github.com/megatontech/mynoteforgo@v0.0.0-20200507084910-5d0c6ea6e890/源码/cmd/link/internal/ld/xcoff.go

// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package ld

import (
	"bytes"
	"cmd/internal/objabi"
	"cmd/link/internal/sym"
	"encoding/binary"
	"strings"
)

// This file handles all algorithms related to XCOFF files generation.
// Most of them are adaptations of the ones in  cmd/link/internal/pe.go
// as PE and XCOFF are based on COFF files.
// XCOFF files generated are 64 bits.

const (
	// Total amount of space to reserve at the start of the file
	// for File Header, Auxiliary Header, and Section Headers.
	// May waste some.
	XCOFFHDRRESERVE       = FILHSZ_64 + AOUTHSZ_EXEC64 + SCNHSZ_64*23
	XCOFFSECTALIGN  int64 = 32 // base on dump -o

	// XCOFF binaries should normally have all its sections position-independent.
	// However, this is not yet possible for .text because of some R_ADDR relocations
	// inside RODATA symbols.
	// .data and .bss are position-independent so their address start inside a unreachable
	// segment during execution to force segfault if something is wrong.
	XCOFFTEXTBASE = 0x100000000 // Start of text address
	XCOFFDATABASE = 0x200000000 // Start of data address
)

// File Header
type XcoffFileHdr64 struct {
	Fmagic   uint16 // Target machine
	Fnscns   uint16 // Number of sections
	Ftimedat int32  // Time and date of file creation
	Fsymptr  uint64 // Byte offset to symbol table start
	Fopthdr  uint16 // Number of bytes in optional header
	Fflags   uint16 // Flags
	Fnsyms   int32  // Number of entries in symbol table
}

const (
	U64_TOCMAGIC = 0767 // AIX 64-bit XCOFF
)

// Flags that describe the type of the object file.
const (
	F_RELFLG    = 0x0001
	F_EXEC      = 0x0002
	F_LNNO      = 0x0004
	F_FDPR_PROF = 0x0010
	F_FDPR_OPTI = 0x0020
	F_DSA       = 0x0040
	F_VARPG     = 0x0100
	F_DYNLOAD   = 0x1000
	F_SHROBJ    = 0x2000
	F_LOADONLY  = 0x4000
)

// Auxiliary Header
type XcoffAoutHdr64 struct {
	Omagic      int16    // Flags - Ignored If Vstamp Is 1
	Ovstamp     int16    // Version
	Odebugger   uint32   // Reserved For Debugger
	Otextstart  uint64   // Virtual Address Of Text
	Odatastart  uint64   // Virtual Address Of Data
	Otoc        uint64   // Toc Address
	Osnentry    int16    // Section Number For Entry Point
	Osntext     int16    // Section Number For Text
	Osndata     int16    // Section Number For Data
	Osntoc      int16    // Section Number For Toc
	Osnloader   int16    // Section Number For Loader
	Osnbss      int16    // Section Number For Bss
	Oalgntext   int16    // Max Text Alignment
	Oalgndata   int16    // Max Data Alignment
	Omodtype    [2]byte  // Module Type Field
	Ocpuflag    uint8    // Bit Flags - Cputypes Of Objects
	Ocputype    uint8    // Reserved for CPU type
	Otextpsize  uint8    // Requested text page size
	Odatapsize  uint8    // Requested data page size
	Ostackpsize uint8    // Requested stack page size
	Oflags      uint8    // Flags And TLS Alignment
	Otsize      uint64   // Text Size In Bytes
	Odsize      uint64   // Data Size In Bytes
	Obsize      uint64   // Bss Size In Bytes
	Oentry      uint64   // Entry Point Address
	Omaxstack   uint64   // Max Stack Size Allowed
	Omaxdata    uint64   // Max Data Size Allowed
	Osntdata    int16    // Section Number For Tdata Section
	Osntbss     int16    // Section Number For Tbss Section
	Ox64flags   uint16   // Additional Flags For 64-Bit Objects
	Oresv3a     int16    // Reserved
	Oresv3      [2]int32 // Reserved

}

// Section Header
type XcoffScnHdr64 struct {
	Sname    [8]byte // Section Name
	Spaddr   uint64  // Physical Address
	Svaddr   uint64  // Virtual Address
	Ssize    uint64  // Section Size
	Sscnptr  uint64  // File Offset To Raw Data
	Srelptr  uint64  // File Offset To Relocation
	Slnnoptr uint64  // File Offset To Line Numbers
	Snreloc  uint32  // Number Of Relocation Entries
	Snlnno   uint32  // Number Of Line Number Entries
	Sflags   uint32  // flags
}

// Flags defining the section type.
const (
	STYP_DWARF  = 0x0010
	STYP_TEXT   = 0x0020
	STYP_DATA   = 0x0040
	STYP_BSS    = 0x0080
	STYP_EXCEPT = 0x0100
	STYP_INFO   = 0x0200
	STYP_TDATA  = 0x0400
	STYP_TBSS   = 0x0800
	STYP_LOADER = 0x1000
	STYP_DEBUG  = 0x2000
	STYP_TYPCHK = 0x4000
	STYP_OVRFLO = 0x8000
)
const (
	SSUBTYP_DWINFO  = 0x10000 // DWARF info section
	SSUBTYP_DWLINE  = 0x20000 // DWARF line-number section
	SSUBTYP_DWPBNMS = 0x30000 // DWARF public names section
	SSUBTYP_DWPBTYP = 0x40000 // DWARF public types section
	SSUBTYP_DWARNGE = 0x50000 // DWARF aranges section
	SSUBTYP_DWABREV = 0x60000 // DWARF abbreviation section
	SSUBTYP_DWSTR   = 0x70000 // DWARF strings section
	SSUBTYP_DWRNGES = 0x80000 // DWARF ranges section
	SSUBTYP_DWLOC   = 0x90000 // DWARF location lists section
	SSUBTYP_DWFRAME = 0xA0000 // DWARF frames section
	SSUBTYP_DWMAC   = 0xB0000 // DWARF macros section
)

// Headers size
const (
	FILHSZ_32      = 20
	FILHSZ_64      = 24
	AOUTHSZ_EXEC32 = 72
	AOUTHSZ_EXEC64 = 120
	SCNHSZ_32      = 40
	SCNHSZ_64      = 72
	LDHDRSZ_32     = 32
	LDHDRSZ_64     = 56
	LDSYMSZ_64     = 24
)

// Symbol Table Entry
type XcoffSymEnt64 struct {
	Nvalue  uint64 // Symbol value
	Noffset uint32 // Offset of the name in string table or .debug section
	Nscnum  int16  // Section number of symbol
	Ntype   uint16 // Basic and derived type specification
	Nsclass uint8  // Storage class of symbol
	Nnumaux int8   // Number of auxiliary entries
}

const SYMESZ = 18

const (
	// Nscnum
	N_DEBUG = -2
	N_ABS   = -1
	N_UNDEF = 0

	//Ntype
	SYM_V_INTERNAL  = 0x1000
	SYM_V_HIDDEN    = 0x2000
	SYM_V_PROTECTED = 0x3000
	SYM_V_EXPORTED  = 0x4000
	SYM_TYPE_FUNC   = 0x0020 // is function
)

// Storage Class.
const (
	C_NULL    = 0   // Symbol table entry marked for deletion
	C_EXT     = 2   // External symbol
	C_STAT    = 3   // Static symbol
	C_BLOCK   = 100 // Beginning or end of inner block
	C_FCN     = 101 // Beginning or end of function
	C_FILE    = 103 // Source file name and compiler information
	C_HIDEXT  = 107 // Unnamed external symbol
	C_BINCL   = 108 // Beginning of include file
	C_EINCL   = 109 // End of include file
	C_WEAKEXT = 111 // Weak external symbol
	C_DWARF   = 112 // DWARF symbol
	C_GSYM    = 128 // Global variable
	C_LSYM    = 129 // Automatic variable allocated on stack
	C_PSYM    = 130 // Argument to subroutine allocated on stack
	C_RSYM    = 131 // Register variable
	C_RPSYM   = 132 // Argument to function or procedure stored in register
	C_STSYM   = 133 // Statically allocated symbol
	C_BCOMM   = 135 // Beginning of common block
	C_ECOML   = 136 // Local member of common block
	C_ECOMM   = 137 // End of common block
	C_DECL    = 140 // Declaration of object
	C_ENTRY   = 141 // Alternate entry
	C_FUN     = 142 // Function or procedure
	C_BSTAT   = 143 // Beginning of static block
	C_ESTAT   = 144 // End of static block
	C_GTLS    = 145 // Global thread-local variable
	C_STTLS   = 146 // Static thread-local variable
)

// File Auxiliary Entry
type XcoffAuxFile64 struct {
	Xfname   [8]byte // Name or offset inside string table
	Xftype   uint8   // Source file string type
	Xauxtype uint8   // Type of auxiliary entry
}

// Function Auxiliary Entry
type XcoffAuxFcn64 struct {
	Xlnnoptr uint64 // File pointer to line number
	Xfsize   uint32 // Size of function in bytes
	Xendndx  uint32 // Symbol table index of next entry
	Xpad     uint8  // Unused
	Xauxtype uint8  // Type of auxiliary entry
}

// csect Auxiliary Entry.
type XcoffAuxCSect64 struct {
	Xscnlenlo uint32 // Lower 4 bytes of length or symbol table index
	Xparmhash uint32 // Offset of parameter type-check string
	Xsnhash   uint16 // .typchk section number
	Xsmtyp    uint8  // Symbol alignment and type
	Xsmclas   uint8  // Storage-mapping class
	Xscnlenhi uint32 // Upper 4 bytes of length or symbol table index
	Xpad      uint8  // Unused
	Xauxtype  uint8  // Type of auxiliary entry
}

// Auxiliary type
const (
	_AUX_EXCEPT = 255
	_AUX_FCN    = 254
	_AUX_SYM    = 253
	_AUX_FILE   = 252
	_AUX_CSECT  = 251
	_AUX_SECT   = 250
)

// Xftype field
const (
	XFT_FN = 0   // Source File Name
	XFT_CT = 1   // Compile Time Stamp
	XFT_CV = 2   // Compiler Version Number
	XFT_CD = 128 // Compiler Defined Information/

)

// Symbol type field.
const (
	XTY_ER  = 0    // External reference
	XTY_SD  = 1    // Section definition
	XTY_LD  = 2    // Label definition
	XTY_CM  = 3    // Common csect definition
	XTY_WK  = 0x8  // Weak symbol
	XTY_EXP = 0x10 // Exported symbol
	XTY_ENT = 0x20 // Entry point symbol
	XTY_IMP = 0x40 // Imported symbol
)

// Storage-mapping class.
const (
	XMC_PR     = 0  // Program code
	XMC_RO     = 1  // Read-only constant
	XMC_DB     = 2  // Debug dictionary table
	XMC_TC     = 3  // TOC entry
	XMC_UA     = 4  // Unclassified
	XMC_RW     = 5  // Read/Write data
	XMC_GL     = 6  // Global linkage
	XMC_XO     = 7  // Extended operation
	XMC_SV     = 8  // 32-bit supervisor call descriptor
	XMC_BS     = 9  // BSS class
	XMC_DS     = 10 // Function descriptor
	XMC_UC     = 11 // Unnamed FORTRAN common
	XMC_TC0    = 15 // TOC anchor
	XMC_TD     = 16 // Scalar data entry in the TOC
	XMC_SV64   = 17 // 64-bit supervisor call descriptor
	XMC_SV3264 = 18 // Supervisor call descriptor for both 32-bit and 64-bit
	XMC_TL     = 20 // Read/Write thread-local data
	XMC_UL     = 21 // Read/Write thread-local data (.tbss)
	XMC_TE     = 22 // TOC entry
)

// Loader Header
type XcoffLdHdr64 struct {
	Lversion int32  // Loader section version number
	Lnsyms   int32  // Number of symbol table entries
	Lnreloc  int32  // Number of relocation table entries
	Listlen  uint32 // Length of import file ID string table
	Lnimpid  int32  // Number of import file IDs
	Lstlen   uint32 // Length of string table
	Limpoff  uint64 // Offset to start of import file IDs
	Lstoff   uint64 // Offset to start of string table
	Lsymoff  uint64 // Offset to start of symbol table
	Lrldoff  uint64 // Offset to start of relocation entries
}

// Loader Symbol
type XcoffLdSym64 struct {
	Lvalue  uint64 // Address field
	Loffset uint32 // Byte offset into string table of symbol name
	Lscnum  int16  // Section number containing symbol
	Lsmtype int8   // Symbol type, export, import flags
	Lsmclas int8   // Symbol storage class
	Lifile  int32  // Import file ID; ordinal of import file IDs
	Lparm   uint32 // Parameter type-check field
}

type xcoffLoaderSymbol struct {
	sym    *sym.Symbol
	smtype int8
	smclas int8
}

type XcoffLdImportFile64 struct {
	Limpidpath string
	Limpidbase string
	Limpidmem  string
}

type XcoffLdRel64 struct {
	Lvaddr  uint64 // Address Field
	Lrtype  uint16 // Relocation Size and Type
	Lrsecnm int16  // Section Number being relocated
	Lsymndx int32  // Loader-Section symbol table index
}

// xcoffLoaderReloc holds information about a relocation made by the loader.
type xcoffLoaderReloc struct {
	sym    *sym.Symbol
	rel    *sym.Reloc
	rtype  uint16
	symndx int32
}

const (
	XCOFF_R_POS = 0x00 // A(sym) Positive Relocation
)

type XcoffLdStr64 struct {
	size uint16
	name string
}

// xcoffFile is used to build XCOFF file.
type xcoffFile struct {
	xfhdr           XcoffFileHdr64
	xahdr           XcoffAoutHdr64
	sections        []*XcoffScnHdr64
	stringTable     xcoffStringTable
	sectNameToScnum map[string]int16
	loaderSize      uint64
	symtabOffset    int64                // offset to the start of symbol table
	symbolCount     uint32               // number of symbol table records written
	dynLibraries    map[string]int       // Dynamic libraries in .loader section. The integer represents its import file number (- 1)
	loaderSymbols   []*xcoffLoaderSymbol // symbols inside .loader symbol table
	loaderReloc     []*xcoffLoaderReloc  // Reloc that must be made inside loader
}

// Var used by XCOFF Generation algorithms
var (
	xfile xcoffFile
)

// xcoffStringTable is a XCOFF string table.
type xcoffStringTable struct {
	strings    []string
	stringsLen int
}

// size returns size of string table t.
func (t *xcoffStringTable) 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 *xcoffStringTable) 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 *xcoffStringTable) write(out *OutBuf) {
	out.Write32(uint32(t.size()))
	for _, s := range t.strings {
		out.WriteString(s)
		out.Write8(0)
	}
}

// write writes XCOFF section sect into the output file.
func (sect *XcoffScnHdr64) write(ctxt *Link) {
	binary.Write(ctxt.Out, binary.BigEndian, sect)
	ctxt.Out.Write32(0) // Add 4 empty bytes at the end to match alignment
}

// addSection adds section to the XCOFF file f.
func (f *xcoffFile) addSection(name string, addr uint64, size uint64, fileoff uint64, flags uint32) *XcoffScnHdr64 {
	sect := &XcoffScnHdr64{
		Spaddr:  addr,
		Svaddr:  addr,
		Ssize:   size,
		Sscnptr: fileoff,
		Sflags:  flags,
	}
	copy(sect.Sname[:], name) // copy string to [8]byte
	f.sections = append(f.sections, sect)
	f.sectNameToScnum[name] = int16(len(f.sections))
	return sect
}

// addDwarfSection adds a dwarf section to the XCOFF file f.
// This function is similar to addSection, but Dwarf section names
// must be modified to conventional names and they are various subtypes.
func (f *xcoffFile) addDwarfSection(s *sym.Section) *XcoffScnHdr64 {
	newName, subtype := xcoffGetDwarfSubtype(s.Name)
	return f.addSection(newName, 0, s.Length, s.Seg.Fileoff+s.Vaddr-s.Seg.Vaddr, STYP_DWARF|subtype)
}

// xcoffGetDwarfSubtype returns the XCOFF name of the DWARF section str
// and its subtype constant.
func xcoffGetDwarfSubtype(str string) (string, uint32) {
	switch str {
	default:
		Exitf("unknown DWARF section name for XCOFF: %s", str)
	case ".debug_abbrev":
		return ".dwabrev", SSUBTYP_DWABREV
	case ".debug_info":
		return ".dwinfo", SSUBTYP_DWINFO
	case ".debug_frame":
		return ".dwframe", SSUBTYP_DWFRAME
	case ".debug_line":
		return ".dwline", SSUBTYP_DWLINE
	case ".debug_loc":
		return ".dwloc", SSUBTYP_DWLOC
	case ".debug_pubnames":
		return ".dwpbnms", SSUBTYP_DWPBNMS
	case ".debug_pubtypes":
		return ".dwpbtyp", SSUBTYP_DWPBTYP
	case ".debug_ranges":
		return ".dwrnge", SSUBTYP_DWRNGES
	}
	// never used
	return "", 0
}

// getXCOFFscnum returns the XCOFF section number of a Go section.
func (f *xcoffFile) getXCOFFscnum(sect *sym.Section) int16 {
	switch sect.Seg {
	case &Segtext:
		return f.sectNameToScnum[".text"]
	case &Segdata:
		if sect.Name == ".noptrdata" || sect.Name == ".data" {
			return f.sectNameToScnum[".data"]
		}
		if sect.Name == ".noptrbss" || sect.Name == ".bss" {
			return f.sectNameToScnum[".bss"]
		}
		Errorf(nil, "unknown XCOFF segment data section: %s", sect.Name)
	case &Segdwarf:
		name, _ := xcoffGetDwarfSubtype(sect.Name)
		return f.sectNameToScnum[name]
	}
	Errorf(nil, "getXCOFFscnum not implemented for section %s", sect.Name)
	return -1
}

// Xcoffinit initialised some internal value and setups
// already known header information
func Xcoffinit(ctxt *Link) {
	xfile.dynLibraries = make(map[string]int)

	HEADR = int32(Rnd(XCOFFHDRRESERVE, XCOFFSECTALIGN))
	if *FlagTextAddr != -1 {
		Errorf(nil, "-T not available on AIX")
	}
	*FlagTextAddr = XCOFFTEXTBASE + int64(HEADR)
	*FlagDataAddr = 0
	if *FlagRound != -1 {
		Errorf(nil, "-R not available on AIX")
	}
	*FlagRound = int(XCOFFSECTALIGN)

}

// SYMBOL TABLE

// type records C_FILE information needed for genasmsym in XCOFF.
type xcoffSymSrcFile struct {
	name       string
	fileSymNb  uint32 // Symbol number of this C_FILE
	csectSymNb uint64 // Symbol number for the current .csect
	csectSize  int64
}

var (
	currDwscnoff   = make(map[string]uint64) // Needed to create C_DWARF symbols
	currSymSrcFile xcoffSymSrcFile
)

// writeSymbol writes a symbol or an auxiliary symbol entry on ctxt.out.
func (f *xcoffFile) writeSymbol(out *OutBuf, byteOrder binary.ByteOrder, sym interface{}) {
	binary.Write(out, byteOrder, sym)
	f.symbolCount++
}

// Write symbols needed when a new file appared :
// - a C_FILE with one auxiliary entry for its name
// - C_DWARF symbols to provide debug information
// - a C_HIDEXT which will be a csect containing all of its functions
// It needs several parameters to create .csect symbols such as its entry point and its section number.
//
// Currently, a new file is in fact a new package. It seems to be OK, but it might change
// in the future.
func (f *xcoffFile) writeSymbolNewFile(ctxt *Link, name string, firstEntry uint64, extnum int16) {
	/* C_FILE */
	s := &XcoffSymEnt64{
		Noffset: uint32(f.stringTable.add(".file")),
		Nsclass: C_FILE,
		Nscnum:  N_DEBUG,
		Ntype:   0, // Go isn't inside predefined language.
		Nnumaux: 1,
	}
	f.writeSymbol(ctxt.Out, ctxt.Arch.ByteOrder, s)

	// Auxiliary entry for file name.
	ctxt.Out.Write32(0)
	ctxt.Out.Write32(uint32(f.stringTable.add(name)))
	ctxt.Out.Write32(0) // 6 bytes empty
	ctxt.Out.Write16(0)
	ctxt.Out.Write8(XFT_FN)
	ctxt.Out.Write16(0) // 2 bytes empty
	ctxt.Out.Write8(_AUX_FILE)
	f.symbolCount++

	/* Dwarf */
	for _, sect := range Segdwarf.Sections {
		// Find the size of this corresponding package DWARF compilation unit.
		// This size is set during DWARF generation (see dwarf.go).
		dwsize := getDwsectCUSize(sect.Name, name)
		// .debug_abbrev is commun to all packages and not found with the previous function
		if sect.Name == ".debug_abbrev" {
			s := ctxt.Syms.Lookup(sect.Name, 0)
			dwsize = uint64(s.Size)
		}

		// get XCOFF name
		name, _ := xcoffGetDwarfSubtype(sect.Name)
		s := &XcoffSymEnt64{
			Nvalue:  currDwscnoff[sect.Name],
			Noffset: uint32(f.stringTable.add(name)),
			Nsclass: C_DWARF,
			Nscnum:  f.getXCOFFscnum(sect),
			Nnumaux: 1,
		}
		f.writeSymbol(ctxt.Out, ctxt.Arch.ByteOrder, s)

		// update the DWARF section offset in this file
		if sect.Name != ".debug_abbrev" {
			currDwscnoff[sect.Name] += dwsize
		}

		// Auxiliary dwarf section
		ctxt.Out.Write64(dwsize) // section length
		ctxt.Out.Write64(0)      // nreloc
		ctxt.Out.Write8(0)       // pad
		ctxt.Out.Write8(_AUX_SECT)
		f.symbolCount++
	}

	/* .csect */
	// Check if extnum is in text.
	// This is temporary and only here to check if this algorithm is correct.
	if extnum != 1 {
		Exitf("XCOFF symtab: A new file was detected with its first symbol not in .text")
	}

	currSymSrcFile.csectSymNb = uint64(f.symbolCount)
	currSymSrcFile.csectSize = 0

	// No offset because no name
	s = &XcoffSymEnt64{
		Nvalue:  firstEntry,
		Nscnum:  extnum,
		Nsclass: C_HIDEXT,
		Ntype:   0, // check visibility ?
		Nnumaux: 1,
	}
	f.writeSymbol(ctxt.Out, ctxt.Arch.ByteOrder, s)

	aux := &XcoffAuxCSect64{
		Xsmclas:  XMC_PR,
		Xsmtyp:   XTY_SD | 5<<3, // align = 5
		Xauxtype: _AUX_CSECT,
	}
	f.writeSymbol(ctxt.Out, ctxt.Arch.ByteOrder, aux)

}

// Update values for the previous package.
//  - Svalue of the C_FILE symbol: if it is the last one, this Svalue must be -1
//  - Xsclen of the csect symbol.
func (f *xcoffFile) updatePreviousFile(ctxt *Link, last bool) {
	// first file
	if currSymSrcFile.fileSymNb == 0 {
		return
	}

	prevOff := f.symtabOffset + int64(currSymSrcFile.fileSymNb*SYMESZ)
	currOff := ctxt.Out.Offset()

	// Update C_FILE
	ctxt.Out.SeekSet(prevOff)
	if last {
		ctxt.Out.Write64(0xFFFFFFFFFFFFFFFF)
	} else {
		ctxt.Out.Write64(uint64(f.symbolCount))
	}

	// update csect scnlen in this auxiliary entry
	prevOff = f.symtabOffset + int64((currSymSrcFile.csectSymNb+1)*SYMESZ)
	ctxt.Out.SeekSet(prevOff)
	ctxt.Out.Write32(uint32(currSymSrcFile.csectSize & 0xFFFFFFFF))
	prevOff += 12
	ctxt.Out.SeekSet(prevOff)
	ctxt.Out.Write32(uint32(currSymSrcFile.csectSize >> 32))

	ctxt.Out.SeekSet(currOff)

}

// Write symbol representing a .text function.
// The symbol table is split with C_FILE corresponding to each package
// and not to each source file as it should be.
func (f *xcoffFile) writeSymbolFunc(ctxt *Link, x *sym.Symbol) []interface{} {
	// New XCOFF symbols which will be written.
	syms := []interface{}{}

	// Check if a new file is detected.
	if x.File == "" { // Undefined global symbol
		// If this happens, the algorithme must be redone.
		if currSymSrcFile.name != "" {
			Exitf("undefined global symbol found inside another file")
		}
	} else {
		// Current file has changed. New C_FILE, C_DWARF, etc must be generated.
		if currSymSrcFile.name != x.File {
			// update previous file values
			xfile.updatePreviousFile(ctxt, false)
			currSymSrcFile.name = x.File
			currSymSrcFile.fileSymNb = f.symbolCount
			f.writeSymbolNewFile(ctxt, x.File, uint64(x.Value), xfile.getXCOFFscnum(x.Sect))
		}
	}

	s := &XcoffSymEnt64{
		Nsclass: C_EXT,
		Noffset: uint32(xfile.stringTable.add(x.Name)),
		Nvalue:  uint64(x.Value),
		Nscnum:  f.getXCOFFscnum(x.Sect),
		Ntype:   SYM_TYPE_FUNC,
		Nnumaux: 2,
	}

	if x.Version != 0 || x.Attr.VisibilityHidden() || x.Attr.Local() {
		s.Nsclass = C_HIDEXT
	}

	syms = append(syms, s)

	// Update current csect size
	currSymSrcFile.csectSize += x.Size

	// create auxiliary entries
	a2 := &XcoffAuxFcn64{
		Xfsize:   uint32(x.Size),
		Xlnnoptr: 0,                     // TODO
		Xendndx:  xfile.symbolCount + 3, // this symbol + 2 aux entries
		Xauxtype: _AUX_FCN,
	}
	syms = append(syms, a2)

	a4 := &XcoffAuxCSect64{
		Xscnlenlo: uint32(currSymSrcFile.csectSymNb & 0xFFFFFFFF),
		Xscnlenhi: uint32(currSymSrcFile.csectSymNb >> 32),
		Xsmclas:   XMC_PR, // Program Code
		Xsmtyp:    XTY_LD, // label definition (based on C)
		Xauxtype:  _AUX_CSECT,
	}
	syms = append(syms, a4)
	return syms
}

// put function used by genasmsym to write symbol table
func putaixsym(ctxt *Link, x *sym.Symbol, str string, t SymbolType, addr int64, go_ *sym.Symbol) {

	// All XCOFF symbols generated by this GO symbols
	// Can be a symbol entry or a auxiliary entry
	syms := []interface{}{}

	switch t {
	default:
		return

	case TextSym:
		if x.FuncInfo != nil {
			// Function within a file
			syms = xfile.writeSymbolFunc(ctxt, x)
		} else {
			// Only runtime.text and runtime.etext come through this way
			if x.Name != "runtime.text" && x.Name != "runtime.etext" && x.Name != "go.buildid" {
				Exitf("putaixsym: unknown text symbol %s", x.Name)
			}
			s := &XcoffSymEnt64{
				Nsclass: C_HIDEXT,
				Noffset: uint32(xfile.stringTable.add(str)),
				Nvalue:  uint64(x.Value),
				Nscnum:  xfile.getXCOFFscnum(x.Sect),
				Ntype:   SYM_TYPE_FUNC,
				Nnumaux: 1,
			}
			syms = append(syms, s)

			size := uint64(x.Size)
			a4 := &XcoffAuxCSect64{
				Xauxtype:  _AUX_CSECT,
				Xscnlenlo: uint32(size & 0xFFFFFFFF),
				Xscnlenhi: uint32(size >> 32),
				Xsmclas:   XMC_PR,
				Xsmtyp:    XTY_SD,
			}
			syms = append(syms, a4)

		}

	case DataSym, BSSSym:
		s := &XcoffSymEnt64{
			Nsclass: C_EXT,
			Noffset: uint32(xfile.stringTable.add(str)),
			Nvalue:  uint64(x.Value),
			Nscnum:  xfile.getXCOFFscnum(x.Sect),
			Nnumaux: 1,
		}

		if x.Version != 0 || x.Attr.VisibilityHidden() || x.Attr.Local() {
			// There is more symbols in the case of a global data
			// which are related to the assembly generated
			// to access such symbols.
			// But as Golang as its own way to check if a symbol is
			// global or local (the capital letter), we don't need to
			// implement them yet.
			s.Nsclass = C_HIDEXT
		}

		syms = append(syms, s)

		// Create auxiliary entry

		// Normally, size should be the size of csect containing all
		// the data and bss symbols of one file/package.
		// However, it's easier to just have a csect for each symbol.
		// It might change
		size := uint64(x.Size)
		a4 := &XcoffAuxCSect64{
			Xauxtype:  _AUX_CSECT,
			Xscnlenlo: uint32(size & 0xFFFFFFFF),
			Xscnlenhi: uint32(size >> 32),
		}
		// Read only data
		if x.Type >= sym.STYPE && x.Type <= sym.SPCLNTAB {
			a4.Xsmclas = XMC_RO
		} else {
			a4.Xsmclas = XMC_RW
		}
		if t == DataSym {
			a4.Xsmtyp |= XTY_SD
		} else {
			a4.Xsmtyp |= XTY_CM
		}

		syms = append(syms, a4)

	case UndefinedSym:
		if x.Type != sym.SDYNIMPORT && x.Type != sym.SHOSTOBJ {
			return
		}
		s := &XcoffSymEnt64{
			Nsclass: C_EXT,
			Noffset: uint32(xfile.stringTable.add(str)),
			Nnumaux: 1,
		}
		syms = append(syms, s)

		a4 := &XcoffAuxCSect64{
			Xauxtype: _AUX_CSECT,
			Xsmclas:  XMC_DS,
			Xsmtyp:   XTY_ER | XTY_IMP,
		}

		if x.Name == "__n_pthreads" {
			// Currently, all imported symbols made by cgo_import_dynamic are
			// syscall functions, except __n_pthreads which is a variable.
			// TODO(aix): Find a way to detect variables imported by cgo.
			a4.Xsmclas = XMC_RW
		}

		syms = append(syms, a4)
	}

	for _, s := range syms {
		xfile.writeSymbol(ctxt.Out, ctxt.Arch.ByteOrder, s)
	}
}

// Generate XCOFF Symbol table and XCOFF String table
func (f *xcoffFile) asmaixsym(ctxt *Link) {
	// write symbol table
	genasmsym(ctxt, putaixsym)

	// update last file Svalue
	xfile.updatePreviousFile(ctxt, true)

	// write string table
	xfile.stringTable.write(ctxt.Out)
}

func (f *xcoffFile) genDynSym(ctxt *Link) {
	var dynsyms []*sym.Symbol
	for _, s := range ctxt.Syms.Allsym {
		if s.Type != sym.SHOSTOBJ && s.Type != sym.SDYNIMPORT {
			continue
		}
		dynsyms = append(dynsyms, s)
	}

	for _, s := range dynsyms {
		f.adddynimpsym(ctxt, s)

		if _, ok := f.dynLibraries[s.Dynimplib()]; !ok {
			f.dynLibraries[s.Dynimplib()] = len(f.dynLibraries)
		}

	}

}

// (*xcoffFile)adddynimpsym adds the dynamic symbol "s" to a XCOFF file.
// A new symbol named s.Extname() is created to be the actual dynamic symbol
// in the .loader section and in the symbol table as an External Reference.
// The symbol "s" is transformed to SXCOFFTOC to end up in .data section.
// However, there is no writing protection on those symbols and
// it might need to be added.
// TODO(aix): Handles dynamic symbols without library.
func (f *xcoffFile) adddynimpsym(ctxt *Link, s *sym.Symbol) {
	// Check that library name is given.
	// Pattern is already checked when compiling.
	if s.Dynimplib() == "" {
		Errorf(s, "imported symbol must have a given library")
	}

	s.Type = sym.SXCOFFTOC

	// Create new dynamic symbol
	extsym := ctxt.Syms.Lookup(s.Extname(), 0)
	extsym.Type = sym.SDYNIMPORT
	extsym.Attr |= sym.AttrReachable
	extsym.SetDynimplib(s.Dynimplib())
	extsym.SetExtname(s.Extname())
	extsym.SetDynimpvers(s.Dynimpvers())

	// Add loader symbol
	lds := &xcoffLoaderSymbol{
		sym:    extsym,
		smtype: XTY_IMP,
		smclas: XMC_DS,
	}
	if s.Name == "__n_pthreads" {
		// Currently, all imported symbols made by cgo_import_dynamic are
		// syscall functions, except __n_pthreads which is a variable.
		// TODO(aix): Find a way to detect variables imported by cgo.
		lds.smclas = XMC_RW
	}
	f.loaderSymbols = append(f.loaderSymbols, lds)

	// Relocation to retrieve the external address
	s.AddBytes(make([]byte, 8))
	s.SetAddr(ctxt.Arch, 0, extsym)

}

// Xcoffadddynrel adds a dynamic relocation in a XCOFF file.
// This relocation will be made by the loader.
func Xcoffadddynrel(ctxt *Link, s *sym.Symbol, r *sym.Reloc) bool {
	if s.Type <= sym.SPCLNTAB {
		Errorf(s, "cannot have a relocation to %s in a text section symbol", r.Sym.Name)
		return false
	}

	ldr := &xcoffLoaderReloc{
		sym: s,
		rel: r,
	}

	switch r.Type {
	default:
		Errorf(s, "unexpected .loader relocation to symbol: %s (type: %s)", r.Sym.Name, r.Type.String())
		return false
	case objabi.R_ADDR:
		if s.Type == sym.SXCOFFTOC && r.Sym.Type == sym.SDYNIMPORT {
			// Imported symbol relocation
			for i, dynsym := range xfile.loaderSymbols {
				if dynsym.sym.Name == r.Sym.Name {
					ldr.symndx = int32(i + 3) // +3 because of 3 section symbols
					break
				}
			}
		} else if s.Type == sym.SDATA {
			switch r.Sym.Sect.Seg {
			default:
				Errorf(s, "unknown segment for .loader relocation with symbol %s", r.Sym.Name)
			case &Segtext:
			case &Segrodata:
				ldr.symndx = 0 // .text
			case &Segdata:
				if r.Sym.Type == sym.SBSS || r.Sym.Type == sym.SNOPTRBSS {
					ldr.symndx = 2 // .bss
				} else {
					ldr.symndx = 1 // .data
				}

			}

		} else {
			Errorf(s, "unexpected type for .loader relocation R_ADDR for symbol %s: %s to %s", r.Sym.Name, s.Type, r.Sym.Type)
			return false
		}

		ldr.rtype = 0x3F<<8 + XCOFF_R_POS
	}

	xfile.loaderReloc = append(xfile.loaderReloc, ldr)
	return true
}

func (ctxt *Link) doxcoff() {
	if *FlagD {
		// All XCOFF files have dynamic symbols because of the syscalls.
		Exitf("-d is not available on AIX")
	}

	// Initial map used to store compilation unit size for each DWARF section (see dwarf.go).
	dwsectCUSize = make(map[string]uint64)

	// TOC
	toc := ctxt.Syms.Lookup("TOC", 0)
	toc.Type = sym.SXCOFFTOC
	toc.Attr |= sym.AttrReachable

	// XCOFF does not allow relocations of data symbol address to a text symbol.
	// Such case occurs when a RODATA symbol retrieves a data symbol address.
	// When it happens, this RODATA symbol is moved to .data section.
	// runtime.algarray is a readonly symbol but stored inside .data section.
	// If it stays in .data, all type symbols will be moved to .data which
	// cannot be done.
	algarray := ctxt.Syms.Lookup("runtime.algarray", 0)
	algarray.Type = sym.SRODATA
	for {
		again := false
		for _, s := range ctxt.Syms.Allsym {
			if s.Type != sym.SRODATA {
				continue
			}
			for ri := range s.R {
				r := &s.R[ri]
				if r.Type != objabi.R_ADDR {
					continue
				}
				if r.Sym.Type != sym.Sxxx && r.Sym.Type != sym.STEXT && r.Sym.Type != sym.SRODATA {
					s.Type = sym.SDATA
					again = true
					break
				}
			}

		}
		if !again {
			break
		}
	}

	// Add entry point to .loader symbols.
	ep := ctxt.Syms.ROLookup(*flagEntrySymbol, 0)
	if !ep.Attr.Reachable() {
		Exitf("wrong entry point")
	}
	xfile.loaderSymbols = append(xfile.loaderSymbols, &xcoffLoaderSymbol{
		sym:    ep,
		smtype: XTY_ENT | XTY_SD,
		smclas: XMC_DS,
	})

	xfile.genDynSym(ctxt)

	for _, s := range ctxt.Syms.Allsym {
		if strings.HasPrefix(s.Name, "TOC.") {
			s.Type = sym.SXCOFFTOC
		}
	}
}

// Loader section
// Currently, this section is created from scratch when assembling the XCOFF file
// according to information retrieved in xfile object.

// Create loader section and returns its size
func Loaderblk(ctxt *Link, off uint64) {
	xfile.writeLdrScn(ctxt, off)
}

func (f *xcoffFile) writeLdrScn(ctxt *Link, globalOff uint64) {
	var symtab []*XcoffLdSym64
	var strtab []*XcoffLdStr64
	var importtab []*XcoffLdImportFile64
	var reloctab []*XcoffLdRel64
	var dynimpreloc []*XcoffLdRel64

	// As the string table is updated in any loader subsection,
	//  its length must be computed at the same time.
	stlen := uint32(0)

	// Loader Header
	hdr := &XcoffLdHdr64{
		Lversion: 2,
		Lsymoff:  LDHDRSZ_64,
	}

	/* Symbol table */
	for _, s := range f.loaderSymbols {
		lds := &XcoffLdSym64{
			Loffset: uint32(stlen + 2),
			Lsmtype: s.smtype,
			Lsmclas: s.smclas,
		}
		switch s.smtype {
		default:
			Errorf(s.sym, "unexpected loader symbol type: 0x%x", s.smtype)
		case XTY_ENT | XTY_SD:
			lds.Lvalue = uint64(s.sym.Value)
			lds.Lscnum = f.getXCOFFscnum(s.sym.Sect)
		case XTY_IMP:
			lds.Lifile = int32(f.dynLibraries[s.sym.Dynimplib()] + 1)
		}
		ldstr := &XcoffLdStr64{
			size: uint16(len(s.sym.Name) + 1), // + null terminator
			name: s.sym.Name,
		}
		stlen += uint32(2 + ldstr.size) // 2 = sizeof ldstr.size
		symtab = append(symtab, lds)
		strtab = append(strtab, ldstr)

	}

	hdr.Lnsyms = int32(len(symtab))
	hdr.Lrldoff = hdr.Lsymoff + uint64(24*hdr.Lnsyms) // 24 = sizeof one symbol
	off := hdr.Lrldoff                                // current offset is the same of reloc offset

	/* Reloc */
	ep := ctxt.Syms.ROLookup(*flagEntrySymbol, 0)
	ldr := &XcoffLdRel64{
		Lvaddr:  uint64(ep.Value),
		Lrtype:  0x3F00,
		Lrsecnm: f.getXCOFFscnum(ep.Sect),
		Lsymndx: 0,
	}
	off += 16
	reloctab = append(reloctab, ldr)

	off += uint64(16 * len(f.loaderReloc))
	for _, r := range f.loaderReloc {
		ldr = &XcoffLdRel64{
			Lvaddr:  uint64(r.sym.Value + int64(r.rel.Off)),
			Lrtype:  r.rtype,
			Lsymndx: r.symndx,
		}

		if r.sym.Sect != nil {
			ldr.Lrsecnm = f.getXCOFFscnum(r.sym.Sect)
		}

		reloctab = append(reloctab, ldr)
	}

	off += uint64(16 * len(dynimpreloc))
	reloctab = append(reloctab, dynimpreloc...)

	hdr.Lnreloc = int32(len(reloctab))
	hdr.Limpoff = off

	/* Import */
	// Default import: /usr/lib:/lib
	ldimpf := &XcoffLdImportFile64{
		Limpidpath: "/usr/lib:/lib",
	}
	off += uint64(len(ldimpf.Limpidpath) + len(ldimpf.Limpidbase) + len(ldimpf.Limpidmem) + 3) // + null delimiter
	importtab = append(importtab, ldimpf)

	// The map created by adddynimpsym associates the name to a number
	// This number represents the librairie index (- 1) in this import files section
	// Therefore, they must be sorted before being put inside the section
	libsOrdered := make([]string, len(f.dynLibraries))
	for key, val := range f.dynLibraries {
		if libsOrdered[val] != "" {
			continue
		}
		libsOrdered[val] = key
	}

	for _, lib := range libsOrdered {
		// lib string is defined as base.a/mem.o or path/base.a/mem.o
		n := strings.Split(lib, "/")
		path := ""
		base := n[len(n)-2]
		mem := n[len(n)-1]
		if len(n) > 2 {
			path = lib[:len(lib)-len(base)-len(mem)-2]

		}
		ldimpf = &XcoffLdImportFile64{
			Limpidpath: path,
			Limpidbase: base,
			Limpidmem:  mem,
		}
		off += uint64(len(ldimpf.Limpidpath) + len(ldimpf.Limpidbase) + len(ldimpf.Limpidmem) + 3) // + null delimiter
		importtab = append(importtab, ldimpf)
	}

	hdr.Lnimpid = int32(len(importtab))
	hdr.Listlen = uint32(off - hdr.Limpoff)
	hdr.Lstoff = off
	hdr.Lstlen = stlen

	/* Writing */
	ctxt.Out.SeekSet(int64(globalOff))
	binary.Write(ctxt.Out, ctxt.Arch.ByteOrder, hdr)

	for _, s := range symtab {
		binary.Write(ctxt.Out, ctxt.Arch.ByteOrder, s)

	}
	for _, r := range reloctab {
		binary.Write(ctxt.Out, ctxt.Arch.ByteOrder, r)
	}
	for _, f := range importtab {
		ctxt.Out.WriteString(f.Limpidpath)
		ctxt.Out.Write8(0)
		ctxt.Out.WriteString(f.Limpidbase)
		ctxt.Out.Write8(0)
		ctxt.Out.WriteString(f.Limpidmem)
		ctxt.Out.Write8(0)
	}
	for _, s := range strtab {
		ctxt.Out.Write16(s.size)
		ctxt.Out.WriteString(s.name)
		ctxt.Out.Write8(0) // null terminator
	}

	f.loaderSize = off + uint64(stlen)
	ctxt.Out.Flush()

	/* again for printing */
	if !*flagA {
		return
	}

	ctxt.Logf("\n.loader section")
	// write in buf
	var buf bytes.Buffer

	binary.Write(&buf, ctxt.Arch.ByteOrder, hdr)
	for _, s := range symtab {
		binary.Write(&buf, ctxt.Arch.ByteOrder, s)

	}
	for _, f := range importtab {
		buf.WriteString(f.Limpidpath)
		buf.WriteByte(0)
		buf.WriteString(f.Limpidbase)
		buf.WriteByte(0)
		buf.WriteString(f.Limpidmem)
		buf.WriteByte(0)
	}
	for _, s := range strtab {
		binary.Write(&buf, ctxt.Arch.ByteOrder, s.size)
		buf.WriteString(s.name)
		buf.WriteByte(0) // null terminator
	}

	// Log buffer
	ctxt.Logf("\n\t%.8x|", globalOff)
	for i, b := range buf.Bytes() {
		if i > 0 && i%16 == 0 {
			ctxt.Logf("\n\t%.8x|", uint64(globalOff)+uint64(i))
		}
		ctxt.Logf(" %.2x", b)
	}
	ctxt.Logf("\n")

}

// XCOFF assembling and writing file

func (f *xcoffFile) writeFileHeader(ctxt *Link) {
	// File header
	f.xfhdr.Fmagic = U64_TOCMAGIC
	f.xfhdr.Fnscns = uint16(len(f.sections))
	f.xfhdr.Ftimedat = 0

	if !*FlagS {
		f.xfhdr.Fsymptr = uint64(f.symtabOffset)
		f.xfhdr.Fnsyms = int32(f.symbolCount)
	}

	if ctxt.BuildMode == BuildModeExe {
		f.xfhdr.Fopthdr = AOUTHSZ_EXEC64
		f.xfhdr.Fflags = F_EXEC

		// auxiliary header
		f.xahdr.Ovstamp = 1 // based on dump -o
		f.xahdr.Omagic = 0x10b
		copy(f.xahdr.Omodtype[:], "1L")
		entry := ctxt.Syms.ROLookup(*flagEntrySymbol, 0)
		f.xahdr.Oentry = uint64(entry.Value)
		f.xahdr.Osnentry = f.getXCOFFscnum(entry.Sect)
		toc := ctxt.Syms.ROLookup("TOC", 0)
		f.xahdr.Otoc = uint64(toc.Value)
		f.xahdr.Osntoc = f.getXCOFFscnum(toc.Sect)

		// Based on dump -o
		f.xahdr.Oalgntext = 0x5
		f.xahdr.Oalgndata = 0x5

		binary.Write(ctxt.Out, binary.BigEndian, &f.xfhdr)
		binary.Write(ctxt.Out, binary.BigEndian, &f.xahdr)
	} else {
		f.xfhdr.Fopthdr = 0
		binary.Write(ctxt.Out, binary.BigEndian, &f.xfhdr)
	}

}

func xcoffwrite(ctxt *Link) {
	ctxt.Out.SeekSet(0)

	xfile.writeFileHeader(ctxt)

	for _, sect := range xfile.sections {
		sect.write(ctxt)
	}
}

// Generate XCOFF assembly file
func Asmbxcoff(ctxt *Link, fileoff int64) {
	xfile.sectNameToScnum = make(map[string]int16)

	// Add sections
	s := xfile.addSection(".text", Segtext.Vaddr, Segtext.Length, Segtext.Fileoff, STYP_TEXT)
	xfile.xahdr.Otextstart = s.Svaddr
	xfile.xahdr.Osntext = xfile.sectNameToScnum[".text"]
	xfile.xahdr.Otsize = s.Ssize

	s = xfile.addSection(".data", Segdata.Vaddr, Segdata.Filelen, Segdata.Fileoff, STYP_DATA)
	xfile.xahdr.Odatastart = s.Svaddr
	xfile.xahdr.Osndata = xfile.sectNameToScnum[".data"]
	xfile.xahdr.Odsize = s.Ssize

	s = xfile.addSection(".bss", Segdata.Vaddr+Segdata.Filelen, Segdata.Length-Segdata.Filelen, 0, STYP_BSS)
	xfile.xahdr.Osnbss = xfile.sectNameToScnum[".bss"]
	xfile.xahdr.Obsize = s.Ssize

	// add dwarf sections
	for _, sect := range Segdwarf.Sections {
		xfile.addDwarfSection(sect)
	}

	// add and write remaining sections
	if ctxt.LinkMode == LinkInternal {
		// Loader section
		if ctxt.BuildMode == BuildModeExe {
			Loaderblk(ctxt, uint64(fileoff))
			s = xfile.addSection(".loader", 0, xfile.loaderSize, uint64(fileoff), STYP_LOADER)
			xfile.xahdr.Osnloader = xfile.sectNameToScnum[".loader"]
		}
	} else {
		// TODO: Relocation
	}

	// Write symbol table
	symo := Rnd(ctxt.Out.Offset(), int64(*FlagRound))
	xfile.symtabOffset = symo
	ctxt.Out.SeekSet(int64(symo))
	xfile.asmaixsym(ctxt)

	// write headers
	xcoffwrite(ctxt)
}