gocore: fix direct interface handling
An interface that contains a pointer-shaped type doesn't need to
introduce a new level of indirection, and is therefore called a "direct"
interface. The implementation of typeObject for direct interfaces was a
little over-eager, and tried to dereference that pointer before adding
it to the work queue.
That caused two problems. First, dereferencing a KindFunc is
meaningless: Funcs are pointers to closures, *not* the closures
themselves. Second, if it had failed to find the type of the interface
contents, notably because it had recursed through a struct type with no
DWARF, it would dereference unsafe.Pointer, end up with no type, and
crash.
The easiest fix is simply to not dereference the pointer. So do that,
and support KindFunc now that it'll work.
Change-Id: Ica03bd7155bea94d95a15807a977520958954b1c
Reviewed-on: https://go-review.googlesource.com/102195
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/gocore/type.go b/gocore/type.go
index 08b5cd1..49e6c64 100644
--- a/gocore/type.go
+++ b/gocore/type.go
@@ -530,39 +530,49 @@
case KindEface, KindIface:
// interface. Use the type word to determine the type
// of the pointed-to object.
- typ := r.ReadPtr(a)
- if typ == 0 { // nil interface
+ typPtr := r.ReadPtr(a)
+ if typPtr == 0 { // nil interface
return
}
- ptr := r.ReadPtr(a.Add(ptrSize))
+ data := a.Add(ptrSize)
if t.Kind == KindIface {
- typ = p.proc.ReadPtr(typ.Add(p.findType("runtime.itab").field("_type").Off))
+ typPtr = p.proc.ReadPtr(typPtr.Add(p.findType("runtime.itab").field("_type").Off))
}
- // TODO: for KindEface, type the typ pointer. It might point to the heap
+ // TODO: for KindEface, type typPtr. It might point to the heap
// if the type was allocated with reflect.
- dt := p.runtimeType2Type(typ)
- typr := region{p: p, a: typ, typ: p.findType("runtime._type")}
- if typr.Field("kind").Uint8()&uint8(p.rtConstants["kindDirectIface"]) != 0 {
- // Find the base type of the pointer held in the interface.
- findptr:
- if dt.Kind == KindArray {
- dt = dt.Elem
- goto findptr
+ typ := p.runtimeType2Type(typPtr)
+ typr := region{p: p, a: typPtr, typ: p.findType("runtime._type")}
+ if typr.Field("kind").Uint8()&uint8(p.rtConstants["kindDirectIface"]) == 0 {
+ // Indirect interface: the interface introduced a new
+ // level of indirection, not reflected in the type.
+ // Read through it.
+ add(r.ReadPtr(data), typ, 1)
+ return
+ }
+
+ // Direct interface: the contained type is a single pointer.
+ // Figure out what it is and type it. See isdirectiface() for the rules.
+ directTyp := typ
+ findDirect:
+ for {
+ if directTyp.Kind == KindArray {
+ directTyp = typ.Elem
+ continue findDirect
}
- if dt.Kind == KindStruct {
- for _, f := range dt.Fields {
+ if directTyp.Kind == KindStruct {
+ for _, f := range directTyp.Fields {
if f.Type.Size != 0 {
- dt = f.Type
- goto findptr
+ directTyp = f.Type
+ continue findDirect
}
}
}
- if dt.Kind != KindPtr {
- panic(fmt.Sprintf("direct type isn't a pointer %s", dt.Kind))
+ if directTyp.Kind != KindFunc && directTyp.Kind != KindPtr {
+ panic(fmt.Sprintf("type of direct interface, originally %s (kind %s), isn't a pointer: %s (kind %s)", typ, typ.Kind, directTyp, directTyp.Kind))
}
- dt = dt.Elem
+ break
}
- add(ptr, dt, 1)
+ add(data, directTyp, 1)
case KindString:
ptr := r.ReadPtr(a)
len := r.ReadInt(a.Add(ptrSize))
