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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))
// Indirect Go func value (dummy) to obtain
// actual code address. (A Go func value is a pointer
// to a C function pointer. https://golang.org/s/go11func.)
dummy := makeFuncStub
code := **(**uintptr)(unsafe.Pointer(&dummy))
// makeFuncImpl contains a stack map for use by the runtime
_, _, abi := funcLayout(ftyp, nil)
impl := &makeFuncImpl{
makeFuncCtxt: makeFuncCtxt{
fn: code,
stack: abi.stackPtrs,
argLen: abi.stackCallArgsSize,
regPtrs: abi.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)))
// Indirect Go func value (dummy) to obtain
// actual code address. (A Go func value is a pointer
// to a C function pointer. https://golang.org/s/go11func.)
dummy := methodValueCall
code := **(**uintptr)(unsafe.Pointer(&dummy))
// methodValue contains a stack map for use by the runtime
_, _, abi := funcLayout(ftyp, nil)
fv := &methodValue{
makeFuncCtxt: makeFuncCtxt{
fn: code,
stack: abi.stackPtrs,
argLen: abi.stackCallArgsSize,
regPtrs: abi.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.rtype, unsafe.Pointer(fv), v.flag&flagRO | flag(Func)}
}
// 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
}
}
}
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