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cmd/cgo: given typedef struct S T, make C.T and C.struct_S interchangeable

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For incomplete struct S, C.T and C.struct_S were interchangeable in Go 1.2
and earlier, because all incomplete types were interchangeable
(even C.struct_S1 and C.struct_S2).

CL 76450043, which fixed issue 7409, made different incomplete types
different from Go's point of view, so that they were no longer completely
interchangeable.

However, imprecision about C.T and C.struct_S - really the same
underlying C type - is the one behavior enabled by the bug that
is most likely to be depended on by existing cgo code.
Explicitly allow it, to keep that code working.

Fixes #7786.

LGTM=iant, r
R=golang-codereviews, iant, r
CC=golang-codereviews
https://golang.org/cl/98580046
This commit is contained in:
Russ Cox 2014-05-28 14:04:31 -04:00
parent 94849d5a78
commit 0782ee3ad5
3 changed files with 102 additions and 8 deletions
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51
src/cmd/cgo/gcc.go
View file

@ -1197,12 +1197,12 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
return t
case *dwarf.StructType:
if dt.ByteSize < 0 { // opaque struct
break
}
// Convert to Go struct, being careful about alignment.
// Have to give it a name to simulate C "struct foo" references.
tag := dt.StructName
if dt.ByteSize < 0 && tag == "" { // opaque unnamed struct - should not be possible
break
}
if tag == "" {
tag = "__" + strconv.Itoa(tagGen)
tagGen++
@ -1212,6 +1212,16 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
name := c.Ident("_Ctype_" + dt.Kind + "_" + tag)
t.Go = name // publish before recursive calls
goIdent[name.Name] = name
if dt.ByteSize < 0 {
// Size calculation in c.Struct/c.Opaque will die with size=-1 (unknown),
// so execute the basic things that the struct case would do
// other than try to determine a Go representation.
tt := *t
tt.C = &TypeRepr{"%s %s", []interface{}{dt.Kind, tag}}
tt.Go = c.Ident("struct{}")
typedef[name.Name] = &tt
break
}
switch dt.Kind {
case "class", "union":
t.Go = c.Opaque(t.Size)
@ -1264,7 +1274,12 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
tt.Go = sub.Go
typedef[name.Name] = &tt
}
if *godefs || *cdefs {
// If sub.Go.Name is "_Ctype_struct_foo" or "_Ctype_union_foo" or "_Ctype_class_foo",
// use that as the Go form for this typedef too, so that the typedef will be interchangeable
// with the base type.
// In -godefs and -cdefs mode, do this for all typedefs.
if isStructUnionClass(sub.Go) || *godefs || *cdefs {
t.Go = sub.Go
}
@ -1327,10 +1342,19 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
// be correct, so calling dtype.Size again will produce the correct value.
t.Size = dtype.Size()
if t.Size < 0 {
// Unsized types are [0]byte, unless they're typedefs of other types.
// if so, use the name of the typedef for the go name.
// Unsized types are [0]byte, unless they're typedefs of other types
// or structs with tags.
// if so, use the name we've already defined.
t.Size = 0
if _, ok := dtype.(*dwarf.TypedefType); !ok {
switch dt := dtype.(type) {
case *dwarf.TypedefType:
// ok
case *dwarf.StructType:
if dt.StructName != "" {
break
}
t.Go = c.Opaque(0)
default:
t.Go = c.Opaque(0)
}
if t.C.Empty() {
@ -1347,6 +1371,19 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
return t
}
// isStructUnionClass reports whether the type described by the Go syntax x
// is a struct, union, or class with a tag.
func isStructUnionClass(x ast.Expr) bool {
id, ok := x.(*ast.Ident)
if !ok {
return false
}
name := id.Name
return strings.HasPrefix(name, "_Ctype_struct_") ||
strings.HasPrefix(name, "_Ctype_union_") ||
strings.HasPrefix(name, "_Ctype_class_")
}
// FuncArg returns a Go type with the same memory layout as
// dtype when used as the type of a C function argument.
func (c *typeConv) FuncArg(dtype dwarf.Type, pos token.Pos) *Type {