cgo: fix dwarf type parsing

The recursive algorithm used to parse types in cgo
has a bug related to building the C type representation.

As an example, when the recursion starts at a type *T,
the C type representation won't be known until type T
itself is parsed.  But then, it is possible that type T
references the type **T internally.  The latter
representation is built based on the one of *T, which
started the recursion, so it won't attempt to parse it
again, and will instead use the current representation
value for *T, which is still empty at this point.

This problem was fixed by introducing a simple TypeRepr
type which builds the string representation lazily,
analogous to how the Go type information is built within
the same algorithm.  This way, even if a type
representation is still unknown at some level in the
recursion, representations dependant on it can still
be created correctly.

R=rsc
CC=golang-dev
https://golang.org/cl/4244052

3 files changed, 85 insertions, 48 deletions

diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index cc570f9cf3..f7ecc9e14e 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -776,6 +776,32 @@ var dwarfToName = map[string]string{
 
 const signedDelta = 64
 
+// String returns the current type representation.  Format arguments
+// are assembled within this method so that any changes in mutable
+// values are taken into account.
+func (tr *TypeRepr) String() string {
+	if len(tr.Repr) == 0 {
+		return ""
+	}
+	if len(tr.FormatArgs) == 0 {
+		return tr.Repr
+	}
+	return fmt.Sprintf(tr.Repr, tr.FormatArgs...)
+}
+
+// Empty returns true if the result of String would be "".
+func (tr *TypeRepr) Empty() bool {
+	return len(tr.Repr) == 0
+}
+
+// Set modifies the type representation.
+// If fargs are provided, repr is used as a format for fmt.Sprintf.
+// Otherwise, repr is used unprocessed as the type representation.
+func (tr *TypeRepr) Set(repr string, fargs ...interface{}) {
+	tr.Repr = repr
+	tr.FormatArgs = fargs
+}
+
 // Type returns a *Type with the same memory layout as
 // dtype when used as the type of a variable or a struct field.
 func (c *typeConv) Type(dtype dwarf.Type) *Type {
@@ -789,16 +815,15 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 	t := new(Type)
 	t.Size = dtype.Size()
 	t.Align = -1
-	t.C = dtype.Common().Name
-	t.EnumValues = nil
+	t.C = &TypeRepr{Repr: dtype.Common().Name}
 	c.m[dtype] = t
 
 	if t.Size < 0 {
 		// Unsized types are [0]byte
 		t.Size = 0
 		t.Go = c.Opaque(0)
-		if t.C == "" {
-			t.C = "void"
+		if t.C.Empty() {
+			t.C.Set("void")
 		}
 		return t
 	}
@@ -827,7 +852,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 		sub := c.Type(dt.Type)
 		t.Align = sub.Align
 		gt.Elt = sub.Go
-		t.C = fmt.Sprintf("typeof(%s[%d])", sub.C, dt.Count)
+		t.C.Set("typeof(%s[%d])", sub.C, dt.Count)
 
 	case *dwarf.BoolType:
 		t.Go = c.bool
@@ -844,7 +869,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 		if t.Align = t.Size; t.Align >= c.ptrSize {
 			t.Align = c.ptrSize
 		}
-		t.C = "enum " + dt.EnumName
+		t.C.Set("enum " + dt.EnumName)
 		signed := 0
 		t.EnumValues = make(map[string]int64)
 		for _, ev := range dt.Val {
@@ -932,7 +957,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 		// Translate void* as unsafe.Pointer
 		if _, ok := base(dt.Type).(*dwarf.VoidType); ok {
 			t.Go = c.unsafePointer
-			t.C = "void*"
+			t.C.Set("void*")
 			break
 		}
 
@@ -940,7 +965,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 		t.Go = gt // publish before recursive call
 		sub := c.Type(dt.Type)
 		gt.X = sub.Go
-		t.C = sub.C + "*"
+		t.C.Set("%s*", sub.C)
 
 	case *dwarf.QualType:
 		// Ignore qualifier.
@@ -955,21 +980,21 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 		if tag == "" {
 			tag = "__" + strconv.Itoa(tagGen)
 			tagGen++
-		} else if t.C == "" {
-			t.C = dt.Kind + " " + tag
+		} else if t.C.Empty() {
+			t.C.Set(dt.Kind + " " + tag)
 		}
 		name := c.Ident("_Ctype_" + dt.Kind + "_" + tag)
 		t.Go = name // publish before recursive calls
 		switch dt.Kind {
 		case "union", "class":
 			typedef[name.Name] = c.Opaque(t.Size)
-			if t.C == "" {
-				t.C = fmt.Sprintf("typeof(unsigned char[%d])", t.Size)
+			if t.C.Empty() {
+				t.C.Set("typeof(unsigned char[%d])", t.Size)
 			}
 		case "struct":
 			g, csyntax, align := c.Struct(dt)
-			if t.C == "" {
-				t.C = csyntax
+			if t.C.Empty() {
+				t.C.Set(csyntax)
 			}
 			t.Align = align
 			typedef[name.Name] = g
@@ -1024,7 +1049,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 
 	case *dwarf.VoidType:
 		t.Go = c.void
-		t.C = "void"
+		t.C.Set("void")
 	}
 
 	switch dtype.(type) {
@@ -1041,7 +1066,7 @@ func (c *typeConv) Type(dtype dwarf.Type) *Type {
 		}
 	}
 
-	if t.C == "" {
+	if t.C.Empty() {
 		fatal("internal error: did not create C name for %s", dtype)
 	}
 
@@ -1056,11 +1081,13 @@ func (c *typeConv) FuncArg(dtype dwarf.Type) *Type {
 	case *dwarf.ArrayType:
 		// Arrays are passed implicitly as pointers in C.
 		// In Go, we must be explicit.
+		tr := &TypeRepr{}
+		tr.Set("%s*", t.C)
 		return &Type{
 			Size:  c.ptrSize,
 			Align: c.ptrSize,
 			Go:    &ast.StarExpr{X: t.Go},
-			C:     t.C + "*",
+			C:     tr,
 		}
 	case *dwarf.TypedefType:
 		// C has much more relaxed rules than Go for
@@ -1189,7 +1216,7 @@ func (c *typeConv) Struct(dt *dwarf.StructType) (expr *ast.StructType, csyntax s
 
 		fld[n] = &ast.Field{Names: []*ast.Ident{c.Ident(ident[f.Name])}, Type: t.Go}
 		off += t.Size
-		buf.WriteString(t.C)
+		buf.WriteString(t.C.String())
 		buf.WriteString(" ")
 		buf.WriteString(f.Name)
 		buf.WriteString("; ")
diff --git a/src/cmd/cgo/main.go b/src/cmd/cgo/main.go
index dbf0664dce..2dc662de54 100644
--- a/src/cmd/cgo/main.go
+++ b/src/cmd/cgo/main.go
@@ -82,11 +82,17 @@ type ExpFunc struct {
 	ExpName string // name to use from C
 }
 
+// A TypeRepr contains the string representation of a type.
+type TypeRepr struct {
+	Repr       string
+	FormatArgs []interface{}
+}
+
 // A Type collects information about a type in both the C and Go worlds.
 type Type struct {
 	Size       int64
 	Align      int64
-	C          string
+	C          *TypeRepr
 	Go         ast.Expr
 	EnumValues map[string]int64
 }
diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 4d903dbeeb..4a5fa6a73f 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -163,7 +163,7 @@ func (p *Package) structType(n *Name) (string, int64) {
 			off += pad
 		}
 		qual := ""
-		if t.C[len(t.C)-1] == '*' {
+		if c := t.C.String(); c[len(c)-1] == '*' {
 			qual = "const "
 		}
 		fmt.Fprintf(&buf, "\t\t%s%s r;\n", qual, t.C)
@@ -403,7 +403,7 @@ func (p *Package) writeExports(fgo2, fc, fm *os.File) {
 		if fntype.Results == nil || len(fntype.Results.List) == 0 {
 			gccResult = "void"
 		} else if len(fntype.Results.List) == 1 && len(fntype.Results.List[0].Names) <= 1 {
-			gccResult = p.cgoType(fntype.Results.List[0].Type).C
+			gccResult = p.cgoType(fntype.Results.List[0].Type).C.String()
 		} else {
 			fmt.Fprintf(fgcch, "\n/* Return type for %s */\n", exp.ExpName)
 			fmt.Fprintf(fgcch, "struct %s_return {\n", exp.ExpName)
@@ -418,7 +418,7 @@ func (p *Package) writeExports(fgo2, fc, fm *os.File) {
 		// Build the wrapper function compiled by gcc.
 		s := fmt.Sprintf("%s %s(", gccResult, exp.ExpName)
 		if fn.Recv != nil {
-			s += p.cgoType(fn.Recv.List[0].Type).C
+			s += p.cgoType(fn.Recv.List[0].Type).C.String()
 			s += " recv"
 		}
 		forFieldList(fntype.Params,
@@ -534,24 +534,28 @@ func forFieldList(fl *ast.FieldList, fn func(int, ast.Expr)) {
 	}
 }
 
+func c(repr string, args ...interface{}) *TypeRepr {
+	return &TypeRepr{repr, args}
+}
+
 // Map predeclared Go types to Type.
 var goTypes = map[string]*Type{
-	"int":        &Type{Size: 4, Align: 4, C: "int"},
-	"uint":       &Type{Size: 4, Align: 4, C: "uint"},
-	"int8":       &Type{Size: 1, Align: 1, C: "schar"},
-	"uint8":      &Type{Size: 1, Align: 1, C: "uchar"},
-	"int16":      &Type{Size: 2, Align: 2, C: "short"},
-	"uint16":     &Type{Size: 2, Align: 2, C: "ushort"},
-	"int32":      &Type{Size: 4, Align: 4, C: "int"},
-	"uint32":     &Type{Size: 4, Align: 4, C: "uint"},
-	"int64":      &Type{Size: 8, Align: 8, C: "int64"},
-	"uint64":     &Type{Size: 8, Align: 8, C: "uint64"},
-	"float":      &Type{Size: 4, Align: 4, C: "float"},
-	"float32":    &Type{Size: 4, Align: 4, C: "float"},
-	"float64":    &Type{Size: 8, Align: 8, C: "double"},
-	"complex":    &Type{Size: 8, Align: 8, C: "__complex float"},
-	"complex64":  &Type{Size: 8, Align: 8, C: "__complex float"},
-	"complex128": &Type{Size: 16, Align: 16, C: "__complex double"},
+	"int":        &Type{Size: 4, Align: 4, C: c("int")},
+	"uint":       &Type{Size: 4, Align: 4, C: c("uint")},
+	"int8":       &Type{Size: 1, Align: 1, C: c("schar")},
+	"uint8":      &Type{Size: 1, Align: 1, C: c("uchar")},
+	"int16":      &Type{Size: 2, Align: 2, C: c("short")},
+	"uint16":     &Type{Size: 2, Align: 2, C: c("ushort")},
+	"int32":      &Type{Size: 4, Align: 4, C: c("int")},
+	"uint32":     &Type{Size: 4, Align: 4, C: c("uint")},
+	"int64":      &Type{Size: 8, Align: 8, C: c("int64")},
+	"uint64":     &Type{Size: 8, Align: 8, C: c("uint64")},
+	"float":      &Type{Size: 4, Align: 4, C: c("float")},
+	"float32":    &Type{Size: 4, Align: 4, C: c("float")},
+	"float64":    &Type{Size: 8, Align: 8, C: c("double")},
+	"complex":    &Type{Size: 8, Align: 8, C: c("__complex float")},
+	"complex64":  &Type{Size: 8, Align: 8, C: c("__complex float")},
+	"complex128": &Type{Size: 16, Align: 16, C: c("__complex double")},
 }
 
 // Map an ast type to a Type.
@@ -559,21 +563,21 @@ func (p *Package) cgoType(e ast.Expr) *Type {
 	switch t := e.(type) {
 	case *ast.StarExpr:
 		x := p.cgoType(t.X)
-		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: x.C + "*"}
+		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("%s*", x.C)}
 	case *ast.ArrayType:
 		if t.Len == nil {
-			return &Type{Size: p.PtrSize + 8, Align: p.PtrSize, C: "GoSlice"}
+			return &Type{Size: p.PtrSize + 8, Align: p.PtrSize, C: c("GoSlice")}
 		}
 	case *ast.StructType:
 		// TODO
 	case *ast.FuncType:
-		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: "void*"}
+		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("void*")}
 	case *ast.InterfaceType:
-		return &Type{Size: 3 * p.PtrSize, Align: p.PtrSize, C: "GoInterface"}
+		return &Type{Size: 3 * p.PtrSize, Align: p.PtrSize, C: c("GoInterface")}
 	case *ast.MapType:
-		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: "GoMap"}
+		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoMap")}
 	case *ast.ChanType:
-		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: "GoChan"}
+		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoChan")}
 	case *ast.Ident:
 		// Look up the type in the top level declarations.
 		// TODO: Handle types defined within a function.
@@ -598,10 +602,10 @@ func (p *Package) cgoType(e ast.Expr) *Type {
 			}
 		}
 		if t.Name == "uintptr" {
-			return &Type{Size: p.PtrSize, Align: p.PtrSize, C: "uintptr"}
+			return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("uintptr")}
 		}
 		if t.Name == "string" {
-			return &Type{Size: p.PtrSize + 4, Align: p.PtrSize, C: "GoString"}
+			return &Type{Size: p.PtrSize + 4, Align: p.PtrSize, C: c("GoString")}
 		}
 		if r, ok := goTypes[t.Name]; ok {
 			if r.Align > p.PtrSize {
@@ -612,11 +616,11 @@ func (p *Package) cgoType(e ast.Expr) *Type {
 	case *ast.SelectorExpr:
 		id, ok := t.X.(*ast.Ident)
 		if ok && id.Name == "unsafe" && t.Sel.Name == "Pointer" {
-			return &Type{Size: p.PtrSize, Align: p.PtrSize, C: "void*"}
+			return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("void*")}
 		}
 	}
 	error(e.Pos(), "unrecognized Go type %T", e)
-	return &Type{Size: 4, Align: 4, C: "int"}
+	return &Type{Size: 4, Align: 4, C: c("int")}
 }
 
 const gccProlog = `