1// Copyright (C) 2022 Intel Corporation.
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
3
4#if !defined(QVERSIONTAGGING_H)
5#define QVERSIONTAGGING_H
6
7#include <QtCore/qcompilerdetection.h>
8#include <QtCore/qtconfigmacros.h>
9#include <QtCore/qtversionchecks.h>
10#include <QtCore/qtypes.h>
11
12QT_BEGIN_NAMESPACE
13
14/*
15 * Explanation
16 *
17 * This file causes all libraries, plugins, and applications that #include this
18 * file to automatically pull in a symbol found in QtCore that encodes the
19 * current Qt version number at the time of compilation. The relocation is
20 * designed so that it's impossible for the dynamic linker to perform lazy
21 * binding. Instead, it must resolve at load time or fail. That way, attempting
22 * to load such a library or plugin while an older QtCore is loaded will fail.
23 * Similarly, if an older QtCore is found when launching an application, the
24 * application will fail to launch.
25 *
26 * It's also possible to inspect which version is required by decoding the
27 * .qtversion section. The second pointer-sized variable is the required
28 * version, for example, for Qt 6.4.1:
29 *
30 * Hex dump of section [18] '.qtversion', 16 bytes at offset 0x1ee48:
31 * 0x00000000 b0ffffff ffffffff 01040600 00000000 ................
32 * ^^^^^^^^ ^^^^^^^^
33 *
34 * There will only be one copy of the section in the output library or application.
35 *
36 * This functionality can be disabled by defining QT_NO_VERSION_TAGGING. It's
37 * disabled if Qt was built statically.
38 *
39 * Windows notes:
40 *
41 * On Windows, the address of a __declspec(dllimport) variable is not a
42 * constant expression, unlike Unix systems. So we instead use the address of
43 * the import variable, which is created by prefixing the external name with
44 * "__imp_". Using that variable causes an import of the corresponding symbol
45 * from QtCore DLL.
46 *
47 * With MinGW (GCC and Clang), we use a C++17 inline variable, so the compiler
48 * and linker automatically merge the variables. The "used" __attribute__
49 * tells the compiler to always emit that variable, whether it's used or not.
50 *
51 * MSVC has no equivalent to that attribute, so instead we create an extern
52 * const variable and tell the linker to merge them all via
53 * __declspec(selectany).
54 *
55 * Unix notes:
56 *
57 * On Unix, we use the same C++17 inline variable solution as MinGW, but we
58 * don't need the "__imp_" trick.
59 *
60 * Additionally, on ELF systems like Linux and FreeBSD, the symbol in question
61 * is simply "qt_version_tag" in both QtCore and in this ELF module, but it
62 * has an ELF version attached to it (see qversiontagging.cpp and
63 * QtFlagHandlingHelpers.cmake). That way, the error message from the dynamic
64 * linker will say it can't find version "Qt_6.x".
65 */
66
67namespace QtPrivate {
68struct QVersionTag
69{
70 const void *symbol;
71 quintptr version;
72 constexpr QVersionTag(const void *sym, int currentVersion = QT_VERSION)
73 : symbol(sym), version(currentVersion)
74 {}
75};
76}
77
78#if !defined(QT_NO_VERSION_TAGGING) && (defined(QT_BUILD_CORE_LIB) || defined(QT_BOOTSTRAPPED) || defined(QT_STATIC))
79// don't make tags in QtCore, bootstrapped systems or if the user asked not to
80# define QT_NO_VERSION_TAGGING
81#endif
82
83#if defined(Q_OS_WIN)
84# ifdef Q_PROCESSOR_X86_32
85// 32-bit x86 convention does prepend a _
86# define QT_MANGLE_IMPORT_PREFIX _imp__
87# else
88// Calling convention on other architectures does not prepend a _
89# define QT_MANGLE_IMPORT_PREFIX __imp_
90# endif
91# if defined(Q_CC_MSVC_ONLY)
92# pragma section(".qtversion",read,shared)
93# define QT_VERSION_TAG_SECTION __declspec(allocate(".qtversion"))
94# define QT_VERSION_TAG_ATTRIBUTE __declspec(selectany) extern const
95# else
96# define QT_VERSION_TAG_ATTRIBUTE __attribute__((used)) constexpr inline
97# endif
98# define QT_VERSION_TAG2(sym, imp) \
99 extern "C" const char * const imp; \
100 QT_VERSION_TAG_ATTRIBUTE QT_VERSION_TAG_SECTION QtPrivate::QVersionTag sym ## _used(&imp)
101# define QT_VERSION_TAG(sym, imp) QT_VERSION_TAG2(sym, imp)
102#elif defined(Q_CC_GNU) && __has_attribute(used)
103# ifdef Q_OS_DARWIN
104# define QT_VERSION_TAG_SECTION __attribute__((section("__DATA,.qtversion")))
105# endif
106# define QT_VERSION_TAG_ATTRIBUTE __attribute__((visibility("hidden"), used))
107# define QT_VERSION_TAG2(sym, imp) \
108 extern "C" Q_DECL_IMPORT const char sym; \
109 QT_VERSION_TAG_ATTRIBUTE QT_VERSION_TAG_SECTION constexpr inline QtPrivate::QVersionTag sym ## _use(&sym)
110# define QT_VERSION_TAG(sym, imp) QT_VERSION_TAG2(sym, imp)
111#endif
112
113#ifdef Q_OF_ELF
114# define QT_VERSION_TAG_SYMBOL(prefix, sym, m, n) sym
115#else
116# define QT_VERSION_TAG_SYMBOL2(prefix, sym, m, n) prefix ## sym ## _ ## m ## _ ## n
117# define QT_VERSION_TAG_SYMBOL(prefix, sym, m, n) QT_VERSION_TAG_SYMBOL2(prefix, sym, m, n)
118#endif
119
120#if defined(QT_VERSION_TAG) && !defined(QT_NO_VERSION_TAGGING)
121# ifndef QT_VERSION_TAG_SECTION
122# define QT_VERSION_TAG_SECTION __attribute__((section(".qtversion")))
123# endif
124# define QT_MANGLED_VERSION_TAG_IMPORT QT_VERSION_TAG_SYMBOL(QT_MANGLE_IMPORT_PREFIX, QT_MANGLE_NAMESPACE(qt_version_tag), QT_VERSION_MAJOR, QT_VERSION_MINOR)
125# define QT_MANGLED_VERSION_TAG QT_VERSION_TAG_SYMBOL(, QT_MANGLE_NAMESPACE(qt_version_tag), QT_VERSION_MAJOR, QT_VERSION_MINOR)
126
127QT_VERSION_TAG(QT_MANGLED_VERSION_TAG, QT_MANGLED_VERSION_TAG_IMPORT);
128
129# undef QT_MANGLED_VERSION_TAG
130# undef QT_MANGLED_VERSION_TAG_IMPORT
131# undef QT_VERSION_TAG_SECTION
132#endif
133
134QT_END_NAMESPACE
135
136#endif // QVERSIONTAGGING_H
137

source code of qtbase/src/corelib/global/qversiontagging.h