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path: root/src/cmd/oldlink/internal/ld/deadcode2.go
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Diffstat (limited to 'src/cmd/oldlink/internal/ld/deadcode2.go')
-rw-r--r--src/cmd/oldlink/internal/ld/deadcode2.go441
1 files changed, 441 insertions, 0 deletions
diff --git a/src/cmd/oldlink/internal/ld/deadcode2.go b/src/cmd/oldlink/internal/ld/deadcode2.go
new file mode 100644
index 0000000000..82bfd60a47
--- /dev/null
+++ b/src/cmd/oldlink/internal/ld/deadcode2.go
@@ -0,0 +1,441 @@
+// Copyright 2019 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/dwarf"
+ "cmd/internal/objabi"
+ "cmd/internal/sys"
+ "cmd/oldlink/internal/loader"
+ "cmd/oldlink/internal/sym"
+ "container/heap"
+ "fmt"
+ "unicode"
+)
+
+var _ = fmt.Print
+
+type workQueue []loader.Sym
+
+// Implement container/heap.Interface.
+func (q *workQueue) Len() int { return len(*q) }
+func (q *workQueue) Less(i, j int) bool { return (*q)[i] < (*q)[j] }
+func (q *workQueue) Swap(i, j int) { (*q)[i], (*q)[j] = (*q)[j], (*q)[i] }
+func (q *workQueue) Push(i interface{}) { *q = append(*q, i.(loader.Sym)) }
+func (q *workQueue) Pop() interface{} { i := (*q)[len(*q)-1]; *q = (*q)[:len(*q)-1]; return i }
+
+// Functions for deadcode pass to use.
+// Deadcode pass should call push/pop, not Push/Pop.
+func (q *workQueue) push(i loader.Sym) { heap.Push(q, i) }
+func (q *workQueue) pop() loader.Sym { return heap.Pop(q).(loader.Sym) }
+func (q *workQueue) empty() bool { return len(*q) == 0 }
+
+type deadcodePass2 struct {
+ ctxt *Link
+ ldr *loader.Loader
+ wq workQueue
+ rtmp []loader.Reloc
+
+ ifaceMethod map[methodsig]bool // methods declared in reached interfaces
+ markableMethods []methodref2 // methods of reached types
+ reflectSeen bool // whether we have seen a reflect method call
+}
+
+func (d *deadcodePass2) init() {
+ d.ldr.InitReachable()
+ d.ifaceMethod = make(map[methodsig]bool)
+ if d.ctxt.Reachparent != nil {
+ d.ldr.Reachparent = make([]loader.Sym, d.ldr.NSym())
+ }
+ heap.Init(&d.wq)
+
+ if d.ctxt.BuildMode == BuildModeShared {
+ // Mark all symbols defined in this library as reachable when
+ // building a shared library.
+ n := d.ldr.NDef()
+ for i := 1; i < n; i++ {
+ s := loader.Sym(i)
+ if !d.ldr.IsDup(s) {
+ d.mark(s, 0)
+ }
+ }
+ return
+ }
+
+ var names []string
+
+ // In a normal binary, start at main.main and the init
+ // functions and mark what is reachable from there.
+ if d.ctxt.linkShared && (d.ctxt.BuildMode == BuildModeExe || d.ctxt.BuildMode == BuildModePIE) {
+ names = append(names, "main.main", "main..inittask")
+ } else {
+ // The external linker refers main symbol directly.
+ if d.ctxt.LinkMode == LinkExternal && (d.ctxt.BuildMode == BuildModeExe || d.ctxt.BuildMode == BuildModePIE) {
+ if d.ctxt.HeadType == objabi.Hwindows && d.ctxt.Arch.Family == sys.I386 {
+ *flagEntrySymbol = "_main"
+ } else {
+ *flagEntrySymbol = "main"
+ }
+ }
+ names = append(names, *flagEntrySymbol)
+ if d.ctxt.BuildMode == BuildModePlugin {
+ names = append(names, objabi.PathToPrefix(*flagPluginPath)+"..inittask", objabi.PathToPrefix(*flagPluginPath)+".main", "go.plugin.tabs")
+
+ // We don't keep the go.plugin.exports symbol,
+ // but we do keep the symbols it refers to.
+ exportsIdx := d.ldr.Lookup("go.plugin.exports", 0)
+ if exportsIdx != 0 {
+ d.ReadRelocs(exportsIdx)
+ for i := 0; i < len(d.rtmp); i++ {
+ d.mark(d.rtmp[i].Sym, 0)
+ }
+ }
+ }
+ }
+
+ dynexpMap := d.ctxt.cgo_export_dynamic
+ if d.ctxt.LinkMode == LinkExternal {
+ dynexpMap = d.ctxt.cgo_export_static
+ }
+ for exp := range dynexpMap {
+ names = append(names, exp)
+ }
+
+ // DWARF constant DIE symbols are not referenced, but needed by
+ // the dwarf pass.
+ if !*FlagW {
+ for _, lib := range d.ctxt.Library {
+ names = append(names, dwarf.ConstInfoPrefix+lib.Pkg)
+ }
+ }
+
+ for _, name := range names {
+ // Mark symbol as a data/ABI0 symbol.
+ d.mark(d.ldr.Lookup(name, 0), 0)
+ // Also mark any Go functions (internal ABI).
+ d.mark(d.ldr.Lookup(name, sym.SymVerABIInternal), 0)
+ }
+}
+
+func (d *deadcodePass2) flood() {
+ symRelocs := []loader.Reloc{}
+ auxSyms := []loader.Sym{}
+ for !d.wq.empty() {
+ symIdx := d.wq.pop()
+
+ d.reflectSeen = d.reflectSeen || d.ldr.IsReflectMethod(symIdx)
+
+ relocs := d.ldr.Relocs(symIdx)
+ symRelocs = relocs.ReadAll(symRelocs)
+
+ if d.ldr.IsGoType(symIdx) {
+ p := d.ldr.Data(symIdx)
+ if len(p) != 0 && decodetypeKind(d.ctxt.Arch, p)&kindMask == kindInterface {
+ for _, sig := range d.decodeIfaceMethods2(d.ldr, d.ctxt.Arch, symIdx, symRelocs) {
+ if d.ctxt.Debugvlog > 1 {
+ d.ctxt.Logf("reached iface method: %s\n", sig)
+ }
+ d.ifaceMethod[sig] = true
+ }
+ }
+ }
+
+ var methods []methodref2
+ for i := 0; i < relocs.Count; i++ {
+ r := symRelocs[i]
+ if r.Type == objabi.R_WEAKADDROFF {
+ continue
+ }
+ if r.Type == objabi.R_METHODOFF {
+ if i+2 >= relocs.Count {
+ panic("expect three consecutive R_METHODOFF relocs")
+ }
+ methods = append(methods, methodref2{src: symIdx, r: i})
+ i += 2
+ continue
+ }
+ if r.Type == objabi.R_USETYPE {
+ // type symbol used for DWARF. we need to load the symbol but it may not
+ // be otherwise reachable in the program.
+ // do nothing for now as we still load all type symbols.
+ continue
+ }
+ d.mark(r.Sym, symIdx)
+ }
+ auxSyms = d.ldr.ReadAuxSyms(symIdx, auxSyms)
+ for i := 0; i < len(auxSyms); i++ {
+ d.mark(auxSyms[i], symIdx)
+ }
+ // Some host object symbols have an outer object, which acts like a
+ // "carrier" symbol, or it holds all the symbols for a particular
+ // section. We need to mark all "referenced" symbols from that carrier,
+ // so we make sure we're pulling in all outer symbols, and their sub
+ // symbols. This is not ideal, and these carrier/section symbols could
+ // be removed.
+ d.mark(d.ldr.OuterSym(symIdx), symIdx)
+ d.mark(d.ldr.SubSym(symIdx), symIdx)
+
+ if len(methods) != 0 {
+ // Decode runtime type information for type methods
+ // to help work out which methods can be called
+ // dynamically via interfaces.
+ methodsigs := d.decodetypeMethods2(d.ldr, d.ctxt.Arch, symIdx, symRelocs)
+ if len(methods) != len(methodsigs) {
+ panic(fmt.Sprintf("%q has %d method relocations for %d methods", d.ldr.SymName(symIdx), len(methods), len(methodsigs)))
+ }
+ for i, m := range methodsigs {
+ methods[i].m = m
+ }
+ d.markableMethods = append(d.markableMethods, methods...)
+ }
+ }
+}
+
+func (d *deadcodePass2) mark(symIdx, parent loader.Sym) {
+ if symIdx != 0 && !d.ldr.Reachable.Has(symIdx) {
+ d.wq.push(symIdx)
+ d.ldr.Reachable.Set(symIdx)
+ if d.ctxt.Reachparent != nil {
+ d.ldr.Reachparent[symIdx] = parent
+ }
+ if *flagDumpDep {
+ to := d.ldr.SymName(symIdx)
+ if to != "" {
+ from := "_"
+ if parent != 0 {
+ from = d.ldr.SymName(parent)
+ }
+ fmt.Printf("%s -> %s\n", from, to)
+ }
+ }
+ }
+}
+
+func (d *deadcodePass2) markMethod(m methodref2) {
+ d.ReadRelocs(m.src)
+ d.mark(d.rtmp[m.r].Sym, m.src)
+ d.mark(d.rtmp[m.r+1].Sym, m.src)
+ d.mark(d.rtmp[m.r+2].Sym, m.src)
+}
+
+func deadcode2(ctxt *Link) {
+ ldr := ctxt.loader
+ d := deadcodePass2{ctxt: ctxt, ldr: ldr}
+ d.init()
+ d.flood()
+
+ callSym := ldr.Lookup("reflect.Value.Call", sym.SymVerABIInternal)
+ methSym := ldr.Lookup("reflect.Value.Method", sym.SymVerABIInternal)
+ if ctxt.DynlinkingGo() {
+ // Exported methods may satisfy interfaces we don't know
+ // about yet when dynamically linking.
+ d.reflectSeen = true
+ }
+
+ for {
+ // Methods might be called via reflection. Give up on
+ // static analysis, mark all exported methods of
+ // all reachable types as reachable.
+ d.reflectSeen = d.reflectSeen || (callSym != 0 && ldr.Reachable.Has(callSym)) || (methSym != 0 && ldr.Reachable.Has(methSym))
+
+ // Mark all methods that could satisfy a discovered
+ // interface as reachable. We recheck old marked interfaces
+ // as new types (with new methods) may have been discovered
+ // in the last pass.
+ rem := d.markableMethods[:0]
+ for _, m := range d.markableMethods {
+ if (d.reflectSeen && m.isExported()) || d.ifaceMethod[m.m] {
+ d.markMethod(m)
+ } else {
+ rem = append(rem, m)
+ }
+ }
+ d.markableMethods = rem
+
+ if d.wq.empty() {
+ // No new work was discovered. Done.
+ break
+ }
+ d.flood()
+ }
+
+ n := ldr.NSym()
+
+ if ctxt.BuildMode != BuildModeShared {
+ // Keep a itablink if the symbol it points at is being kept.
+ // (When BuildModeShared, always keep itablinks.)
+ for i := 1; i < n; i++ {
+ s := loader.Sym(i)
+ if ldr.IsItabLink(s) {
+ relocs := ldr.Relocs(s)
+ if relocs.Count > 0 && ldr.Reachable.Has(relocs.At(0).Sym) {
+ ldr.Reachable.Set(s)
+ }
+ }
+ }
+ }
+}
+
+// methodref2 holds the relocations from a receiver type symbol to its
+// method. There are three relocations, one for each of the fields in
+// the reflect.method struct: mtyp, ifn, and tfn.
+type methodref2 struct {
+ m methodsig
+ src loader.Sym // receiver type symbol
+ r int // the index of R_METHODOFF relocations
+}
+
+func (m methodref2) isExported() bool {
+ for _, r := range m.m {
+ return unicode.IsUpper(r)
+ }
+ panic("methodref has no signature")
+}
+
+// decodeMethodSig2 decodes an array of method signature information.
+// Each element of the array is size bytes. The first 4 bytes is a
+// nameOff for the method name, and the next 4 bytes is a typeOff for
+// the function type.
+//
+// Conveniently this is the layout of both runtime.method and runtime.imethod.
+func (d *deadcodePass2) decodeMethodSig2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc, off, size, count int) []methodsig {
+ var buf bytes.Buffer
+ var methods []methodsig
+ for i := 0; i < count; i++ {
+ buf.WriteString(decodetypeName2(ldr, symIdx, symRelocs, off))
+ mtypSym := decodeRelocSym2(ldr, symIdx, symRelocs, int32(off+4))
+ // FIXME: add some sort of caching here, since we may see some of the
+ // same symbols over time for param types.
+ d.ReadRelocs(mtypSym)
+ mp := ldr.Data(mtypSym)
+
+ buf.WriteRune('(')
+ inCount := decodetypeFuncInCount(arch, mp)
+ for i := 0; i < inCount; i++ {
+ if i > 0 {
+ buf.WriteString(", ")
+ }
+ a := d.decodetypeFuncInType2(ldr, arch, mtypSym, d.rtmp, i)
+ buf.WriteString(ldr.SymName(a))
+ }
+ buf.WriteString(") (")
+ outCount := decodetypeFuncOutCount(arch, mp)
+ for i := 0; i < outCount; i++ {
+ if i > 0 {
+ buf.WriteString(", ")
+ }
+ a := d.decodetypeFuncOutType2(ldr, arch, mtypSym, d.rtmp, i)
+ buf.WriteString(ldr.SymName(a))
+ }
+ buf.WriteRune(')')
+
+ off += size
+ methods = append(methods, methodsig(buf.String()))
+ buf.Reset()
+ }
+ return methods
+}
+
+func (d *deadcodePass2) decodeIfaceMethods2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc) []methodsig {
+ p := ldr.Data(symIdx)
+ if decodetypeKind(arch, p)&kindMask != kindInterface {
+ panic(fmt.Sprintf("symbol %q is not an interface", ldr.SymName(symIdx)))
+ }
+ rel := decodeReloc2(ldr, symIdx, symRelocs, int32(commonsize(arch)+arch.PtrSize))
+ if rel.Sym == 0 {
+ return nil
+ }
+ if rel.Sym != symIdx {
+ panic(fmt.Sprintf("imethod slice pointer in %q leads to a different symbol", ldr.SymName(symIdx)))
+ }
+ off := int(rel.Add) // array of reflect.imethod values
+ numMethods := int(decodetypeIfaceMethodCount(arch, p))
+ sizeofIMethod := 4 + 4
+ return d.decodeMethodSig2(ldr, arch, symIdx, symRelocs, off, sizeofIMethod, numMethods)
+}
+
+func (d *deadcodePass2) decodetypeMethods2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc) []methodsig {
+ p := ldr.Data(symIdx)
+ if !decodetypeHasUncommon(arch, p) {
+ panic(fmt.Sprintf("no methods on %q", ldr.SymName(symIdx)))
+ }
+ off := commonsize(arch) // reflect.rtype
+ switch decodetypeKind(arch, p) & kindMask {
+ case kindStruct: // reflect.structType
+ off += 4 * arch.PtrSize
+ case kindPtr: // reflect.ptrType
+ off += arch.PtrSize
+ case kindFunc: // reflect.funcType
+ off += arch.PtrSize // 4 bytes, pointer aligned
+ case kindSlice: // reflect.sliceType
+ off += arch.PtrSize
+ case kindArray: // reflect.arrayType
+ off += 3 * arch.PtrSize
+ case kindChan: // reflect.chanType
+ off += 2 * arch.PtrSize
+ case kindMap: // reflect.mapType
+ off += 4*arch.PtrSize + 8
+ case kindInterface: // reflect.interfaceType
+ off += 3 * arch.PtrSize
+ default:
+ // just Sizeof(rtype)
+ }
+
+ mcount := int(decodeInuxi(arch, p[off+4:], 2))
+ moff := int(decodeInuxi(arch, p[off+4+2+2:], 4))
+ off += moff // offset to array of reflect.method values
+ const sizeofMethod = 4 * 4 // sizeof reflect.method in program
+ return d.decodeMethodSig2(ldr, arch, symIdx, symRelocs, off, sizeofMethod, mcount)
+}
+
+func decodeReloc2(ldr *loader.Loader, symIdx loader.Sym, symRelocs []loader.Reloc, off int32) loader.Reloc {
+ for j := 0; j < len(symRelocs); j++ {
+ rel := symRelocs[j]
+ if rel.Off == off {
+ return rel
+ }
+ }
+ return loader.Reloc{}
+}
+
+func decodeRelocSym2(ldr *loader.Loader, symIdx loader.Sym, symRelocs []loader.Reloc, off int32) loader.Sym {
+ return decodeReloc2(ldr, symIdx, symRelocs, off).Sym
+}
+
+// decodetypeName2 decodes the name from a reflect.name.
+func decodetypeName2(ldr *loader.Loader, symIdx loader.Sym, symRelocs []loader.Reloc, off int) string {
+ r := decodeRelocSym2(ldr, symIdx, symRelocs, int32(off))
+ if r == 0 {
+ return ""
+ }
+
+ data := ldr.Data(r)
+ namelen := int(uint16(data[1])<<8 | uint16(data[2]))
+ return string(data[3 : 3+namelen])
+}
+
+func (d *deadcodePass2) decodetypeFuncInType2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc, i int) loader.Sym {
+ uadd := commonsize(arch) + 4
+ if arch.PtrSize == 8 {
+ uadd += 4
+ }
+ if decodetypeHasUncommon(arch, ldr.Data(symIdx)) {
+ uadd += uncommonSize()
+ }
+ return decodeRelocSym2(ldr, symIdx, symRelocs, int32(uadd+i*arch.PtrSize))
+}
+
+func (d *deadcodePass2) decodetypeFuncOutType2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc, i int) loader.Sym {
+ return d.decodetypeFuncInType2(ldr, arch, symIdx, symRelocs, i+decodetypeFuncInCount(arch, ldr.Data(symIdx)))
+}
+
+// readRelocs reads the relocations for the specified symbol into the
+// deadcode relocs work array. Use with care, since the work array
+// is a singleton.
+func (d *deadcodePass2) ReadRelocs(symIdx loader.Sym) {
+ relocs := d.ldr.Relocs(symIdx)
+ d.rtmp = relocs.ReadAll(d.rtmp)
+}
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