| // 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/objabi" |
| "cmd/internal/sys" |
| "cmd/link/internal/loader" |
| "cmd/link/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 deadcodePass struct { |
| ctxt *Link |
| ldr *loader.Loader |
| wq workQueue |
| |
| ifaceMethod map[methodsig]bool // methods declared in reached interfaces |
| markableMethods []methodref // methods of reached types |
| reflectSeen bool // whether we have seen a reflect method call |
| } |
| |
| func (d *deadcodePass) init() { |
| d.ldr.InitReachable() |
| d.ifaceMethod = make(map[methodsig]bool) |
| if objabi.Fieldtrack_enabled != 0 { |
| 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) |
| 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 { |
| relocs := d.ldr.Relocs(exportsIdx) |
| for i := 0; i < relocs.Count(); i++ { |
| d.mark(relocs.At2(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) |
| } |
| |
| 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 *deadcodePass) flood() { |
| for !d.wq.empty() { |
| symIdx := d.wq.pop() |
| |
| d.reflectSeen = d.reflectSeen || d.ldr.IsReflectMethod(symIdx) |
| |
| isgotype := d.ldr.IsGoType(symIdx) |
| relocs := d.ldr.Relocs(symIdx) |
| |
| if isgotype { |
| p := d.ldr.Data(symIdx) |
| if len(p) != 0 && decodetypeKind(d.ctxt.Arch, p)&kindMask == kindInterface { |
| for _, sig := range d.decodeIfaceMethods(d.ldr, d.ctxt.Arch, symIdx, &relocs) { |
| if d.ctxt.Debugvlog > 1 { |
| d.ctxt.Logf("reached iface method: %s\n", sig) |
| } |
| d.ifaceMethod[sig] = true |
| } |
| } |
| } |
| |
| var methods []methodref |
| for i := 0; i < relocs.Count(); i++ { |
| r := relocs.At2(i) |
| t := r.Type() |
| if t == objabi.R_WEAKADDROFF { |
| continue |
| } |
| if t == objabi.R_METHODOFF { |
| if i+2 >= relocs.Count() { |
| panic("expect three consecutive R_METHODOFF relocs") |
| } |
| methods = append(methods, methodref{src: symIdx, r: i}) |
| i += 2 |
| continue |
| } |
| if t == 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) |
| } |
| naux := d.ldr.NAux(symIdx) |
| for i := 0; i < naux; i++ { |
| d.mark(d.ldr.Aux2(symIdx, i).Sym(), 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. |
| if d.ldr.IsExternal(symIdx) { |
| d.mark(d.ldr.OuterSym(symIdx), symIdx) |
| d.mark(d.ldr.SubSym(symIdx), symIdx) |
| } |
| |
| if len(methods) != 0 { |
| if !isgotype { |
| panic("method found on non-type symbol") |
| } |
| // Decode runtime type information for type methods |
| // to help work out which methods can be called |
| // dynamically via interfaces. |
| methodsigs := d.decodetypeMethods(d.ldr, d.ctxt.Arch, symIdx, &relocs) |
| 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 *deadcodePass) mark(symIdx, parent loader.Sym) { |
| if symIdx != 0 && !d.ldr.AttrReachable(symIdx) { |
| d.wq.push(symIdx) |
| d.ldr.SetAttrReachable(symIdx, true) |
| if objabi.Fieldtrack_enabled != 0 { |
| 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 *deadcodePass) markMethod(m methodref) { |
| relocs := d.ldr.Relocs(m.src) |
| d.mark(relocs.At2(m.r).Sym(), m.src) |
| d.mark(relocs.At2(m.r+1).Sym(), m.src) |
| d.mark(relocs.At2(m.r+2).Sym(), m.src) |
| } |
| |
| // deadcode marks all reachable symbols. |
| // |
| // The basis of the dead code elimination is a flood fill of symbols, |
| // following their relocations, beginning at *flagEntrySymbol. |
| // |
| // This flood fill is wrapped in logic for pruning unused methods. |
| // All methods are mentioned by relocations on their receiver's *rtype. |
| // These relocations are specially defined as R_METHODOFF by the compiler |
| // so we can detect and manipulated them here. |
| // |
| // There are three ways a method of a reachable type can be invoked: |
| // |
| // 1. direct call |
| // 2. through a reachable interface type |
| // 3. reflect.Value.Method (or MethodByName), or reflect.Type.Method |
| // (or MethodByName) |
| // |
| // The first case is handled by the flood fill, a directly called method |
| // is marked as reachable. |
| // |
| // The second case is handled by decomposing all reachable interface |
| // types into method signatures. Each encountered method is compared |
| // against the interface method signatures, if it matches it is marked |
| // as reachable. This is extremely conservative, but easy and correct. |
| // |
| // The third case is handled by looking to see if any of: |
| // - reflect.Value.Method or MethodByName is reachable |
| // - reflect.Type.Method or MethodByName is called (through the |
| // REFLECTMETHOD attribute marked by the compiler). |
| // If any of these happen, all bets are off and all exported methods |
| // of reachable types are marked reachable. |
| // |
| // Any unreached text symbols are removed from ctxt.Textp. |
| func deadcode(ctxt *Link) { |
| ldr := ctxt.loader |
| d := deadcodePass{ctxt: ctxt, ldr: ldr} |
| d.init() |
| d.flood() |
| |
| methSym := ldr.Lookup("reflect.Value.Method", sym.SymVerABIInternal) |
| methByNameSym := ldr.Lookup("reflect.Value.MethodByName", 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 || (methSym != 0 && ldr.AttrReachable(methSym)) || (methByNameSym != 0 && ldr.AttrReachable(methByNameSym)) |
| |
| // 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.AttrReachable(relocs.At2(0).Sym()) { |
| ldr.SetAttrReachable(s, true) |
| } |
| } |
| } |
| } |
| } |
| |
| // methodref 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 methodref struct { |
| m methodsig |
| src loader.Sym // receiver type symbol |
| r int // the index of R_METHODOFF relocations |
| } |
| |
| func (m methodref) 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 *deadcodePass) decodeMethodSig(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, relocs *loader.Relocs, off, size, count int) []methodsig { |
| var buf bytes.Buffer |
| var methods []methodsig |
| for i := 0; i < count; i++ { |
| buf.WriteString(decodetypeName(ldr, symIdx, relocs, off)) |
| mtypSym := decodeRelocSym(ldr, symIdx, relocs, int32(off+4)) |
| // FIXME: add some sort of caching here, since we may see some of the |
| // same symbols over time for param types. |
| mrelocs := ldr.Relocs(mtypSym) |
| mp := ldr.Data(mtypSym) |
| |
| buf.WriteRune('(') |
| inCount := decodetypeFuncInCount(arch, mp) |
| for i := 0; i < inCount; i++ { |
| if i > 0 { |
| buf.WriteString(", ") |
| } |
| a := decodetypeFuncInType(ldr, arch, mtypSym, &mrelocs, i) |
| buf.WriteString(ldr.SymName(a)) |
| } |
| buf.WriteString(") (") |
| outCount := decodetypeFuncOutCount(arch, mp) |
| for i := 0; i < outCount; i++ { |
| if i > 0 { |
| buf.WriteString(", ") |
| } |
| a := decodetypeFuncOutType(ldr, arch, mtypSym, &mrelocs, i) |
| buf.WriteString(ldr.SymName(a)) |
| } |
| buf.WriteRune(')') |
| |
| off += size |
| methods = append(methods, methodsig(buf.String())) |
| buf.Reset() |
| } |
| return methods |
| } |
| |
| func (d *deadcodePass) decodeIfaceMethods(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, relocs *loader.Relocs) []methodsig { |
| p := ldr.Data(symIdx) |
| if decodetypeKind(arch, p)&kindMask != kindInterface { |
| panic(fmt.Sprintf("symbol %q is not an interface", ldr.SymName(symIdx))) |
| } |
| rel := decodeReloc(ldr, symIdx, relocs, int32(commonsize(arch)+arch.PtrSize)) |
| s := rel.Sym() |
| if s == 0 { |
| return nil |
| } |
| if s != 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.decodeMethodSig(ldr, arch, symIdx, relocs, off, sizeofIMethod, numMethods) |
| } |
| |
| func (d *deadcodePass) decodetypeMethods(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, relocs *loader.Relocs) []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.decodeMethodSig(ldr, arch, symIdx, relocs, off, sizeofMethod, mcount) |
| } |
