1 // run 2 3 // Copyright 2017 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 19078: liveness & zero-initialization of results 8 // when there is a defer. 9 package main 10 11 import "unsafe" 12 13 func main() { 14 // Construct an invalid pointer. We do this by 15 // making a pointer which points to the unused space 16 // between the last 48-byte object in a span and the 17 // end of the span (there are 32 unused bytes there). 18 p := new([48]byte) // make a 48-byte object 19 sink = &p // escape it, so it allocates for real 20 u := uintptr(unsafe.Pointer(p)) // get its address 21 u = u >> 13 << 13 // round down to page size 22 u += 1<<13 - 1 // add almost a page 23 24 for i := 0; i < 1000000; i++ { 25 _ = identity(u) // installs u at return slot 26 _ = liveReturnSlot(nil) // incorrectly marks return slot as live 27 } 28 } 29 30 //go:noinline 31 func liveReturnSlot(x *int) *int { 32 defer func() {}() // causes return slot to be marked live 33 sink = &x // causes x to be moved to the heap, triggering allocation 34 return x 35 } 36 37 //go:noinline 38 func identity(x uintptr) uintptr { 39 return x 40 } 41 42 var sink interface{} 43
