Current File : //usr/local/go/src/cmd/link/internal/ld/pcln.go
// Copyright 2013 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 (
"cmd/internal/goobj"
"cmd/internal/objabi"
"cmd/internal/sys"
"cmd/link/internal/loader"
"cmd/link/internal/sym"
"fmt"
"internal/buildcfg"
"os"
"path/filepath"
)
// pclntab holds the state needed for pclntab generation.
type pclntab struct {
// The size of the func object in the runtime.
funcSize uint32
// The first and last functions found.
firstFunc, lastFunc loader.Sym
// Running total size of pclntab.
size int64
// runtime.pclntab's symbols
carrier loader.Sym
pclntab loader.Sym
pcheader loader.Sym
funcnametab loader.Sym
findfunctab loader.Sym
cutab loader.Sym
filetab loader.Sym
pctab loader.Sym
// The number of functions + number of TEXT sections - 1. This is such an
// unexpected value because platforms that have more than one TEXT section
// get a dummy function inserted between because the external linker can place
// functions in those areas. We mark those areas as not covered by the Go
// runtime.
//
// On most platforms this is the number of reachable functions.
nfunc int32
// The number of filenames in runtime.filetab.
nfiles uint32
}
// addGeneratedSym adds a generator symbol to pclntab, returning the new Sym.
// It is the caller's responsibility to save they symbol in state.
func (state *pclntab) addGeneratedSym(ctxt *Link, name string, size int64, f generatorFunc) loader.Sym {
size = Rnd(size, int64(ctxt.Arch.PtrSize))
state.size += size
s := ctxt.createGeneratorSymbol(name, 0, sym.SPCLNTAB, size, f)
ctxt.loader.SetAttrReachable(s, true)
ctxt.loader.SetCarrierSym(s, state.carrier)
ctxt.loader.SetAttrNotInSymbolTable(s, true)
return s
}
// makePclntab makes a pclntab object, and assembles all the compilation units
// we'll need to write pclntab. Returns the pclntab structure, a slice of the
// CompilationUnits we need, and a slice of the function symbols we need to
// generate pclntab.
func makePclntab(ctxt *Link, container loader.Bitmap) (*pclntab, []*sym.CompilationUnit, []loader.Sym) {
ldr := ctxt.loader
state := &pclntab{
// This is the size of the _func object in runtime/runtime2.go.
funcSize: uint32(ctxt.Arch.PtrSize + 9*4),
}
// Gather some basic stats and info.
seenCUs := make(map[*sym.CompilationUnit]struct{})
prevSect := ldr.SymSect(ctxt.Textp[0])
compUnits := []*sym.CompilationUnit{}
funcs := []loader.Sym{}
for _, s := range ctxt.Textp {
if !emitPcln(ctxt, s, container) {
continue
}
funcs = append(funcs, s)
state.nfunc++
if state.firstFunc == 0 {
state.firstFunc = s
}
state.lastFunc = s
ss := ldr.SymSect(s)
if ss != prevSect {
// With multiple text sections, the external linker may
// insert functions between the sections, which are not
// known by Go. This leaves holes in the PC range covered
// by the func table. We need to generate an entry to mark
// the hole.
state.nfunc++
prevSect = ss
}
// We need to keep track of all compilation units we see. Some symbols
// (eg, go.buildid, _cgoexp_, etc) won't have a compilation unit.
cu := ldr.SymUnit(s)
if _, ok := seenCUs[cu]; cu != nil && !ok {
seenCUs[cu] = struct{}{}
cu.PclnIndex = len(compUnits)
compUnits = append(compUnits, cu)
}
}
return state, compUnits, funcs
}
func emitPcln(ctxt *Link, s loader.Sym, container loader.Bitmap) bool {
// We want to generate func table entries only for the "lowest
// level" symbols, not containers of subsymbols.
return !container.Has(s)
}
func computeDeferReturn(ctxt *Link, deferReturnSym, s loader.Sym) uint32 {
ldr := ctxt.loader
target := ctxt.Target
deferreturn := uint32(0)
lastWasmAddr := uint32(0)
relocs := ldr.Relocs(s)
for ri := 0; ri < relocs.Count(); ri++ {
r := relocs.At(ri)
if target.IsWasm() && r.Type() == objabi.R_ADDR {
// Wasm does not have a live variable set at the deferreturn
// call itself. Instead it has one identified by the
// resumption point immediately preceding the deferreturn.
// The wasm code has a R_ADDR relocation which is used to
// set the resumption point to PC_B.
lastWasmAddr = uint32(r.Add())
}
if r.Type().IsDirectCall() && (r.Sym() == deferReturnSym || ldr.IsDeferReturnTramp(r.Sym())) {
if target.IsWasm() {
deferreturn = lastWasmAddr - 1
} else {
// Note: the relocation target is in the call instruction, but
// is not necessarily the whole instruction (for instance, on
// x86 the relocation applies to bytes [1:5] of the 5 byte call
// instruction).
deferreturn = uint32(r.Off())
switch target.Arch.Family {
case sys.AMD64, sys.I386:
deferreturn--
case sys.PPC64, sys.ARM, sys.ARM64, sys.MIPS, sys.MIPS64:
// no change
case sys.RISCV64:
// TODO(jsing): The JALR instruction is marked with
// R_CALLRISCV, whereas the actual reloc is currently
// one instruction earlier starting with the AUIPC.
deferreturn -= 4
case sys.S390X:
deferreturn -= 2
default:
panic(fmt.Sprint("Unhandled architecture:", target.Arch.Family))
}
}
break // only need one
}
}
return deferreturn
}
// genInlTreeSym generates the InlTree sym for a function with the
// specified FuncInfo.
func genInlTreeSym(ctxt *Link, cu *sym.CompilationUnit, fi loader.FuncInfo, arch *sys.Arch, nameOffsets map[loader.Sym]uint32) loader.Sym {
ldr := ctxt.loader
its := ldr.CreateExtSym("", 0)
inlTreeSym := ldr.MakeSymbolUpdater(its)
// Note: the generated symbol is given a type of sym.SGOFUNC, as a
// signal to the symtab() phase that it needs to be grouped in with
// other similar symbols (gcdata, etc); the dodata() phase will
// eventually switch the type back to SRODATA.
inlTreeSym.SetType(sym.SGOFUNC)
ldr.SetAttrReachable(its, true)
ninl := fi.NumInlTree()
for i := 0; i < int(ninl); i++ {
call := fi.InlTree(i)
val := call.File
nameoff, ok := nameOffsets[call.Func]
if !ok {
panic("couldn't find function name offset")
}
inlTreeSym.SetUint16(arch, int64(i*20+0), uint16(call.Parent))
inlFunc := ldr.FuncInfo(call.Func)
var funcID objabi.FuncID
if inlFunc.Valid() {
funcID = inlFunc.FuncID()
}
inlTreeSym.SetUint8(arch, int64(i*20+2), uint8(funcID))
// byte 3 is unused
inlTreeSym.SetUint32(arch, int64(i*20+4), uint32(val))
inlTreeSym.SetUint32(arch, int64(i*20+8), uint32(call.Line))
inlTreeSym.SetUint32(arch, int64(i*20+12), uint32(nameoff))
inlTreeSym.SetUint32(arch, int64(i*20+16), uint32(call.ParentPC))
}
return its
}
// makeInlSyms returns a map of loader.Sym that are created inlSyms.
func makeInlSyms(ctxt *Link, funcs []loader.Sym, nameOffsets map[loader.Sym]uint32) map[loader.Sym]loader.Sym {
ldr := ctxt.loader
// Create the inline symbols we need.
inlSyms := make(map[loader.Sym]loader.Sym)
for _, s := range funcs {
if fi := ldr.FuncInfo(s); fi.Valid() {
fi.Preload()
if fi.NumInlTree() > 0 {
inlSyms[s] = genInlTreeSym(ctxt, ldr.SymUnit(s), fi, ctxt.Arch, nameOffsets)
}
}
}
return inlSyms
}
// generatePCHeader creates the runtime.pcheader symbol, setting it up as a
// generator to fill in its data later.
func (state *pclntab) generatePCHeader(ctxt *Link) {
writeHeader := func(ctxt *Link, s loader.Sym) {
ldr := ctxt.loader
header := ctxt.loader.MakeSymbolUpdater(s)
writeSymOffset := func(off int64, ws loader.Sym) int64 {
diff := ldr.SymValue(ws) - ldr.SymValue(s)
if diff <= 0 {
name := ldr.SymName(ws)
panic(fmt.Sprintf("expected runtime.pcheader(%x) to be placed before %s(%x)", ldr.SymValue(s), name, ldr.SymValue(ws)))
}
return header.SetUintptr(ctxt.Arch, off, uintptr(diff))
}
// Write header.
// Keep in sync with runtime/symtab.go:pcHeader.
header.SetUint32(ctxt.Arch, 0, 0xfffffffa)
header.SetUint8(ctxt.Arch, 6, uint8(ctxt.Arch.MinLC))
header.SetUint8(ctxt.Arch, 7, uint8(ctxt.Arch.PtrSize))
off := header.SetUint(ctxt.Arch, 8, uint64(state.nfunc))
off = header.SetUint(ctxt.Arch, off, uint64(state.nfiles))
off = writeSymOffset(off, state.funcnametab)
off = writeSymOffset(off, state.cutab)
off = writeSymOffset(off, state.filetab)
off = writeSymOffset(off, state.pctab)
off = writeSymOffset(off, state.pclntab)
}
size := int64(8 + 7*ctxt.Arch.PtrSize)
state.pcheader = state.addGeneratedSym(ctxt, "runtime.pcheader", size, writeHeader)
}
// walkFuncs iterates over the funcs, calling a function for each unique
// function and inlined function.
func walkFuncs(ctxt *Link, funcs []loader.Sym, f func(loader.Sym)) {
ldr := ctxt.loader
seen := make(map[loader.Sym]struct{})
for _, s := range funcs {
if _, ok := seen[s]; !ok {
f(s)
seen[s] = struct{}{}
}
fi := ldr.FuncInfo(s)
if !fi.Valid() {
continue
}
fi.Preload()
for i, ni := 0, fi.NumInlTree(); i < int(ni); i++ {
call := fi.InlTree(i).Func
if _, ok := seen[call]; !ok {
f(call)
seen[call] = struct{}{}
}
}
}
}
// generateFuncnametab creates the function name table. Returns a map of
// func symbol to the name offset in runtime.funcnamtab.
func (state *pclntab) generateFuncnametab(ctxt *Link, funcs []loader.Sym) map[loader.Sym]uint32 {
nameOffsets := make(map[loader.Sym]uint32, state.nfunc)
// Write the null terminated strings.
writeFuncNameTab := func(ctxt *Link, s loader.Sym) {
symtab := ctxt.loader.MakeSymbolUpdater(s)
for s, off := range nameOffsets {
symtab.AddStringAt(int64(off), ctxt.loader.SymName(s))
}
}
// Loop through the CUs, and calculate the size needed.
var size int64
walkFuncs(ctxt, funcs, func(s loader.Sym) {
nameOffsets[s] = uint32(size)
size += int64(ctxt.loader.SymNameLen(s)) + 1 // NULL terminate
})
state.funcnametab = state.addGeneratedSym(ctxt, "runtime.funcnametab", size, writeFuncNameTab)
return nameOffsets
}
// walkFilenames walks funcs, calling a function for each filename used in each
// function's line table.
func walkFilenames(ctxt *Link, funcs []loader.Sym, f func(*sym.CompilationUnit, goobj.CUFileIndex)) {
ldr := ctxt.loader
// Loop through all functions, finding the filenames we need.
for _, s := range funcs {
fi := ldr.FuncInfo(s)
if !fi.Valid() {
continue
}
fi.Preload()
cu := ldr.SymUnit(s)
for i, nf := 0, int(fi.NumFile()); i < nf; i++ {
f(cu, fi.File(i))
}
for i, ninl := 0, int(fi.NumInlTree()); i < ninl; i++ {
call := fi.InlTree(i)
f(cu, call.File)
}
}
}
// generateFilenameTabs creates LUTs needed for filename lookup. Returns a slice
// of the index at which each CU begins in runtime.cutab.
//
// Function objects keep track of the files they reference to print the stack.
// This function creates a per-CU list of filenames if CU[M] references
// files[1-N], the following is generated:
//
// runtime.cutab:
// CU[M]
// offsetToFilename[0]
// offsetToFilename[1]
// ..
//
// runtime.filetab
// filename[0]
// filename[1]
//
// Looking up a filename then becomes:
// 0) Given a func, and filename index [K]
// 1) Get Func.CUIndex: M := func.cuOffset
// 2) Find filename offset: fileOffset := runtime.cutab[M+K]
// 3) Get the filename: getcstring(runtime.filetab[fileOffset])
func (state *pclntab) generateFilenameTabs(ctxt *Link, compUnits []*sym.CompilationUnit, funcs []loader.Sym) []uint32 {
// On a per-CU basis, keep track of all the filenames we need.
//
// Note, that we store the filenames in a separate section in the object
// files, and deduplicate based on the actual value. It would be better to
// store the filenames as symbols, using content addressable symbols (and
// then not loading extra filenames), and just use the hash value of the
// symbol name to do this cataloging.
//
// TODO: Store filenames as symbols. (Note this would be easiest if you
// also move strings to ALWAYS using the larger content addressable hash
// function, and use that hash value for uniqueness testing.)
cuEntries := make([]goobj.CUFileIndex, len(compUnits))
fileOffsets := make(map[string]uint32)
// Walk the filenames.
// We store the total filename string length we need to load, and the max
// file index we've seen per CU so we can calculate how large the
// CU->global table needs to be.
var fileSize int64
walkFilenames(ctxt, funcs, func(cu *sym.CompilationUnit, i goobj.CUFileIndex) {
// Note we use the raw filename for lookup, but use the expanded filename
// when we save the size.
filename := cu.FileTable[i]
if _, ok := fileOffsets[filename]; !ok {
fileOffsets[filename] = uint32(fileSize)
fileSize += int64(len(expandFile(filename)) + 1) // NULL terminate
}
// Find the maximum file index we've seen.
if cuEntries[cu.PclnIndex] < i+1 {
cuEntries[cu.PclnIndex] = i + 1 // Store max + 1
}
})
// Calculate the size of the runtime.cutab variable.
var totalEntries uint32
cuOffsets := make([]uint32, len(cuEntries))
for i, entries := range cuEntries {
// Note, cutab is a slice of uint32, so an offset to a cu's entry is just the
// running total of all cu indices we've needed to store so far, not the
// number of bytes we've stored so far.
cuOffsets[i] = totalEntries
totalEntries += uint32(entries)
}
// Write cutab.
writeCutab := func(ctxt *Link, s loader.Sym) {
sb := ctxt.loader.MakeSymbolUpdater(s)
var off int64
for i, max := range cuEntries {
// Write the per CU LUT.
cu := compUnits[i]
for j := goobj.CUFileIndex(0); j < max; j++ {
fileOffset, ok := fileOffsets[cu.FileTable[j]]
if !ok {
// We're looping through all possible file indices. It's possible a file's
// been deadcode eliminated, and although it's a valid file in the CU, it's
// not needed in this binary. When that happens, use an invalid offset.
fileOffset = ^uint32(0)
}
off = sb.SetUint32(ctxt.Arch, off, fileOffset)
}
}
}
state.cutab = state.addGeneratedSym(ctxt, "runtime.cutab", int64(totalEntries*4), writeCutab)
// Write filetab.
writeFiletab := func(ctxt *Link, s loader.Sym) {
sb := ctxt.loader.MakeSymbolUpdater(s)
// Write the strings.
for filename, loc := range fileOffsets {
sb.AddStringAt(int64(loc), expandFile(filename))
}
}
state.nfiles = uint32(len(fileOffsets))
state.filetab = state.addGeneratedSym(ctxt, "runtime.filetab", fileSize, writeFiletab)
return cuOffsets
}
// generatePctab creates the runtime.pctab variable, holding all the
// deduplicated pcdata.
func (state *pclntab) generatePctab(ctxt *Link, funcs []loader.Sym) {
ldr := ctxt.loader
// Pctab offsets of 0 are considered invalid in the runtime. We respect
// that by just padding a single byte at the beginning of runtime.pctab,
// that way no real offsets can be zero.
size := int64(1)
// Walk the functions, finding offset to store each pcdata.
seen := make(map[loader.Sym]struct{})
saveOffset := func(pcSym loader.Sym) {
if _, ok := seen[pcSym]; !ok {
datSize := ldr.SymSize(pcSym)
if datSize != 0 {
ldr.SetSymValue(pcSym, size)
} else {
// Invalid PC data, record as zero.
ldr.SetSymValue(pcSym, 0)
}
size += datSize
seen[pcSym] = struct{}{}
}
}
for _, s := range funcs {
fi := ldr.FuncInfo(s)
if !fi.Valid() {
continue
}
fi.Preload()
pcSyms := []loader.Sym{fi.Pcsp(), fi.Pcfile(), fi.Pcline()}
for _, pcSym := range pcSyms {
saveOffset(pcSym)
}
for _, pcSym := range fi.Pcdata() {
saveOffset(pcSym)
}
if fi.NumInlTree() > 0 {
saveOffset(fi.Pcinline())
}
}
// TODO: There is no reason we need a generator for this variable, and it
// could be moved to a carrier symbol. However, carrier symbols containing
// carrier symbols don't work yet (as of Aug 2020). Once this is fixed,
// runtime.pctab could just be a carrier sym.
writePctab := func(ctxt *Link, s loader.Sym) {
ldr := ctxt.loader
sb := ldr.MakeSymbolUpdater(s)
for sym := range seen {
sb.SetBytesAt(ldr.SymValue(sym), ldr.Data(sym))
}
}
state.pctab = state.addGeneratedSym(ctxt, "runtime.pctab", size, writePctab)
}
// numPCData returns the number of PCData syms for the FuncInfo.
// NB: Preload must be called on valid FuncInfos before calling this function.
func numPCData(fi loader.FuncInfo) uint32 {
if !fi.Valid() {
return 0
}
numPCData := uint32(len(fi.Pcdata()))
if fi.NumInlTree() > 0 {
if numPCData < objabi.PCDATA_InlTreeIndex+1 {
numPCData = objabi.PCDATA_InlTreeIndex + 1
}
}
return numPCData
}
// Helper types for iterating pclntab.
type pclnSetAddr func(*loader.SymbolBuilder, *sys.Arch, int64, loader.Sym, int64) int64
type pclnSetUint func(*loader.SymbolBuilder, *sys.Arch, int64, uint64) int64
// generateFunctab creates the runtime.functab
//
// runtime.functab contains two things:
//
// - pc->func look up table.
// - array of func objects, interleaved with pcdata and funcdata
//
// Because of timing in the linker, generating this table takes two passes.
// The first pass is executed early in the link, and it creates any needed
// relocations to layout the data. The pieces that need relocations are:
// 1) the PC->func table.
// 2) The entry points in the func objects.
// 3) The funcdata.
// (1) and (2) are handled in walkPCToFunc. (3) is handled in walkFuncdata.
//
// After relocations, once we know where to write things in the output buffer,
// we execute the second pass, which is actually writing the data.
func (state *pclntab) generateFunctab(ctxt *Link, funcs []loader.Sym, inlSyms map[loader.Sym]loader.Sym, cuOffsets []uint32, nameOffsets map[loader.Sym]uint32) {
// Calculate the size of the table.
size, startLocations := state.calculateFunctabSize(ctxt, funcs)
// If we are internally linking a static executable, the function addresses
// are known, so we can just use them instead of emitting relocations. For
// other cases we still need to emit relocations.
//
// This boolean just helps us figure out which callback to use.
useSymValue := ctxt.IsExe() && ctxt.IsInternal()
writePcln := func(ctxt *Link, s loader.Sym) {
ldr := ctxt.loader
sb := ldr.MakeSymbolUpdater(s)
// Create our callbacks.
var setAddr pclnSetAddr
if useSymValue {
// We need to write the offset.
setAddr = func(s *loader.SymbolBuilder, arch *sys.Arch, off int64, tgt loader.Sym, add int64) int64 {
if v := ldr.SymValue(tgt); v != 0 {
s.SetUint(arch, off, uint64(v+add))
}
return 0
}
} else {
// We already wrote relocations.
setAddr = func(s *loader.SymbolBuilder, arch *sys.Arch, off int64, tgt loader.Sym, add int64) int64 { return 0 }
}
// Write the data.
writePcToFunc(ctxt, sb, funcs, startLocations, setAddr, (*loader.SymbolBuilder).SetUint)
writeFuncs(ctxt, sb, funcs, inlSyms, startLocations, cuOffsets, nameOffsets)
state.writeFuncData(ctxt, sb, funcs, inlSyms, startLocations, setAddr, (*loader.SymbolBuilder).SetUint)
}
state.pclntab = state.addGeneratedSym(ctxt, "runtime.functab", size, writePcln)
// Create the relocations we need.
ldr := ctxt.loader
sb := ldr.MakeSymbolUpdater(state.pclntab)
var setAddr pclnSetAddr
if useSymValue {
// If we should use the symbol value, and we don't have one, write a relocation.
setAddr = func(sb *loader.SymbolBuilder, arch *sys.Arch, off int64, tgt loader.Sym, add int64) int64 {
if v := ldr.SymValue(tgt); v == 0 {
sb.SetAddrPlus(arch, off, tgt, add)
}
return 0
}
} else {
// If we're externally linking, write a relocation.
setAddr = (*loader.SymbolBuilder).SetAddrPlus
}
setUintNOP := func(*loader.SymbolBuilder, *sys.Arch, int64, uint64) int64 { return 0 }
writePcToFunc(ctxt, sb, funcs, startLocations, setAddr, setUintNOP)
if !useSymValue {
// Generate relocations for funcdata when externally linking.
state.writeFuncData(ctxt, sb, funcs, inlSyms, startLocations, setAddr, setUintNOP)
sb.SortRelocs()
}
}
// funcData returns the funcdata and offsets for the FuncInfo.
// The funcdata and offsets are written into runtime.functab after each func
// object. This is a helper function to make querying the FuncInfo object
// cleaner.
//
// Note, the majority of fdOffsets are 0, meaning there is no offset between
// the compiler's generated symbol, and what the runtime needs. They are
// plumbed through for no loss of generality.
//
// NB: Preload must be called on the FuncInfo before calling.
// NB: fdSyms and fdOffs are used as scratch space.
func funcData(fi loader.FuncInfo, inlSym loader.Sym, fdSyms []loader.Sym, fdOffs []int64) ([]loader.Sym, []int64) {
fdSyms, fdOffs = fdSyms[:0], fdOffs[:0]
if fi.Valid() {
numOffsets := int(fi.NumFuncdataoff())
for i := 0; i < numOffsets; i++ {
fdOffs = append(fdOffs, fi.Funcdataoff(i))
}
fdSyms = fi.Funcdata(fdSyms)
if fi.NumInlTree() > 0 {
if len(fdSyms) < objabi.FUNCDATA_InlTree+1 {
fdSyms = append(fdSyms, make([]loader.Sym, objabi.FUNCDATA_InlTree+1-len(fdSyms))...)
fdOffs = append(fdOffs, make([]int64, objabi.FUNCDATA_InlTree+1-len(fdOffs))...)
}
fdSyms[objabi.FUNCDATA_InlTree] = inlSym
}
}
return fdSyms, fdOffs
}
// calculateFunctabSize calculates the size of the pclntab, and the offsets in
// the output buffer for individual func entries.
func (state pclntab) calculateFunctabSize(ctxt *Link, funcs []loader.Sym) (int64, []uint32) {
ldr := ctxt.loader
startLocations := make([]uint32, len(funcs))
// Allocate space for the pc->func table. This structure consists of a pc
// and an offset to the func structure. After that, we have a single pc
// value that marks the end of the last function in the binary.
size := int64(int(state.nfunc)*2*ctxt.Arch.PtrSize + ctxt.Arch.PtrSize)
// Now find the space for the func objects. We do this in a running manner,
// so that we can find individual starting locations, and because funcdata
// requires alignment.
for i, s := range funcs {
size = Rnd(size, int64(ctxt.Arch.PtrSize))
startLocations[i] = uint32(size)
fi := ldr.FuncInfo(s)
size += int64(state.funcSize)
if fi.Valid() {
fi.Preload()
numFuncData := int(fi.NumFuncdataoff())
if fi.NumInlTree() > 0 {
if numFuncData < objabi.FUNCDATA_InlTree+1 {
numFuncData = objabi.FUNCDATA_InlTree + 1
}
}
size += int64(numPCData(fi) * 4)
if numFuncData > 0 { // Func data is aligned.
size = Rnd(size, int64(ctxt.Arch.PtrSize))
}
size += int64(numFuncData * ctxt.Arch.PtrSize)
}
}
return size, startLocations
}
// writePcToFunc writes the PC->func lookup table.
// This function walks the pc->func lookup table, executing callbacks
// to generate relocations and writing the values for the table.
func writePcToFunc(ctxt *Link, sb *loader.SymbolBuilder, funcs []loader.Sym, startLocations []uint32, setAddr pclnSetAddr, setUint pclnSetUint) {
ldr := ctxt.loader
var prevFunc loader.Sym
prevSect := ldr.SymSect(funcs[0])
funcIndex := 0
for i, s := range funcs {
if thisSect := ldr.SymSect(s); thisSect != prevSect {
// With multiple text sections, there may be a hole here in the
// address space. We use an invalid funcoff value to mark the hole.
// See also runtime/symtab.go:findfunc
prevFuncSize := int64(ldr.SymSize(prevFunc))
setAddr(sb, ctxt.Arch, int64(funcIndex*2*ctxt.Arch.PtrSize), prevFunc, prevFuncSize)
setUint(sb, ctxt.Arch, int64((funcIndex*2+1)*ctxt.Arch.PtrSize), ^uint64(0))
funcIndex++
prevSect = thisSect
}
prevFunc = s
// TODO: We don't actually need these relocations, provided we go to a
// module->func look-up-table like we do for filenames. We could have a
// single relocation for the module, and have them all laid out as
// offsets from the beginning of that module.
setAddr(sb, ctxt.Arch, int64(funcIndex*2*ctxt.Arch.PtrSize), s, 0)
setUint(sb, ctxt.Arch, int64((funcIndex*2+1)*ctxt.Arch.PtrSize), uint64(startLocations[i]))
funcIndex++
// Write the entry location.
setAddr(sb, ctxt.Arch, int64(startLocations[i]), s, 0)
}
// Final entry of table is just end pc.
setAddr(sb, ctxt.Arch, int64(funcIndex)*2*int64(ctxt.Arch.PtrSize), prevFunc, ldr.SymSize(prevFunc))
}
// writeFuncData writes the funcdata tables.
//
// This function executes a callback for each funcdata needed in
// runtime.functab. It should be called once for internally linked static
// binaries, or twice (once to generate the needed relocations) for other
// build modes.
//
// Note the output of this function is interwoven with writeFuncs, but this is
// a separate function, because it's needed in different passes in
// generateFunctab.
func (state *pclntab) writeFuncData(ctxt *Link, sb *loader.SymbolBuilder, funcs []loader.Sym, inlSyms map[loader.Sym]loader.Sym, startLocations []uint32, setAddr pclnSetAddr, setUint pclnSetUint) {
ldr := ctxt.loader
funcdata, funcdataoff := []loader.Sym{}, []int64{}
for i, s := range funcs {
fi := ldr.FuncInfo(s)
if !fi.Valid() {
continue
}
fi.Preload()
// funcdata, must be pointer-aligned and we're only int32-aligned.
// Missing funcdata will be 0 (nil pointer).
funcdata, funcdataoff := funcData(fi, inlSyms[s], funcdata, funcdataoff)
if len(funcdata) > 0 {
off := int64(startLocations[i] + state.funcSize + numPCData(fi)*4)
off = Rnd(off, int64(ctxt.Arch.PtrSize))
for j := range funcdata {
dataoff := off + int64(ctxt.Arch.PtrSize*j)
if funcdata[j] == 0 {
setUint(sb, ctxt.Arch, dataoff, uint64(funcdataoff[j]))
continue
}
// TODO: Does this need deduping?
setAddr(sb, ctxt.Arch, dataoff, funcdata[j], funcdataoff[j])
}
}
}
}
// writeFuncs writes the func structures and pcdata to runtime.functab.
func writeFuncs(ctxt *Link, sb *loader.SymbolBuilder, funcs []loader.Sym, inlSyms map[loader.Sym]loader.Sym, startLocations, cuOffsets []uint32, nameOffsets map[loader.Sym]uint32) {
ldr := ctxt.loader
deferReturnSym := ldr.Lookup("runtime.deferreturn", sym.SymVerABIInternal)
funcdata, funcdataoff := []loader.Sym{}, []int64{}
// Write the individual func objects.
for i, s := range funcs {
fi := ldr.FuncInfo(s)
if fi.Valid() {
fi.Preload()
}
// Note we skip the space for the entry value -- that's handled inn
// walkPCToFunc. We don't write it here, because it might require a
// relocation.
off := startLocations[i] + uint32(ctxt.Arch.PtrSize) // entry
// name int32
nameoff, ok := nameOffsets[s]
if !ok {
panic("couldn't find function name offset")
}
off = uint32(sb.SetUint32(ctxt.Arch, int64(off), uint32(nameoff)))
// args int32
// TODO: Move into funcinfo.
args := uint32(0)
if fi.Valid() {
args = uint32(fi.Args())
}
off = uint32(sb.SetUint32(ctxt.Arch, int64(off), args))
// deferreturn
deferreturn := computeDeferReturn(ctxt, deferReturnSym, s)
off = uint32(sb.SetUint32(ctxt.Arch, int64(off), deferreturn))
// pcdata
if fi.Valid() {
off = uint32(sb.SetUint32(ctxt.Arch, int64(off), uint32(ldr.SymValue(fi.Pcsp()))))
off = uint32(sb.SetUint32(ctxt.Arch, int64(off), uint32(ldr.SymValue(fi.Pcfile()))))
off = uint32(sb.SetUint32(ctxt.Arch, int64(off), uint32(ldr.SymValue(fi.Pcline()))))
} else {
off += 12
}
off = uint32(sb.SetUint32(ctxt.Arch, int64(off), uint32(numPCData(fi))))
// Store the offset to compilation unit's file table.
cuIdx := ^uint32(0)
if cu := ldr.SymUnit(s); cu != nil {
cuIdx = cuOffsets[cu.PclnIndex]
}
off = uint32(sb.SetUint32(ctxt.Arch, int64(off), cuIdx))
// funcID uint8
var funcID objabi.FuncID
if fi.Valid() {
funcID = fi.FuncID()
}
off = uint32(sb.SetUint8(ctxt.Arch, int64(off), uint8(funcID)))
// flag uint8
var flag objabi.FuncFlag
if fi.Valid() {
flag = fi.FuncFlag()
}
off = uint32(sb.SetUint8(ctxt.Arch, int64(off), uint8(flag)))
off += 1 // pad
// nfuncdata must be the final entry.
funcdata, funcdataoff = funcData(fi, 0, funcdata, funcdataoff)
off = uint32(sb.SetUint8(ctxt.Arch, int64(off), uint8(len(funcdata))))
// Output the pcdata.
if fi.Valid() {
for j, pcSym := range fi.Pcdata() {
sb.SetUint32(ctxt.Arch, int64(off+uint32(j*4)), uint32(ldr.SymValue(pcSym)))
}
if fi.NumInlTree() > 0 {
sb.SetUint32(ctxt.Arch, int64(off+objabi.PCDATA_InlTreeIndex*4), uint32(ldr.SymValue(fi.Pcinline())))
}
}
}
}
// pclntab initializes the pclntab symbol with
// runtime function and file name information.
// pclntab generates the pcln table for the link output.
func (ctxt *Link) pclntab(container loader.Bitmap) *pclntab {
// Go 1.2's symtab layout is documented in golang.org/s/go12symtab, but the
// layout and data has changed since that time.
//
// As of August 2020, here's the layout of pclntab:
//
// .gopclntab/__gopclntab [elf/macho section]
// runtime.pclntab
// Carrier symbol for the entire pclntab section.
//
// runtime.pcheader (see: runtime/symtab.go:pcHeader)
// 8-byte magic
// nfunc [thearch.ptrsize bytes]
// offset to runtime.funcnametab from the beginning of runtime.pcheader
// offset to runtime.pclntab_old from beginning of runtime.pcheader
//
// runtime.funcnametab
// []list of null terminated function names
//
// runtime.cutab
// for i=0..#CUs
// for j=0..#max used file index in CU[i]
// uint32 offset into runtime.filetab for the filename[j]
//
// runtime.filetab
// []null terminated filename strings
//
// runtime.pctab
// []byte of deduplicated pc data.
//
// runtime.functab
// function table, alternating PC and offset to func struct [each entry thearch.ptrsize bytes]
// end PC [thearch.ptrsize bytes]
// func structures, pcdata offsets, func data.
state, compUnits, funcs := makePclntab(ctxt, container)
ldr := ctxt.loader
state.carrier = ldr.LookupOrCreateSym("runtime.pclntab", 0)
ldr.MakeSymbolUpdater(state.carrier).SetType(sym.SPCLNTAB)
ldr.SetAttrReachable(state.carrier, true)
setCarrierSym(sym.SPCLNTAB, state.carrier)
state.generatePCHeader(ctxt)
nameOffsets := state.generateFuncnametab(ctxt, funcs)
cuOffsets := state.generateFilenameTabs(ctxt, compUnits, funcs)
state.generatePctab(ctxt, funcs)
inlSyms := makeInlSyms(ctxt, funcs, nameOffsets)
state.generateFunctab(ctxt, funcs, inlSyms, cuOffsets, nameOffsets)
return state
}
func gorootFinal() string {
root := buildcfg.GOROOT
if final := os.Getenv("GOROOT_FINAL"); final != "" {
root = final
}
return root
}
func expandGoroot(s string) string {
const n = len("$GOROOT")
if len(s) >= n+1 && s[:n] == "$GOROOT" && (s[n] == '/' || s[n] == '\\') {
return filepath.ToSlash(filepath.Join(gorootFinal(), s[n:]))
}
return s
}
const (
BUCKETSIZE = 256 * MINFUNC
SUBBUCKETS = 16
SUBBUCKETSIZE = BUCKETSIZE / SUBBUCKETS
NOIDX = 0x7fffffff
)
// findfunctab generates a lookup table to quickly find the containing
// function for a pc. See src/runtime/symtab.go:findfunc for details.
func (ctxt *Link) findfunctab(state *pclntab, container loader.Bitmap) {
ldr := ctxt.loader
// find min and max address
min := ldr.SymValue(ctxt.Textp[0])
lastp := ctxt.Textp[len(ctxt.Textp)-1]
max := ldr.SymValue(lastp) + ldr.SymSize(lastp)
// for each subbucket, compute the minimum of all symbol indexes
// that map to that subbucket.
n := int32((max - min + SUBBUCKETSIZE - 1) / SUBBUCKETSIZE)
nbuckets := int32((max - min + BUCKETSIZE - 1) / BUCKETSIZE)
size := 4*int64(nbuckets) + int64(n)
writeFindFuncTab := func(_ *Link, s loader.Sym) {
t := ldr.MakeSymbolUpdater(s)
indexes := make([]int32, n)
for i := int32(0); i < n; i++ {
indexes[i] = NOIDX
}
idx := int32(0)
for i, s := range ctxt.Textp {
if !emitPcln(ctxt, s, container) {
continue
}
p := ldr.SymValue(s)
var e loader.Sym
i++
if i < len(ctxt.Textp) {
e = ctxt.Textp[i]
}
for e != 0 && !emitPcln(ctxt, e, container) && i < len(ctxt.Textp) {
e = ctxt.Textp[i]
i++
}
q := max
if e != 0 {
q = ldr.SymValue(e)
}
//print("%d: [%lld %lld] %s\n", idx, p, q, s->name);
for ; p < q; p += SUBBUCKETSIZE {
i = int((p - min) / SUBBUCKETSIZE)
if indexes[i] > idx {
indexes[i] = idx
}
}
i = int((q - 1 - min) / SUBBUCKETSIZE)
if indexes[i] > idx {
indexes[i] = idx
}
idx++
}
// fill in table
for i := int32(0); i < nbuckets; i++ {
base := indexes[i*SUBBUCKETS]
if base == NOIDX {
Errorf(nil, "hole in findfunctab")
}
t.SetUint32(ctxt.Arch, int64(i)*(4+SUBBUCKETS), uint32(base))
for j := int32(0); j < SUBBUCKETS && i*SUBBUCKETS+j < n; j++ {
idx = indexes[i*SUBBUCKETS+j]
if idx == NOIDX {
Errorf(nil, "hole in findfunctab")
}
if idx-base >= 256 {
Errorf(nil, "too many functions in a findfunc bucket! %d/%d %d %d", i, nbuckets, j, idx-base)
}
t.SetUint8(ctxt.Arch, int64(i)*(4+SUBBUCKETS)+4+int64(j), uint8(idx-base))
}
}
}
state.findfunctab = ctxt.createGeneratorSymbol("runtime.findfunctab", 0, sym.SRODATA, size, writeFindFuncTab)
ldr.SetAttrReachable(state.findfunctab, true)
ldr.SetAttrLocal(state.findfunctab, true)
}
// findContainerSyms returns a bitmap, indexed by symbol number, where there's
// a 1 for every container symbol.
func (ctxt *Link) findContainerSyms() loader.Bitmap {
ldr := ctxt.loader
container := loader.MakeBitmap(ldr.NSym())
// Find container symbols and mark them as such.
for _, s := range ctxt.Textp {
outer := ldr.OuterSym(s)
if outer != 0 {
container.Set(outer)
}
}
return container
}
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