cmd/compile: add R_USETYPE relocs to func syms for autom types

During DWARF processing, keep track of the go type symbols for types
directly or indirectly referenced by auto variables in a function,
and add a set of dummy R_USETYPE relocations to the function's DWARF
subprogram DIE symbol.

This change is not useful on its own, but is part of a series of
changes intended to clean up handling of autom's in the compiler
and linker.

Updates #34554.

Change-Id: I974afa9b7092aa5dba808f74e00aa931249d6fe9
Reviewed-on: https://go-review.googlesource.com/c/go/+/197497
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

src/cmd/compile/internal/gc/pgen.go

@@ -376,7 +376,7 @@ func compileFunctions() {
 	}
 }
 
-func debuginfo(fnsym *obj.LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls) {
+func debuginfo(fnsym *obj.LSym, infosym *obj.LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls) {
 	fn := curfn.(*Node)
 	if fn.Func.Nname != nil {
 		if expect := fn.Func.Nname.Sym.Linksym(); fnsym != expect {
@@ -414,10 +414,26 @@ func debuginfo(fnsym *obj.LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCall
 			Name:    name,
 			Gotype:  gotype,
 		})
+		fnsym.Func.RecordAutoType(gotype)
 	}
 
 	decls, dwarfVars := createDwarfVars(fnsym, fn.Func, automDecls)
 
+	// For each type referenced by the functions auto vars, attach a
+	// dummy 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 []ScopeID
 	for _, decl := range decls {
 		pos := decl.Pos
@@ -643,7 +659,7 @@ func createDwarfVars(fnsym *obj.LSym, fn *Func, automDecls []*Node) ([]*Node, []
 			Name:    obj.NAME_DELETED_AUTO,
 			Gotype:  gotype,
 		})
-
+		fnsym.Func.RecordAutoType(gotype)
 	}
 
 	return decls, vars

src/cmd/internal/obj/link.go

@@ -399,6 +399,7 @@ type FuncInfo struct {
 	Locals   int32
 	Text     *Prog
 	Autom    []*Auto
+	Autot    map[*LSym]struct{}
 	Pcln     Pcln
 	InlMarks []InlMark
 
@@ -431,6 +432,15 @@ func (fi *FuncInfo) AddInlMark(p *Prog, id int32) {
 	fi.InlMarks = append(fi.InlMarks, InlMark{p: p, id: id})
 }
 
+// Record the type symbol for an auto variable so that the linker
+// an emit DWARF type information for the type.
+func (fi *FuncInfo) RecordAutoType(gotype *LSym) {
+	if fi.Autot == nil {
+		fi.Autot = make(map[*LSym]struct{})
+	}
+	fi.Autot[gotype] = struct{}{}
+}
+
 //go:generate stringer -type ABI
 
 // ABI is the calling convention of a text symbol.
@@ -644,7 +654,7 @@ type Link struct {
 	Imports            []string
 	DiagFunc           func(string, ...interface{})
 	DiagFlush          func()
-	DebugInfo          func(fn *LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls) // if non-nil, curfn is a *gc.Node
+	DebugInfo          func(fn *LSym, info *LSym, curfn interface{}) ([]dwarf.Scope, dwarf.InlCalls) // if non-nil, curfn is a *gc.Node
 	GenAbstractFunc    func(fn *LSym)
 	Errors             int
 

src/cmd/internal/obj/objfile.go

@@ -597,7 +597,7 @@ func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym, myimportpath string)
 	var scopes []dwarf.Scope
 	var inlcalls dwarf.InlCalls
 	if ctxt.DebugInfo != nil {
-		scopes, inlcalls = ctxt.DebugInfo(s, curfn)
+		scopes, inlcalls = ctxt.DebugInfo(s, info, curfn)
 	}
 	var err error
 	dwctxt := dwCtxt{ctxt}
@@ -654,7 +654,7 @@ func (ctxt *Link) DwarfAbstractFunc(curfn interface{}, s *LSym, myimportpath str
 	if s.Func == nil {
 		s.Func = new(FuncInfo)
 	}
-	scopes, _ := ctxt.DebugInfo(s, curfn)
+	scopes, _ := ctxt.DebugInfo(s, absfn, curfn)
 	dwctxt := dwCtxt{ctxt}
 	filesym := ctxt.fileSymbol(s)
 	fnstate := dwarf.FnState{
@@ -893,7 +893,7 @@ func (ft *DwarfFixupTable) Finalize(myimportpath string, trace bool) {
 		fns[idx] = fn
 		idx++
 	}
-	sort.Sort(bySymName(fns))
+	sort.Sort(BySymName(fns))
 
 	// Should not be called during parallel portion of compilation.
 	if ft.ctxt.InParallel {
@@ -921,8 +921,8 @@ func (ft *DwarfFixupTable) Finalize(myimportpath string, trace bool) {
 	}
 }
 
-type bySymName []*LSym
+type BySymName []*LSym
 
-func (s bySymName) Len() int           { return len(s) }
-func (s bySymName) Less(i, j int) bool { return s[i].Name < s[j].Name }
-func (s bySymName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s BySymName) Len() int           { return len(s) }
+func (s BySymName) Less(i, j int) bool { return s[i].Name < s[j].Name }
+func (s BySymName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }