...
Run Format

Source file test/fixedbugs/issue19078.go

Documentation: test/fixedbugs

  // run
  
  // Copyright 2017 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.
  
  // Issue 19078: liveness & zero-initialization of results
  // when there is a defer.
  package main
  
  import "unsafe"
  
  func main() {
  	// Construct an invalid pointer.  We do this by
  	// making a pointer which points to the unused space
  	// between the last 48-byte object in a span and the
  	// end of the span (there are 32 unused bytes there).
  	p := new([48]byte)              // make a 48-byte object
  	sink = &p                       // escape it, so it allocates for real
  	u := uintptr(unsafe.Pointer(p)) // get its address
  	u = u >> 13 << 13               // round down to page size
  	u += 1<<13 - 1                  // add almost a page
  
  	for i := 0; i < 1000000; i++ {
  		_ = identity(u)         // installs u at return slot
  		_ = liveReturnSlot(nil) // incorrectly marks return slot as live
  	}
  }
  
  //go:noinline
  func liveReturnSlot(x *int) *int {
  	defer func() {}() // causes return slot to be marked live
  	sink = &x         // causes x to be moved to the heap, triggering allocation
  	return x
  }
  
  //go:noinline
  func identity(x uintptr) uintptr {
  	return x
  }
  
  var sink interface{}
  

View as plain text