compiler, runtime: Use function descriptors.

This changes the representation of a Go value of function type
from being a pointer to function code (like a C function
pointer) to being a pointer to a struct.  The first field of
the struct points to the function code.  The remaining fields,
if any, are the addresses of variables referenced in enclosing
functions.  For each call to a function, the address of the
function descriptor is passed as the last argument.

This lets us avoid generating trampolines, and removes the use
of writable/executable sections of the heap.

From-SVN: r200181

1 files changed, 31 insertions, 8 deletions

diff --git a/libgo/go/reflect/value.go b/libgo/go/reflect/value.go
index 15f5715..f8126e6 100644
--- a/libgo/go/reflect/value.go
+++ b/libgo/go/reflect/value.go
@@ -377,7 +377,7 @@ func (v Value) call(method string, in []Value) []Value {
 			if iface.itab == nil {
 				panic(method + " of method on nil interface value")
 			}
-			fn = iface.itab.fun[i]
+			fn = unsafe.Pointer(&iface.itab.fun[i])
 			rcvr = iface.word
 		} else {
 			ut := v.typ.uncommon()
@@ -388,7 +388,7 @@ func (v Value) call(method string, in []Value) []Value {
 			if m.pkgPath != nil {
 				panic(method + " of unexported method")
 			}
-			fn = m.tfn
+			fn = unsafe.Pointer(&m.tfn)
 			t = m.mtyp
 			rcvr = v.iword()
 		}
@@ -462,6 +462,10 @@ func (v Value) call(method string, in []Value) []Value {
 	if v.flag&flagMethod != 0 {
 		nin++
 	}
+	firstPointer := len(in) > 0 && Kind(t.In(0).(*rtype).kind) != Ptr && v.flag&flagMethod == 0 && isMethod(v.typ)
+	if v.flag&flagMethod == 0 && !firstPointer {
+		nin++
+	}
 	params := make([]unsafe.Pointer, nin)
 	off := 0
 	if v.flag&flagMethod != 0 {
@@ -471,7 +475,6 @@ func (v Value) call(method string, in []Value) []Value {
 		params[0] = unsafe.Pointer(p)
 		off = 1
 	}
-	first_pointer := false
 	for i, pv := range in {
 		pv.mustBeExported()
 		targ := t.In(i).(*rtype)
@@ -483,14 +486,17 @@ func (v Value) call(method string, in []Value) []Value {
 		} else {
 			params[off] = pv.val
 		}
-		if i == 0 && Kind(targ.kind) != Ptr && v.flag&flagMethod == 0 && isMethod(v.typ) {
+		if i == 0 && firstPointer {
 			p := new(unsafe.Pointer)
 			*p = params[off]
 			params[off] = unsafe.Pointer(p)
-			first_pointer = true
 		}
 		off++
 	}
+	if v.flag&flagMethod == 0 && !firstPointer {
+		// Closure argument.
+		params[off] = unsafe.Pointer(&fn)
+	}
 
 	ret := make([]Value, nout)
 	results := make([]unsafe.Pointer, nout)
@@ -509,7 +515,7 @@ func (v Value) call(method string, in []Value) []Value {
 		pr = &results[0]
 	}
 
-	call(t, fn, v.flag&flagMethod != 0, first_pointer, pp, pr)
+	call(t, fn, v.flag&flagMethod != 0, firstPointer, pp, pr)
 
 	return ret
 }
@@ -1209,18 +1215,35 @@ func (v Value) OverflowUint(x uint64) bool {
 // code using reflect cannot obtain unsafe.Pointers
 // without importing the unsafe package explicitly.
 // It panics if v's Kind is not Chan, Func, Map, Ptr, Slice, or UnsafePointer.
+//
+// If v's Kind is Func, the returned pointer is an underlying
+// code pointer, but not necessarily enough to identify a
+// single function uniquely. The only guarantee is that the
+// result is zero if and only if v is a nil func Value.
 func (v Value) Pointer() uintptr {
 	k := v.kind()
 	switch k {
-	case Chan, Func, Map, Ptr, UnsafePointer:
-		if k == Func && v.flag&flagMethod != 0 {
+	case Chan, Map, Ptr, UnsafePointer:
+		p := v.val
+		if v.flag&flagIndir != 0 {
+			p = *(*unsafe.Pointer)(p)
+		}
+		return uintptr(p)
+	case Func:
+		if v.flag&flagMethod != 0 {
 			panic("reflect.Value.Pointer of method Value")
 		}
 		p := v.val
 		if v.flag&flagIndir != 0 {
 			p = *(*unsafe.Pointer)(p)
 		}
+		// Non-nil func value points at data block.
+		// First word of data block is actual code.
+		if p != nil {
+			p = *(*unsafe.Pointer)(p)
+		}
 		return uintptr(p)
+
 	case Slice:
 		return (*SliceHeader)(v.val).Data
 	}