexport; i++ {
		out.Write16(uint16(i))
	}

	// put Names
	out.WriteStringN(*flagOutfile, len(*flagOutfile)+1)

	for _, s := range dexport {
		name := ldr.SymExtname(s)
		out.WriteStringN(name, len(name)+1)
	}
	sect.pad(out, uint32(size))
}

// peBaseRelocEntry represents a single relocation entry.
type peBaseRelocEntry struct {
	typeOff uint16
}

// peBaseRelocBlock represents a Base Relocation Block. A block
// is a collection of relocation entries in a page, where each
// entry describes a single relocation.
// The block page RVA (Relative Virtual Address) is the index
// into peBaseRelocTable.blocks.
type peBaseRelocBlock struct {
	entries []peBaseRelocEntry
}

// pePages is a type used to store the list of pages for which there
// are base relocation blocks. This is defined as a type so that
// it can be sorted.
type pePages []uint32

func (p pePages) Len() int           { return len(p) }
func (p pePages) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
func (p pePages) Less(i, j int) bool { return p[i] < p[j] }

// A PE base relocation table is a list of blocks, where each block
// contains relocation information for a single page. The blocks
// must be emitted in order of page virtual address.
// See https://docs.microsoft.com/en-us/windows/desktop/debug/pe-format#the-reloc-section-image-only
type peBaseRelocTable struct {
	blocks map[uint32]peBaseRelocBlock

	// pePages is a list of keys into blocks map.
	// It is stored separately for ease of sorting.
	pages pePages
}

func (rt *peBaseRelocTable) init(ctxt *Link) {
	rt.blocks = make(map[uint32]peBaseRelocBlock)
}

func (rt *peBaseRelocTable) addentry(ldr *loader.Loader, s loader.Sym, r *loader.Reloc) {
	// pageSize is the size in bytes of a page
	// described by a base relocation block.
	const pageSize = 0x1000
	const pageMask = pageSize - 1

	addr := ldr.SymValue(s) + int64(r.Off()) - int64(PEBASE)
	page := uint32(addr &^ pageMask)
	off := uint32(addr & pageMask)

	b, ok := rt.blocks[page]
	if !ok {
		rt.pages = append(rt.pages, page)
	}

	e := peBaseRelocEntry{
		typeOff: uint16(off & 0xFFF),
	}

	// Set entry type
	switch r.Siz() {
	default:
		Exitf("unsupported relocation size %d\n", r.Siz)
	case 4:
		e.typeOff |= uint16(IMAGE_REL_BASED_HIGHLOW << 12)
	case 8:
		e.typeOff |= uint16(IMAGE_REL_BASED_DIR64 << 12)
	}

	b.entries = append(b.entries, e)
	rt.blocks[page] = b
}

func (rt *peBaseRelocTable) write(ctxt *Link) {
	out := ctxt.Out

	// sort the pages array
	sort.Sort(rt.pages)

	for _, p := range rt.pages {
		b := rt.blocks[p]
		const sizeOfPEbaseRelocBlock = 8 // 2 * sizeof(uint32)
		blockSize := uint32(sizeOfPEbaseRelocBlock + len(b.entries)*2)
		out.Write32(p)
		out.Write32(blockSize)

		for _, e := range b.entries {
			out.Write16(e.typeOff)
		}
	}
}

func addPEBaseRelocSym(ldr *loader.Loader, s loader.Sym, rt *peBaseRelocTable) {
	relocs := ldr.Relocs(s)
	for ri := 0; ri < relocs.Count(); ri++ {
		r := relocs.At(ri)
		if r.Type() >= objabi.ElfRelocOffset {
			continue
		}
		if r.Siz() == 0 { // informational relocation
			continue
		}
		if r.Type() == objabi.R_DWARFFILEREF {
			continue
		}
		rs := r.Sym()
		rs = ldr.ResolveABIAlias(rs)
		if rs == 0 {
			continue
		}
		if !ldr.AttrReachable(s) {
			continue
		}

		switch r.Type() {
		default:
		case objabi.R_ADDR:
			rt.addentry(ldr, s, &r)
		}
	}
}

func needPEBaseReloc(ctxt *Link) bool {
	// Non-PIE x86 binaries don't need the base relocation table.
	// Everyone else does.
	if (ctxt.Arch.Family == sys.I386 || ctxt.Arch.Family == sys.AMD64) && ctxt.BuildMode != BuildModePIE {
		return false
	}
	return true
}

func addPEBaseReloc(ctxt *Link) {
	if !needPEBaseReloc(ctxt) {
		return
	}

	var rt peBaseRelocTable
	rt.init(ctxt)

	// Get relocation information
	ldr := ctxt.loader
	for _, s := range ctxt.Textp {
		addPEBaseRelocSym(ldr, s, &rt)
	}
	for _, s := range ctxt.datap {
		addPEBaseRelocSym(ldr, s, &rt)
	}

	// Write relocation information
	startoff := ctxt.Out.Offset()
	rt.write(ctxt)
	size := ctxt.Out.Offset() - startoff

	// Add a PE section and pad it at the end
	rsect := pefile.addSection(".reloc", int(size), int(size))
	rsect.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_DISCARDABLE
	rsect.checkOffset(startoff)
	rsect.pad(ctxt.Out, uint32(size))

	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_BASERELOC].VirtualAddress = rsect.virtualAddress
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_BASERELOC].Size = rsect.virtualSize
}

func (ctxt *Link) dope() {
	initdynimport(ctxt)
	initdynexport(ctxt)
}

func setpersrc(ctxt *Link, syms []loader.Sym) {
	if len(rsrcsyms) != 0 {
		Errorf(nil, "too many .rsrc sections")
	}
	rsrcsyms = syms
}

func addpersrc(ctxt *Link) {
	if len(rsrcsyms) == 0 {
		return
	}

	var size int64
	for _, rsrcsym := range rsrcsyms {
		size += ctxt.loader.SymSize(rsrcsym)
	}
	h := pefile.addSection(".rsrc", int(size), int(size))
	h.characteristics = IMAGE_SCN_MEM_READ | IMAGE_SCN_CNT_INITIALIZED_DATA
	h.checkOffset(ctxt.Out.Offset())

	for _, rsrcsym := range rsrcsyms {
		// A split resource happens when the actual resource data and its relocations are
		// split across multiple sections, denoted by a $01 or $02 at the end of the .rsrc
		// section name.
		splitResources := strings.Contains(ctxt.loader.SymName(rsrcsym), ".rsrc$")
		relocs := ctxt.loader.Relocs(rsrcsym)
		data := ctxt.loader.Data(rsrcsym)
		for ri := 0; ri < relocs.Count(); ri++ {
			r := relocs.At(ri)
			p := data[r.Off():]
			val := uint32(int64(h.virtualAddress) + r.Add())
			if splitResources {
				// If we're a split resource section, and that section has relocation
				// symbols, then the data that it points to doesn't actually begin at
				// the virtual address listed in this current section, but rather
				// begins at the section immediately after this one. So, in order to
				// calculate the proper virtual address of the data it's pointing to,
				// we have to add the length of this section to the virtual address.
				// This works because .rsrc sections are divided into two (but not more)
				// of these sections.
				val += uint32(len(data))
			}
			binary.LittleEndian.PutUint32(p, val)
		}
		ctxt.Out.Write(data)
	}
	h.pad(ctxt.Out, uint32(size))

	// update data directory
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_RESOURCE].VirtualAddress = h.virtualAddress
	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_RESOURCE].Size = h.virtualSize
}

func asmbPe(ctxt *Link) {
	t := pefile.addSection(".text", int(Segtext.Length), int(Segtext.Length))
	t.characteristics = IMAGE_SCN_CNT_CODE | IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_READ
	if ctxt.LinkMode == LinkExternal {
		// some data symbols (e.g. masks) end up in the .text section, and they normally
		// expect larger alignment requirement than the default text section alignment.
		t.characteristics |= IMAGE_SCN_ALIGN_32BYTES
	}
	t.checkSegment(&Segtext)
	pefile.textSect = t

	ro := pefile.addSection(".rdata", int(Segrodata.Length), int(Segrodata.Length))
	ro.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
	if ctxt.LinkMode == LinkExternal {
		// some data symbols (e.g. masks) end up in the .rdata section, and they normally
		// expect larger alignment requirement than the default text section alignment.
		ro.characteristics |= IMAGE_SCN_ALIGN_32BYTES
	}
	ro.checkSegment(&Segrodata)
	pefile.rdataSect = ro

	var d *peSection
	if ctxt.LinkMode != LinkExternal {
		d = pefile.addSection(".data", int(Segdata.Length), int(Segdata.Filelen))
		d.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE
		d.checkSegment(&Segdata)
		pefile.dataSect = d
	} else {
		d = pefile.addSection(".data", int(Segdata.Filelen), int(Segdata.Filelen))
		d.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_ALIGN_32BYTES
		d.checkSegment(&Segdata)
		pefile.dataSect = d

		b := pefile.addSection(".bss", int(Segdata.Length-Segdata.Filelen), 0)
		b.characteristics = IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_ALIGN_32BYTES
		b.pointerToRawData = 0
		pefile.bssSect = b
	}

	pefile.addDWARF()

	if ctxt.LinkMode == LinkExternal {
		pefile.ctorsSect = pefile.addInitArray(ctxt)
	}

	ctxt.Out.SeekSet(int64(pefile.nextFileOffset))
	if ctxt.LinkMode != LinkExternal {
		addimports(ctxt, d)
		addexports(ctxt)
		addPEBaseReloc(ctxt)
	}
	pefile.writeSymbolTableAndStringTable(ctxt)
	addpersrc(ctxt)
	if ctxt.LinkMode == LinkExternal {
		pefile.emitRelocations(ctxt)
	}

	pewrite(ctxt)
}