1/*
2 * Copyright (C) 2010 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#ifndef PageReservation_h
27#define PageReservation_h
28
29#include <wtf/PageAllocation.h>
30
31namespace WTF {
32
33/*
34    PageReservation
35
36    Like PageAllocation, the PageReservation class provides a cross-platform memory
37    allocation interface, but with a set of capabilities more similar to that of
38    VirtualAlloc than posix mmap.  PageReservation can be used to allocate virtual
39    memory without committing physical memory pages using PageReservation::reserve.
40    Following a call to reserve all memory in the region is in a decommited state,
41    in which the memory should not be used (accessing the memory may cause a fault).
42
43    Before using memory it must be committed by calling commit, which is passed start
44    and size values (both of which require system page size granularity).  One the
45    committed memory is no longer needed 'decommit' may be called to return the
46    memory to its devommitted state.  Commit should only be called on memory that is
47    currently decommitted, and decommit should only be called on memory regions that
48    are currently committed.  All memory should be decommited before the reservation
49    is deallocated.  Values in memory may not be retained accross a pair of calls if
50    the region of memory is decommitted and then committed again.
51
52    Memory protection should not be changed on decommitted memory, and if protection
53    is changed on memory while it is committed it should be returned to the orignal
54    protection before decommit is called.
55*/
56
57class PageReservation : private PageBlock {
58public:
59    PageReservation()
60        : m_committed(0)
61        , m_writable(false)
62        , m_executable(false)
63    {
64    }
65
66    using PageBlock::base;
67    using PageBlock::size;
68
69#ifndef __clang__
70    using PageBlock::operator bool;
71#else
72    // FIXME: This is a workaround for <rdar://problem/8876150>, wherein Clang incorrectly emits an access
73    // control warning when a client tries to use operator bool exposed above via "using PageBlock::operator bool".
74    operator bool() const { return PageBlock::operator bool(); }
75#endif
76
77    void commit(void* start, size_t size)
78    {
79        ASSERT(*this);
80        ASSERT(isPageAligned(start));
81        ASSERT(isPageAligned(size));
82        ASSERT(contains(start, size));
83
84        m_committed += size;
85        OSAllocator::commit(start, size, m_writable, m_executable);
86    }
87
88    void decommit(void* start, size_t size)
89    {
90        ASSERT(*this);
91        ASSERT(isPageAligned(start));
92        ASSERT(isPageAligned(size));
93        ASSERT(contains(start, size));
94
95        m_committed -= size;
96        OSAllocator::decommit(start, size);
97    }
98
99    size_t committed()
100    {
101        return m_committed;
102    }
103
104    static PageReservation reserve(size_t size, OSAllocator::Usage usage = OSAllocator::UnknownUsage, bool writable = true, bool executable = false)
105    {
106        ASSERT(isPageAligned(size));
107        return PageReservation(OSAllocator::reserveUncommitted(size, usage, writable, executable), size, writable, executable, false);
108    }
109
110    static PageReservation reserveWithGuardPages(size_t size, OSAllocator::Usage usage = OSAllocator::UnknownUsage, bool writable = true, bool executable = false)
111    {
112        ASSERT(isPageAligned(size));
113        return PageReservation(OSAllocator::reserveUncommitted(size + pageSize() * 2, usage, writable, executable, true), size, writable, executable, true);
114    }
115
116    void deallocate()
117    {
118        ASSERT(!m_committed);
119
120        // Clear base & size before calling release; if this is *inside* allocation
121        // then we won't be able to clear then after deallocating the memory.
122        PageReservation tmp;
123        std::swap(tmp, *this);
124
125        ASSERT(tmp);
126        ASSERT(!*this);
127
128        OSAllocator::releaseDecommitted(tmp.base(), tmp.size());
129    }
130
131private:
132    PageReservation(void* base, size_t size, bool writable, bool executable, bool hasGuardPages)
133        : PageBlock(base, size, hasGuardPages)
134        , m_committed(0)
135        , m_writable(writable)
136        , m_executable(executable)
137    {
138    }
139
140    size_t m_committed;
141    bool m_writable;
142    bool m_executable;
143};
144
145}
146
147using WTF::PageReservation;
148
149#endif // PageReservation_h
150