issue30041.go

     1  // run
     2  
     3  // Copyright 2019 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  // Issue 30041: copying results of a reflect-generated
     8  // call on stack should not have write barrier.
     9  
    10  package main
    11  
    12  import (
    13  	"reflect"
    14  	"runtime"
    15  	"unsafe"
    16  )
    17  
    18  var badPtr uintptr
    19  
    20  var sink []byte
    21  
    22  func init() {
    23  	// Allocate large enough to use largeAlloc.
    24  	b := make([]byte, 1<<16-1)
    25  	sink = b // force heap allocation
    26  	//  Any space between the object and the end of page is invalid to point to.
    27  	badPtr = uintptr(unsafe.Pointer(&b[len(b)-1])) + 1
    28  }
    29  
    30  type ft func() *int
    31  
    32  var fn ft
    33  
    34  func rf([]reflect.Value) []reflect.Value {
    35  	a := reflect.ValueOf((*int)(nil))
    36  	return []reflect.Value{a}
    37  }
    38  
    39  const N = 1000
    40  
    41  func main() {
    42  	fn = reflect.MakeFunc(reflect.TypeOf(fn), rf).Interface().(ft)
    43  
    44  	// Keep running GC so the write barrier is on.
    45  	go func() {
    46  		for i := 0; i < N; i++ {
    47  			runtime.GC()
    48  		}
    49  	}()
    50  
    51  	var x [10]uintptr
    52  	for i := range x {
    53  		x[i] = badPtr
    54  	}
    55  	for i := 0; i < N; i++ {
    56  		runtime.Gosched()
    57  		use(x) // prepare bad pointers on stack
    58  		fn()
    59  	}
    60  }
    61  
    62  //go:noinline
    63  func use([10]uintptr) {}
    64
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