issue29362b.go

     1  // run
     2  
     3  // Copyright 2018 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  // Verify that we don't consider a Go'd function's
     8  // arguments as pointers when they aren't.
     9  
    10  package main
    11  
    12  import (
    13  	"unsafe"
    14  )
    15  
    16  var badPtr uintptr
    17  
    18  var sink []byte
    19  
    20  func init() {
    21  	// Allocate large enough to use largeAlloc.
    22  	b := make([]byte, 1<<16-1)
    23  	sink = b // force heap allocation
    24  	//  Any space between the object and the end of page is invalid to point to.
    25  	badPtr = uintptr(unsafe.Pointer(&b[len(b)-1])) + 1
    26  }
    27  
    28  var throttle = make(chan struct{}, 10)
    29  
    30  // There are 2 arg bitmaps for this function, each with 2 bits.
    31  // In the first, p and q are both live, so that bitmap is 11.
    32  // In the second, only p is live, so that bitmap is 10.
    33  // Bitmaps are byte aligned, so if the first bitmap is interpreted as
    34  // extending across the entire argument area, we incorrectly concatenate
    35  // the bitmaps and end up using 110000001. That bad bitmap causes a6
    36  // to be considered a pointer.
    37  func noPointerArgs(p, q *byte, a0, a1, a2, a3, a4, a5, a6 uintptr) {
    38  	sink = make([]byte, 4096)
    39  	sinkptr = q
    40  	<-throttle
    41  	sinkptr = p
    42  }
    43  
    44  var sinkptr *byte
    45  
    46  func main() {
    47  	const N = 1000
    48  	for i := 0; i < N; i++ {
    49  		throttle <- struct{}{}
    50  		go noPointerArgs(nil, nil, badPtr, badPtr, badPtr, badPtr, badPtr, badPtr, badPtr)
    51  		sink = make([]byte, 4096)
    52  	}
    53  }
    54
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