1// Copyright (C) 2016 The Qt Company Ltd.
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
3
4#include "qv4compilationunitmapper_p.h"
5
6#include <sys/mman.h>
7#include <functional>
8#include <private/qcore_unix_p.h>
9#include <QScopeGuard>
10#include <QDateTime>
11
12#include "qv4executablecompilationunit_p.h"
13
14QT_BEGIN_NAMESPACE
15
16using namespace QV4;
17
18CompiledData::Unit *CompilationUnitMapper::open(const QString &cacheFileName, const QDateTime &sourceTimeStamp, QString *errorString)
19{
20 close();
21
22 int fd = qt_safe_open(pathname: QFile::encodeName(fileName: cacheFileName).constData(), O_RDONLY);
23 if (fd == -1) {
24 *errorString = qt_error_string(errno);
25 return nullptr;
26 }
27
28 auto cleanup = qScopeGuard(f: [fd]{
29 qt_safe_close(fd) ;
30 });
31
32 CompiledData::Unit header;
33 qint64 bytesRead = qt_safe_read(fd, data: reinterpret_cast<char *>(&header), maxlen: sizeof(header));
34
35 if (bytesRead != sizeof(header)) {
36 *errorString = QStringLiteral("File too small for the header fields");
37 return nullptr;
38 }
39
40 if (!ExecutableCompilationUnit::verifyHeader(unit: &header, expectedSourceTimeStamp: sourceTimeStamp, errorString))
41 return nullptr;
42
43 // Data structure and qt version matched, so now we can access the rest of the file safely.
44
45 length = static_cast<size_t>(lseek(fd: fd, offset: 0, SEEK_END));
46
47 void *ptr = mmap(addr: nullptr, len: length, PROT_READ, MAP_SHARED, fd: fd, /*offset*/0);
48 if (ptr == MAP_FAILED) {
49 *errorString = qt_error_string(errno);
50 return nullptr;
51 }
52 dataPtr = ptr;
53
54 return reinterpret_cast<CompiledData::Unit*>(dataPtr);
55}
56
57void CompilationUnitMapper::close()
58{
59 // Do not unmap the data here.
60 if (dataPtr != nullptr) {
61 // Do not unmap cache files that are built with the StaticData flag. That's the majority of
62 // them and it's necessary to benefit from the QString literal optimization. There might
63 // still be QString instances around that point into that memory area. The memory is backed
64 // on the disk, so the kernel is free to release the pages and all that remains is the
65 // address space allocation.
66 if (!(reinterpret_cast<CompiledData::Unit*>(dataPtr)->flags & CompiledData::Unit::StaticData))
67 munmap(addr: dataPtr, len: length);
68 }
69 dataPtr = nullptr;
70}
71
72QT_END_NAMESPACE
73

source code of qtdeclarative/src/qml/jsruntime/qv4compilationunitmapper_unix.cpp