go/src/reflect/export_test.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.
package reflect
// MakeRO returns a copy of v with the read-only flag set.
func MakeRO(v Value) Value {
v.flag |= flagRO
return v
}
// IsRO reports whether v's read-only flag is set.
func IsRO(v Value) bool {
return v.flag&flagRO != 0
}
var ArrayOf = arrayOf
reflect, runtime: fix crash in GC due to reflect.call + precise GC Given type Outer struct { *Inner ... } the compiler generates the implementation of (*Outer).M dispatching to the embedded Inner. The implementation is logically: func (p *Outer) M() { (p.Inner).M() } but since the only change here is the replacement of one pointer receiver with another, the actual generated code overwrites the original receiver with the p.Inner pointer and then jumps to the M method expecting the *Inner receiver. During reflect.Value.Call, we create an argument frame and the associated data structures to describe it to the garbage collector, populate the frame, call reflect.call to run a function call using that frame, and then copy the results back out of the frame. The reflect.call function does a memmove of the frame structure onto the stack (to set up the inputs), runs the call, and the memmoves the stack back to the frame structure (to preserve the outputs). Originally reflect.call did not distinguish inputs from outputs: both memmoves were for the full stack frame. However, in the case where the called function was one of these wrappers, the rewritten receiver is almost certainly a different type than the original receiver. This is not a problem on the stack, where we use the program counter to determine the type information and understand that during (*Outer).M the receiver is an *Outer while during (*Inner).M the receiver in the same memory word is now an *Inner. But in the statically typed argument frame created by reflect, the receiver is always an *Outer. Copying the modified receiver pointer off the stack into the frame will store an *Inner there, and then if a garbage collection happens to scan that argument frame before it is discarded, it will scan the *Inner memory as if it were an *Outer. If the two have different memory layouts, the collection will intepret the memory incorrectly. Fix by only copying back the results. Fixes #7725. LGTM=khr R=khr CC=dave, golang-codereviews https://golang.org/cl/85180043
2014-04-08 11:11:35 -04:00
var CallGC = &callGC
const PtrSize = ptrSize
const BitsPointer = bitsPointer
const BitsScalar = bitsScalar
func FuncLayout(t Type, rcvr Type) (frametype Type, argSize, retOffset uintptr, stack []byte, gc []byte, ptrs bool) {
var ft *rtype
var s *bitVector
if rcvr != nil {
ft, argSize, retOffset, s, _ = funcLayout(t.(*rtype), rcvr.(*rtype))
} else {
ft, argSize, retOffset, s, _ = funcLayout(t.(*rtype), nil)
}
frametype = ft
for i := uint32(0); i < s.n; i += 2 {
stack = append(stack, s.data[i/8]>>(i%8)&3)
}
if ft.kind&kindGCProg != 0 {
panic("can't handle gc programs")
}
gcdata := (*[1000]byte)(ft.gc[0])
for i := uintptr(0); i < ft.size/ptrSize; i++ {
gc = append(gc, gcdata[i/2]>>(i%2*4+2)&3)
}
ptrs = ft.kind&kindNoPointers == 0
return
}