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