1 files changed, 412 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/gc/dwarf.go b/src/cmd/compile/internal/gc/dwarf.go
new file mode 100644
index 0000000000..e853c51422
--- /dev/null
+++ b/src/cmd/compile/internal/gc/dwarf.go
@@ -0,0 +1,412 @@
+// Copyright 2011 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 gc
+
+import (
+	"sort"
+
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/ssa"
+	"cmd/compile/internal/ssagen"
+	"cmd/compile/internal/types"
+	"cmd/internal/dwarf"
+	"cmd/internal/obj"
+	"cmd/internal/objabi"
+	"cmd/internal/src"
+)
+
+func debuginfo(fnsym *obj.LSym, infosym *obj.LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls) {
+	fn := curfn.(*ir.Func)
+
+	if fn.Nname != nil {
+		expect := fn.Sym().Linksym()
+		if fnsym.ABI() == obj.ABI0 {
+			expect = fn.Sym().LinksymABI0()
+		}
+		if fnsym != expect {
+			base.Fatalf("unexpected fnsym: %v != %v", fnsym, expect)
+		}
+	}
+
+	// Back when there were two different *Funcs for a function, this code
+	// was not consistent about whether a particular *Node being processed
+	// was an ODCLFUNC or ONAME node. Partly this is because inlined function
+	// bodies have no ODCLFUNC node, which was it's own inconsistency.
+	// In any event, the handling of the two different nodes for DWARF purposes
+	// was subtly different, likely in unintended ways. CL 272253 merged the
+	// two nodes' Func fields, so that code sees the same *Func whether it is
+	// holding the ODCLFUNC or the ONAME. This resulted in changes in the
+	// DWARF output. To preserve the existing DWARF output and leave an
+	// intentional change for a future CL, this code does the following when
+	// fn.Op == ONAME:
+	//
+	// 1. Disallow use of createComplexVars in createDwarfVars.
+	//    It was not possible to reach that code for an ONAME before,
+	//    because the DebugInfo was set only on the ODCLFUNC Func.
+	//    Calling into it in the ONAME case causes an index out of bounds panic.
+	//
+	// 2. Do not populate apdecls. fn.Func.Dcl was in the ODCLFUNC Func,
+	//    not the ONAME Func. Populating apdecls for the ONAME case results
+	//    in selected being populated after createSimpleVars is called in
+	//    createDwarfVars, and then that causes the loop to skip all the entries
+	//    in dcl, meaning that the RecordAutoType calls don't happen.
+	//
+	// These two adjustments keep toolstash -cmp working for now.
+	// Deciding the right answer is, as they say, future work.
+	//
+	// We can tell the difference between the old ODCLFUNC and ONAME
+	// cases by looking at the infosym.Name. If it's empty, DebugInfo is
+	// being called from (*obj.Link).populateDWARF, which used to use
+	// the ODCLFUNC. If it's non-empty (the name will end in $abstract),
+	// DebugInfo is being called from (*obj.Link).DwarfAbstractFunc,
+	// which used to use the ONAME form.
+	isODCLFUNC := infosym.Name == ""
+
+	var apdecls []*ir.Name
+	// Populate decls for fn.
+	if isODCLFUNC {
+		for _, n := range fn.Dcl {
+			if n.Op() != ir.ONAME { // might be OTYPE or OLITERAL
+				continue
+			}
+			switch n.Class_ {
+			case ir.PAUTO:
+				if !n.Used() {
+					// Text == nil -> generating abstract function
+					if fnsym.Func().Text != nil {
+						base.Fatalf("debuginfo unused node (AllocFrame should truncate fn.Func.Dcl)")
+					}
+					continue
+				}
+			case ir.PPARAM, ir.PPARAMOUT:
+			default:
+				continue
+			}
+			apdecls = append(apdecls, n)
+			fnsym.Func().RecordAutoType(ngotype(n).Linksym())
+		}
+	}
+
+	decls, dwarfVars := createDwarfVars(fnsym, isODCLFUNC, fn, apdecls)
+
+	// For each type referenced by the functions auto vars but not
+	// already referenced by a dwarf var, attach an R_USETYPE relocation to
+	// the function symbol to insure that the type included in DWARF
+	// processing during linking.
+	typesyms := []*obj.LSym{}
+	for t, _ := range fnsym.Func().Autot {
+		typesyms = append(typesyms, t)
+	}
+	sort.Sort(obj.BySymName(typesyms))
+	for _, sym := range typesyms {
+		r := obj.Addrel(infosym)
+		r.Sym = sym
+		r.Type = objabi.R_USETYPE
+	}
+	fnsym.Func().Autot = nil
+
+	var varScopes []ir.ScopeID
+	for _, decl := range decls {
+		pos := declPos(decl)
+		varScopes = append(varScopes, findScope(fn.Marks, pos))
+	}
+
+	scopes := assembleScopes(fnsym, fn, dwarfVars, varScopes)
+	var inlcalls dwarf.InlCalls
+	if base.Flag.GenDwarfInl > 0 {
+		inlcalls = assembleInlines(fnsym, dwarfVars)
+	}
+	return scopes, inlcalls
+}
+
+func declPos(decl *ir.Name) src.XPos {
+	if decl.Name().Defn != nil && (decl.Name().Captured() || decl.Name().Byval()) {
+		// It's not clear which position is correct for captured variables here:
+		// * decl.Pos is the wrong position for captured variables, in the inner
+		//   function, but it is the right position in the outer function.
+		// * decl.Name.Defn is nil for captured variables that were arguments
+		//   on the outer function, however the decl.Pos for those seems to be
+		//   correct.
+		// * decl.Name.Defn is the "wrong" thing for variables declared in the
+		//   header of a type switch, it's their position in the header, rather
+		//   than the position of the case statement. In principle this is the
+		//   right thing, but here we prefer the latter because it makes each
+		//   instance of the header variable local to the lexical block of its
+		//   case statement.
+		// This code is probably wrong for type switch variables that are also
+		// captured.
+		return decl.Name().Defn.Pos()
+	}
+	return decl.Pos()
+}
+
+// createDwarfVars process fn, returning a list of DWARF variables and the
+// Nodes they represent.
+func createDwarfVars(fnsym *obj.LSym, complexOK bool, fn *ir.Func, apDecls []*ir.Name) ([]*ir.Name, []*dwarf.Var) {
+	// Collect a raw list of DWARF vars.
+	var vars []*dwarf.Var
+	var decls []*ir.Name
+	var selected map[*ir.Name]bool
+	if base.Ctxt.Flag_locationlists && base.Ctxt.Flag_optimize && fn.DebugInfo != nil && complexOK {
+		decls, vars, selected = createComplexVars(fnsym, fn)
+	} else {
+		decls, vars, selected = createSimpleVars(fnsym, apDecls)
+	}
+
+	dcl := apDecls
+	if fnsym.WasInlined() {
+		dcl = preInliningDcls(fnsym)
+	}
+
+	// If optimization is enabled, the list above will typically be
+	// missing some of the original pre-optimization variables in the
+	// function (they may have been promoted to registers, folded into
+	// constants, dead-coded away, etc).  Input arguments not eligible
+	// for SSA optimization are also missing.  Here we add back in entries
+	// for selected missing vars. Note that the recipe below creates a
+	// conservative location. The idea here is that we want to
+	// communicate to the user that "yes, there is a variable named X
+	// in this function, but no, I don't have enough information to
+	// reliably report its contents."
+	// For non-SSA-able arguments, however, the correct information
+	// is known -- they have a single home on the stack.
+	for _, n := range dcl {
+		if _, found := selected[n]; found {
+			continue
+		}
+		c := n.Sym().Name[0]
+		if c == '.' || n.Type().IsUntyped() {
+			continue
+		}
+		if n.Class_ == ir.PPARAM && !ssagen.TypeOK(n.Type()) {
+			// SSA-able args get location lists, and may move in and
+			// out of registers, so those are handled elsewhere.
+			// Autos and named output params seem to get handled
+			// with VARDEF, which creates location lists.
+			// Args not of SSA-able type are treated here; they
+			// are homed on the stack in a single place for the
+			// entire call.
+			vars = append(vars, createSimpleVar(fnsym, n))
+			decls = append(decls, n)
+			continue
+		}
+		typename := dwarf.InfoPrefix + types.TypeSymName(n.Type())
+		decls = append(decls, n)
+		abbrev := dwarf.DW_ABRV_AUTO_LOCLIST
+		isReturnValue := (n.Class_ == ir.PPARAMOUT)
+		if n.Class_ == ir.PPARAM || n.Class_ == ir.PPARAMOUT {
+			abbrev = dwarf.DW_ABRV_PARAM_LOCLIST
+		} else if n.Class_ == ir.PAUTOHEAP {
+			// If dcl in question has been promoted to heap, do a bit
+			// of extra work to recover original class (auto or param);
+			// see issue 30908. This insures that we get the proper
+			// signature in the abstract function DIE, but leaves a
+			// misleading location for the param (we want pointer-to-heap
+			// and not stack).
+			// TODO(thanm): generate a better location expression
+			stackcopy := n.Name().Stackcopy
+			if stackcopy != nil && (stackcopy.Class_ == ir.PPARAM || stackcopy.Class_ == ir.PPARAMOUT) {
+				abbrev = dwarf.DW_ABRV_PARAM_LOCLIST
+				isReturnValue = (stackcopy.Class_ == ir.PPARAMOUT)
+			}
+		}
+		inlIndex := 0
+		if base.Flag.GenDwarfInl > 1 {
+			if n.Name().InlFormal() || n.Name().InlLocal() {
+				inlIndex = posInlIndex(n.Pos()) + 1
+				if n.Name().InlFormal() {
+					abbrev = dwarf.DW_ABRV_PARAM_LOCLIST
+				}
+			}
+		}
+		declpos := base.Ctxt.InnermostPos(n.Pos())
+		vars = append(vars, &dwarf.Var{
+			Name:          n.Sym().Name,
+			IsReturnValue: isReturnValue,
+			Abbrev:        abbrev,
+			StackOffset:   int32(n.FrameOffset()),
+			Type:          base.Ctxt.Lookup(typename),
+			DeclFile:      declpos.RelFilename(),
+			DeclLine:      declpos.RelLine(),
+			DeclCol:       declpos.Col(),
+			InlIndex:      int32(inlIndex),
+			ChildIndex:    -1,
+		})
+		// Record go type of to insure that it gets emitted by the linker.
+		fnsym.Func().RecordAutoType(ngotype(n).Linksym())
+	}
+
+	return decls, vars
+}
+
+// Given a function that was inlined at some point during the
+// compilation, return a sorted list of nodes corresponding to the
+// autos/locals in that function prior to inlining. If this is a
+// function that is not local to the package being compiled, then the
+// names of the variables may have been "versioned" to avoid conflicts
+// with local vars; disregard this versioning when sorting.
+func preInliningDcls(fnsym *obj.LSym) []*ir.Name {
+	fn := base.Ctxt.DwFixups.GetPrecursorFunc(fnsym).(*ir.Func)
+	var rdcl []*ir.Name
+	for _, n := range fn.Inl.Dcl {
+		c := n.Sym().Name[0]
+		// Avoid reporting "_" parameters, since if there are more than
+		// one, it can result in a collision later on, as in #23179.
+		if unversion(n.Sym().Name) == "_" || c == '.' || n.Type().IsUntyped() {
+			continue
+		}
+		rdcl = append(rdcl, n)
+	}
+	return rdcl
+}
+
+// createSimpleVars creates a DWARF entry for every variable declared in the
+// function, claiming that they are permanently on the stack.
+func createSimpleVars(fnsym *obj.LSym, apDecls []*ir.Name) ([]*ir.Name, []*dwarf.Var, map[*ir.Name]bool) {
+	var vars []*dwarf.Var
+	var decls []*ir.Name
+	selected := make(map[*ir.Name]bool)
+	for _, n := range apDecls {
+		if ir.IsAutoTmp(n) {
+			continue
+		}
+
+		decls = append(decls, n)
+		vars = append(vars, createSimpleVar(fnsym, n))
+		selected[n] = true
+	}
+	return decls, vars, selected
+}
+
+func createSimpleVar(fnsym *obj.LSym, n *ir.Name) *dwarf.Var {
+	var abbrev int
+	var offs int64
+
+	switch n.Class_ {
+	case ir.PAUTO:
+		offs = n.FrameOffset()
+		abbrev = dwarf.DW_ABRV_AUTO
+		if base.Ctxt.FixedFrameSize() == 0 {
+			offs -= int64(types.PtrSize)
+		}
+		if objabi.Framepointer_enabled || objabi.GOARCH == "arm64" {
+			// There is a word space for FP on ARM64 even if the frame pointer is disabled
+			offs -= int64(types.PtrSize)
+		}
+
+	case ir.PPARAM, ir.PPARAMOUT:
+		abbrev = dwarf.DW_ABRV_PARAM
+		offs = n.FrameOffset() + base.Ctxt.FixedFrameSize()
+	default:
+		base.Fatalf("createSimpleVar unexpected class %v for node %v", n.Class_, n)
+	}
+
+	typename := dwarf.InfoPrefix + types.TypeSymName(n.Type())
+	delete(fnsym.Func().Autot, ngotype(n).Linksym())
+	inlIndex := 0
+	if base.Flag.GenDwarfInl > 1 {
+		if n.Name().InlFormal() || n.Name().InlLocal() {
+			inlIndex = posInlIndex(n.Pos()) + 1
+			if n.Name().InlFormal() {
+				abbrev = dwarf.DW_ABRV_PARAM
+			}
+		}
+	}
+	declpos := base.Ctxt.InnermostPos(declPos(n))
+	return &dwarf.Var{
+		Name:          n.Sym().Name,
+		IsReturnValue: n.Class_ == ir.PPARAMOUT,
+		IsInlFormal:   n.Name().InlFormal(),
+		Abbrev:        abbrev,
+		StackOffset:   int32(offs),
+		Type:          base.Ctxt.Lookup(typename),
+		DeclFile:      declpos.RelFilename(),
+		DeclLine:      declpos.RelLine(),
+		DeclCol:       declpos.Col(),
+		InlIndex:      int32(inlIndex),
+		ChildIndex:    -1,
+	}
+}
+
+// createComplexVars creates recomposed DWARF vars with location lists,
+// suitable for describing optimized code.
+func createComplexVars(fnsym *obj.LSym, fn *ir.Func) ([]*ir.Name, []*dwarf.Var, map[*ir.Name]bool) {
+	debugInfo := fn.DebugInfo.(*ssa.FuncDebug)
+
+	// Produce a DWARF variable entry for each user variable.
+	var decls []*ir.Name
+	var vars []*dwarf.Var
+	ssaVars := make(map[*ir.Name]bool)
+
+	for varID, dvar := range debugInfo.Vars {
+		n := dvar
+		ssaVars[n] = true
+		for _, slot := range debugInfo.VarSlots[varID] {
+			ssaVars[debugInfo.Slots[slot].N] = true
+		}
+
+		if dvar := createComplexVar(fnsym, fn, ssa.VarID(varID)); dvar != nil {
+			decls = append(decls, n)
+			vars = append(vars, dvar)
+		}
+	}
+
+	return decls, vars, ssaVars
+}
+
+// createComplexVar builds a single DWARF variable entry and location list.
+func createComplexVar(fnsym *obj.LSym, fn *ir.Func, varID ssa.VarID) *dwarf.Var {
+	debug := fn.DebugInfo.(*ssa.FuncDebug)
+	n := debug.Vars[varID]
+
+	var abbrev int
+	switch n.Class_ {
+	case ir.PAUTO:
+		abbrev = dwarf.DW_ABRV_AUTO_LOCLIST
+	case ir.PPARAM, ir.PPARAMOUT:
+		abbrev = dwarf.DW_ABRV_PARAM_LOCLIST
+	default:
+		return nil
+	}
+
+	gotype := ngotype(n).Linksym()
+	delete(fnsym.Func().Autot, gotype)
+	typename := dwarf.InfoPrefix + gotype.Name[len("type."):]
+	inlIndex := 0
+	if base.Flag.GenDwarfInl > 1 {
+		if n.Name().InlFormal() || n.Name().InlLocal() {
+			inlIndex = posInlIndex(n.Pos()) + 1
+			if n.Name().InlFormal() {
+				abbrev = dwarf.DW_ABRV_PARAM_LOCLIST
+			}
+		}
+	}
+	declpos := base.Ctxt.InnermostPos(n.Pos())
+	dvar := &dwarf.Var{
+		Name:          n.Sym().Name,
+		IsReturnValue: n.Class_ == ir.PPARAMOUT,
+		IsInlFormal:   n.Name().InlFormal(),
+		Abbrev:        abbrev,
+		Type:          base.Ctxt.Lookup(typename),
+		// The stack offset is used as a sorting key, so for decomposed
+		// variables just give it the first one. It's not used otherwise.
+		// This won't work well if the first slot hasn't been assigned a stack
+		// location, but it's not obvious how to do better.
+		StackOffset: ssagen.StackOffset(debug.Slots[debug.VarSlots[varID][0]]),
+		DeclFile:    declpos.RelFilename(),
+		DeclLine:    declpos.RelLine(),
+		DeclCol:     declpos.Col(),
+		InlIndex:    int32(inlIndex),
+		ChildIndex:  -1,
+	}
+	list := debug.LocationLists[varID]
+	if len(list) != 0 {
+		dvar.PutLocationList = func(listSym, startPC dwarf.Sym) {
+			debug.PutLocationList(list, base.Ctxt, listSym.(*obj.LSym), startPC.(*obj.LSym))
+		}
+	}
+	return dvar
+}