1 files changed, 176 insertions, 0 deletions
diff --git a/src/reflect/makefunc.go b/src/reflect/makefunc.go
new file mode 100644
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--- /dev/null
+++ b/src/reflect/makefunc.go
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+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// MakeFunc implementation.
+
+package reflect
+
+import (
+	"internal/abi"
+	"unsafe"
+)
+
+// makeFuncImpl is the closure value implementing the function
+// returned by MakeFunc.
+// The first three words of this type must be kept in sync with
+// methodValue and runtime.reflectMethodValue.
+// Any changes should be reflected in all three.
+type makeFuncImpl struct {
+	makeFuncCtxt
+	ftyp *funcType
+	fn   func([]Value) []Value
+}
+
+// MakeFunc returns a new function of the given Type
+// that wraps the function fn. When called, that new function
+// does the following:
+//
+//   - converts its arguments to a slice of Values.
+//   - runs results := fn(args).
+//   - returns the results as a slice of Values, one per formal result.
+//
+// The implementation fn can assume that the argument Value slice
+// has the number and type of arguments given by typ.
+// If typ describes a variadic function, the final Value is itself
+// a slice representing the variadic arguments, as in the
+// body of a variadic function. The result Value slice returned by fn
+// must have the number and type of results given by typ.
+//
+// The Value.Call method allows the caller to invoke a typed function
+// in terms of Values; in contrast, MakeFunc allows the caller to implement
+// a typed function in terms of Values.
+//
+// The Examples section of the documentation includes an illustration
+// of how to use MakeFunc to build a swap function for different types.
+func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value {
+	if typ.Kind() != Func {
+		panic("reflect: call of MakeFunc with non-Func type")
+	}
+
+	t := typ.common()
+	ftyp := (*funcType)(unsafe.Pointer(t))
+
+	code := abi.FuncPCABI0(makeFuncStub)
+
+	// makeFuncImpl contains a stack map for use by the runtime
+	_, _, abid := funcLayout(ftyp, nil)
+
+	impl := &makeFuncImpl{
+		makeFuncCtxt: makeFuncCtxt{
+			fn:      code,
+			stack:   abid.stackPtrs,
+			argLen:  abid.stackCallArgsSize,
+			regPtrs: abid.inRegPtrs,
+		},
+		ftyp: ftyp,
+		fn:   fn,
+	}
+
+	return Value{t, unsafe.Pointer(impl), flag(Func)}
+}
+
+// makeFuncStub is an assembly function that is the code half of
+// the function returned from MakeFunc. It expects a *callReflectFunc
+// as its context register, and its job is to invoke callReflect(ctxt, frame)
+// where ctxt is the context register and frame is a pointer to the first
+// word in the passed-in argument frame.
+func makeFuncStub()
+
+// The first 3 words of this type must be kept in sync with
+// makeFuncImpl and runtime.reflectMethodValue.
+// Any changes should be reflected in all three.
+type methodValue struct {
+	makeFuncCtxt
+	method int
+	rcvr   Value
+}
+
+// makeMethodValue converts v from the rcvr+method index representation
+// of a method value to an actual method func value, which is
+// basically the receiver value with a special bit set, into a true
+// func value - a value holding an actual func. The output is
+// semantically equivalent to the input as far as the user of package
+// reflect can tell, but the true func representation can be handled
+// by code like Convert and Interface and Assign.
+func makeMethodValue(op string, v Value) Value {
+	if v.flag&flagMethod == 0 {
+		panic("reflect: internal error: invalid use of makeMethodValue")
+	}
+
+	// Ignoring the flagMethod bit, v describes the receiver, not the method type.
+	fl := v.flag & (flagRO | flagAddr | flagIndir)
+	fl |= flag(v.typ().Kind())
+	rcvr := Value{v.typ(), v.ptr, fl}
+
+	// v.Type returns the actual type of the method value.
+	ftyp := (*funcType)(unsafe.Pointer(v.Type().(*rtype)))
+
+	code := methodValueCallCodePtr()
+
+	// methodValue contains a stack map for use by the runtime
+	_, _, abid := funcLayout(ftyp, nil)
+	fv := &methodValue{
+		makeFuncCtxt: makeFuncCtxt{
+			fn:      code,
+			stack:   abid.stackPtrs,
+			argLen:  abid.stackCallArgsSize,
+			regPtrs: abid.inRegPtrs,
+		},
+		method: int(v.flag) >> flagMethodShift,
+		rcvr:   rcvr,
+	}
+
+	// Cause panic if method is not appropriate.
+	// The panic would still happen during the call if we omit this,
+	// but we want Interface() and other operations to fail early.
+	methodReceiver(op, fv.rcvr, fv.method)
+
+	return Value{ftyp.Common(), unsafe.Pointer(fv), v.flag&flagRO | flag(Func)}
+}
+
+func methodValueCallCodePtr() uintptr {
+	return abi.FuncPCABI0(methodValueCall)
+}
+
+// methodValueCall is an assembly function that is the code half of
+// the function returned from makeMethodValue. It expects a *methodValue
+// as its context register, and its job is to invoke callMethod(ctxt, frame)
+// where ctxt is the context register and frame is a pointer to the first
+// word in the passed-in argument frame.
+func methodValueCall()
+
+// This structure must be kept in sync with runtime.reflectMethodValue.
+// Any changes should be reflected in all both.
+type makeFuncCtxt struct {
+	fn      uintptr
+	stack   *bitVector // ptrmap for both stack args and results
+	argLen  uintptr    // just args
+	regPtrs abi.IntArgRegBitmap
+}
+
+// moveMakeFuncArgPtrs uses ctxt.regPtrs to copy integer pointer arguments
+// in args.Ints to args.Ptrs where the GC can see them.
+//
+// This is similar to what reflectcallmove does in the runtime, except
+// that happens on the return path, whereas this happens on the call path.
+//
+// nosplit because pointers are being held in uintptr slots in args, so
+// having our stack scanned now could lead to accidentally freeing
+// memory.
+//
+//go:nosplit
+func moveMakeFuncArgPtrs(ctxt *makeFuncCtxt, args *abi.RegArgs) {
+	for i, arg := range args.Ints {
+		// Avoid write barriers! Because our write barrier enqueues what
+		// was there before, we might enqueue garbage.
+		if ctxt.regPtrs.Get(i) {
+			*(*uintptr)(unsafe.Pointer(&args.Ptrs[i])) = arg
+		} else {
+			// We *must* zero this space ourselves because it's defined in
+			// assembly code and the GC will scan these pointers. Otherwise,
+			// there will be garbage here.
+			*(*uintptr)(unsafe.Pointer(&args.Ptrs[i])) = 0
+		}
+	}
+}