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// $G $D/$F.go && $L $F.$A && ./$A.out

// Copyright 2011 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.

package main

import "unsafe"

// Having a big address space means that indexing
// at a 256 MB offset from a nil pointer might not
// cause a memory access fault. This test checks
// that Go is doing the correct explicit checks to catch
// these nil pointer accesses, not just relying on the hardware.
var dummy [256 << 20]byte // give us a big address space

func main() {
        // the test only tests what we intend to test
        // if dummy starts in the first 256 MB of memory.
        // otherwise there might not be anything mapped
        // at the address that might be accidentally
        // dereferenced below.
        if uintptr(unsafe.Pointer(&dummy)) > 256<<20 {
                panic("dummy too far out")
        }

        shouldPanic(p1)
        shouldPanic(p2)
        shouldPanic(p3)
        shouldPanic(p4)
        shouldPanic(p5)
        shouldPanic(p6)
        shouldPanic(p7)
        shouldPanic(p8)
        shouldPanic(p9)
        shouldPanic(p10)
}

func shouldPanic(f func()) {
        defer func() {
                if recover() == nil {
                        panic("memory reference did not panic")
                }
        }()
        f()
}

func p1() {
        // Array index.
        var p *[1 << 30]byte = nil
        println(p[256<<20]) // very likely to be inside dummy, but should panic
}

var xb byte

func p2() {
        var p *[1 << 30]byte = nil
        xb = 123

        // Array index.
        println(p[uintptr(unsafe.Pointer(&xb))]) // should panic
}

func p3() {
        // Array to slice.
        var p *[1 << 30]byte = nil
        var x []byte = p[0:] // should panic
        _ = x
}

var q *[1 << 30]byte

func p4() {
        // Array to slice.
        var x []byte
        var y = &x
        *y = q[0:] // should crash (uses arraytoslice runtime routine)
}

func fb([]byte) {
        panic("unreachable")
}

func p5() {
        // Array to slice.
        var p *[1 << 30]byte = nil
        fb(p[0:]) // should crash
}

func p6() {
        // Array to slice.
        var p *[1 << 30]byte = nil
        var _ []byte = p[10 : len(p)-10] // should crash
}

type T struct {
        x [256 << 20]byte
        i int
}

func f() *T {
        return nil
}

var y *T
var x = &y

func p7() {
        // Struct field access with large offset.
        println(f().i) // should crash
}

func p8() {
        // Struct field access with large offset.
        println((*x).i) // should crash
}

func p9() {
        // Struct field access with large offset.
        var t *T
        println(&t.i) // should crash
}

func p10() {
        // Struct field access with large offset.
        var t *T
        println(t.i) // should crash
}