runtime: look up arg stackmap for makeFuncStub/methodValueStub during traceback

makeFuncStub and methodValueStub are used by reflect as
generic function implementations. Each call might have
different arguments. Extract those arguments from the
closure data instead of assuming it is the same each time.

Because the argument map is now being extracted from the
function itself, we don't need the special cases in reflect.Call
anymore, so delete those.

Fixes an occasional crash seen when stack copying does
not update makeFuncStub's arguments correctly.

Will also help make it safe to require stack maps in the
garbage collector.

Derived from CL 142000044 by khr.

LGTM=khr
R=khr
CC=golang-codereviews
https://codereview.appspot.com/143890044

1 files changed, 76 insertions, 6 deletions

diff --git a/src/reflect/type.go b/src/reflect/type.go
index 6817cd74d..67818f7f4 100644
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -242,7 +242,7 @@ const (
 // with a unique tag like `reflect:"array"` or `reflect:"ptr"`
 // so that code cannot convert from, say, *arrayType to *ptrType.
 type rtype struct {
-	size          uintptr           // size in bytes
+	size          uintptr
 	hash          uint32            // hash of type; avoids computation in hash tables
 	_             uint8             // unused/padding
 	align         uint8             // alignment of variable with this type
@@ -1726,6 +1726,7 @@ type layoutType struct {
 	t         *rtype
 	argSize   uintptr // size of arguments
 	retOffset uintptr // offset of return values.
+	stack     *bitVector
 }
 
 var layoutCache struct {
@@ -1739,7 +1740,7 @@ var layoutCache struct {
 // The returned type exists only for GC, so we only fill out GC relevant info.
 // Currently, that's just size and the GC program.  We also fill in
 // the name for possible debugging use.
-func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uintptr) {
+func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uintptr, stack *bitVector) {
 	if t.Kind() != Func {
 		panic("reflect: funcLayout of non-func type")
 	}
@@ -1750,19 +1751,21 @@ func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uin
 	layoutCache.RLock()
 	if x := layoutCache.m[k]; x.t != nil {
 		layoutCache.RUnlock()
-		return x.t, x.argSize, x.retOffset
+		return x.t, x.argSize, x.retOffset, x.stack
 	}
 	layoutCache.RUnlock()
 	layoutCache.Lock()
 	if x := layoutCache.m[k]; x.t != nil {
 		layoutCache.Unlock()
-		return x.t, x.argSize, x.retOffset
+		return x.t, x.argSize, x.retOffset, x.stack
 	}
 
 	tt := (*funcType)(unsafe.Pointer(t))
 
-	// compute gc program for arguments
+	// compute gc program & stack bitmap for arguments
+	stack = new(bitVector)
 	var gc gcProg
+	var offset uintptr
 	if rcvr != nil {
 		// Reflect uses the "interface" calling convention for
 		// methods, where receivers take one word of argument
@@ -1770,16 +1773,21 @@ func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uin
 		if !isDirectIface(rcvr) {
 			// we pass a pointer to the receiver.
 			gc.append(bitsPointer)
+			stack.append2(bitsPointer)
 		} else if rcvr.pointers() {
 			// rcvr is a one-word pointer object.  Its gc program
 			// is just what we need here.
 			gc.append(bitsPointer)
+			stack.append2(bitsPointer)
 		} else {
 			gc.append(bitsScalar)
+			stack.append2(bitsScalar)
 		}
+		offset += ptrSize
 	}
 	for _, arg := range tt.in {
 		gc.appendProg(arg)
+		addTypeBits(stack, &offset, arg)
 	}
 	argSize = gc.size
 	if runtime.GOARCH == "amd64p32" {
@@ -1789,6 +1797,7 @@ func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uin
 	retOffset = gc.size
 	for _, res := range tt.out {
 		gc.appendProg(res)
+		// stack map does not need result bits
 	}
 	gc.align(ptrSize)
 
@@ -1813,12 +1822,73 @@ func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uin
 		t:         x,
 		argSize:   argSize,
 		retOffset: retOffset,
+		stack:     stack,
 	}
 	layoutCache.Unlock()
-	return x, argSize, retOffset
+	return x, argSize, retOffset, stack
 }
 
 // isDirectIface reports whether t is stored directly in an interface value.
 func isDirectIface(t *rtype) bool {
 	return t.kind&kindDirectIface != 0
 }
+
+// Layout matches runtime.BitVector (well enough).
+type bitVector struct {
+	n    uint32 // number of bits
+	data []byte
+}
+
+// append a bit pair to the bitmap.
+func (bv *bitVector) append2(bits uint8) {
+	// assume bv.n is a multiple of 2, since append2 is the only operation.
+	if bv.n%8 == 0 {
+		bv.data = append(bv.data, 0)
+	}
+	bv.data[bv.n/8] |= bits << (bv.n % 8)
+	bv.n += 2
+}
+
+func addTypeBits(bv *bitVector, offset *uintptr, t *rtype) {
+	*offset = align(*offset, uintptr(t.align))
+	if t.kind&kindNoPointers != 0 {
+		*offset += t.size
+		return
+	}
+
+	switch Kind(t.kind & kindMask) {
+	case Chan, Func, Map, Ptr, Slice, String, UnsafePointer:
+		// 1 pointer at start of representation
+		for bv.n < uint32(*offset/uintptr(ptrSize)) {
+			bv.append2(bitsScalar)
+		}
+		bv.append2(bitsPointer)
+
+	case Interface:
+		// 2 pointers
+		for bv.n < uint32(*offset/uintptr(ptrSize)) {
+			bv.append2(bitsScalar)
+		}
+		bv.append2(bitsPointer)
+		bv.append2(bitsPointer)
+
+	case Array:
+		// repeat inner type
+		tt := (*arrayType)(unsafe.Pointer(t))
+		for i := 0; i < int(tt.len); i++ {
+			addTypeBits(bv, offset, tt.elem)
+		}
+
+	case Struct:
+		// apply fields
+		tt := (*structType)(unsafe.Pointer(t))
+		start := *offset
+		for i := range tt.fields {
+			f := &tt.fields[i]
+			off := start + f.offset
+			addTypeBits(bv, &off, f.typ)
+		}
+	}
+
+	*offset += t.size
+}