unsafe_test.go

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package main
     6  
     7  import (
     8  	"runtime"
     9  	"testing"
    10  	"unsafe"
    11  )
    12  
    13  // global pointer slot
    14  var a *[8]uint
    15  
    16  // unfoldable true
    17  var always = true
    18  
    19  // Test to make sure that a pointer value which is alive
    20  // across a call is retained, even when there are matching
    21  // conversions to/from uintptr around the call.
    22  // We arrange things very carefully to have to/from
    23  // conversions on either side of the call which cannot be
    24  // combined with any other conversions.
    25  func f_ssa() *[8]uint {
    26  	// Make x a uintptr pointing to where a points.
    27  	var x uintptr
    28  	if always {
    29  		x = uintptr(unsafe.Pointer(a))
    30  	} else {
    31  		x = 0
    32  	}
    33  	// Clobber the global pointer. The only live ref
    34  	// to the allocated object is now x.
    35  	a = nil
    36  
    37  	// Convert to pointer so it should hold
    38  	// the object live across GC call.
    39  	p := unsafe.Pointer(x)
    40  
    41  	// Call gc.
    42  	runtime.GC()
    43  
    44  	// Convert back to uintptr.
    45  	y := uintptr(p)
    46  
    47  	// Mess with y so that the subsequent cast
    48  	// to unsafe.Pointer can't be combined with the
    49  	// uintptr cast above.
    50  	var z uintptr
    51  	if always {
    52  		z = y
    53  	} else {
    54  		z = 0
    55  	}
    56  	return (*[8]uint)(unsafe.Pointer(z))
    57  }
    58  
    59  // g_ssa is the same as f_ssa, but with a bit of pointer
    60  // arithmetic for added insanity.
    61  func g_ssa() *[7]uint {
    62  	// Make x a uintptr pointing to where a points.
    63  	var x uintptr
    64  	if always {
    65  		x = uintptr(unsafe.Pointer(a))
    66  	} else {
    67  		x = 0
    68  	}
    69  	// Clobber the global pointer. The only live ref
    70  	// to the allocated object is now x.
    71  	a = nil
    72  
    73  	// Offset x by one int.
    74  	x += unsafe.Sizeof(int(0))
    75  
    76  	// Convert to pointer so it should hold
    77  	// the object live across GC call.
    78  	p := unsafe.Pointer(x)
    79  
    80  	// Call gc.
    81  	runtime.GC()
    82  
    83  	// Convert back to uintptr.
    84  	y := uintptr(p)
    85  
    86  	// Mess with y so that the subsequent cast
    87  	// to unsafe.Pointer can't be combined with the
    88  	// uintptr cast above.
    89  	var z uintptr
    90  	if always {
    91  		z = y
    92  	} else {
    93  		z = 0
    94  	}
    95  	return (*[7]uint)(unsafe.Pointer(z))
    96  }
    97  
    98  func testf(t *testing.T) {
    99  	a = new([8]uint)
   100  	for i := 0; i < 8; i++ {
   101  		a[i] = 0xabcd
   102  	}
   103  	c := f_ssa()
   104  	for i := 0; i < 8; i++ {
   105  		if c[i] != 0xabcd {
   106  			t.Fatalf("%d:%x\n", i, c[i])
   107  		}
   108  	}
   109  }
   110  
   111  func testg(t *testing.T) {
   112  	a = new([8]uint)
   113  	for i := 0; i < 8; i++ {
   114  		a[i] = 0xabcd
   115  	}
   116  	c := g_ssa()
   117  	for i := 0; i < 7; i++ {
   118  		if c[i] != 0xabcd {
   119  			t.Fatalf("%d:%x\n", i, c[i])
   120  		}
   121  	}
   122  }
   123  
   124  func alias_ssa(ui64 *uint64, ui32 *uint32) uint32 {
   125  	*ui32 = 0xffffffff
   126  	*ui64 = 0                  // store
   127  	ret := *ui32               // load from same address, should be zero
   128  	*ui64 = 0xffffffffffffffff // store
   129  	return ret
   130  }
   131  func testdse(t *testing.T) {
   132  	x := int64(-1)
   133  	// construct two pointers that alias one another
   134  	ui64 := (*uint64)(unsafe.Pointer(&x))
   135  	ui32 := (*uint32)(unsafe.Pointer(&x))
   136  	if want, got := uint32(0), alias_ssa(ui64, ui32); got != want {
   137  		t.Fatalf("alias_ssa: wanted %d, got %d\n", want, got)
   138  	}
   139  }
   140  
   141  func TestUnsafe(t *testing.T) {
   142  	testf(t)
   143  	testg(t)
   144  	testdse(t)
   145  }
   146
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