From 4cc1f128c4b9894b94ffdd5d0a32257ead7a9cf5 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Martin=20Storsj=C3=B6?= Date: Fri, 24 Nov 2017 10:10:23 +0200 Subject: [PATCH 6/9] moc: Initialize staticMetaObject with the highest user-settable priority The referenced static meta object for the superclass might be in a different DLL. In this case, the whole QMetaObject can't be initialized all via preinitialized data in the data section of the binary, but must run code at runtime to fill in the value of the dllimported pointer. In these cases, both GCC and MSVC initialize as much as possible statically, while only filling in the dllimported values (QMetaObject::d::superdata) at runtime. Clang, on the other side, initializes the whole struct at runtime if some part of it needs runtime initialization, leaving the struct completely uninitialized before constructors are run. In C++, there are no guarantees for in what order constructors in different translation units are executed. This in particular means that there are no guarantees as to whether qRegisterWidgetsVariant() in qwidgetsvariants.cpp runs before or after the runtime initialization of QWidget::staticMetaObject. With GCC and MSVC, this doesn't seem to have mattered since only the superdata pointer of the staticMetaObject was uninitialized - everything else was initialized, and the superdata pointer doesn't seem to be accessed during qRegisterWidgetsVariant. With clang, the whole staticMetaObject is uninitialized, unless the staticMetaObject has been initialized before (and the initialization order is undefined). By setting a manual priority (which is a GCC extension that also clang supports) for the staticMetaObjects, we can be sure that these are initialized before the actual explicit constructor invocations (without any explicit initialization priority) that can access the staticMetaObjects. Change-Id: I64a82f12d690528567509791bae088b6304e189b Reviewed-by: Olivier Goffart (Woboq GmbH) Backport-Of: 74118a4784569046d5fdf5e08c99f8b1b43e9710 (v5.10.1) moc: Only use the init_priority attribute when targeting windows While both GCC and the GCC compatible clang support this attribute in general, GCC doesn't support it when targeting macOS, ending up with errors like these: error: 'init_priority' attribute is not supported on this platform This error isn't a property of the platform itself though, since clang supports the attribute just fine on macOS. The attribute is only used to work around an issue with dllimport on windows, so limit its use to that platform, to avoid issues with it potentially being unsupported on platforms other than macOS as well. This fixes compiling with GCC for macOS. Change-Id: I0235e6365635d73233951566c10ad869b26a0fc6 Reviewed-by: Thiago Macieira Backport-Of: b97765efd452921f75c1d04820c4b5e9e9d49100 (5.11 branch) --- src/corelib/global/qglobal.h | 6 ++++++ src/tools/moc/generator.cpp | 4 ++-- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/src/corelib/global/qglobal.h b/src/corelib/global/qglobal.h index 4528005177..3a3f8d40da 100644 --- a/src/corelib/global/qglobal.h +++ b/src/corelib/global/qglobal.h @@ -499,6 +499,12 @@ typedef qptrdiff qintptr; # define Q_ALWAYS_INLINE inline #endif +#if defined(Q_CC_GNU) && defined(Q_OS_WIN) +# define QT_INIT_METAOBJECT __attribute__((init_priority(101))) +#else +# define QT_INIT_METAOBJECT +#endif + //defines the type for the WNDPROC on windows //the alignment needs to be forced for sse2 to not crash with mingw #if defined(Q_OS_WIN) diff --git a/src/tools/moc/generator.cpp b/src/tools/moc/generator.cpp index 99629f0427..8cbeb4ce78 100644 --- a/src/tools/moc/generator.cpp +++ b/src/tools/moc/generator.cpp @@ -525,9 +525,9 @@ void Generator::generateCode() // Finally create and initialize the static meta object // if (isQt) - fprintf(out, "const QMetaObject QObject::staticQtMetaObject = {\n"); + fprintf(out, "QT_INIT_METAOBJECT const QMetaObject QObject::staticQtMetaObject = {\n"); else - fprintf(out, "const QMetaObject %s::staticMetaObject = {\n", cdef->qualified.constData()); + fprintf(out, "QT_INIT_METAOBJECT const QMetaObject %s::staticMetaObject = {\n", cdef->qualified.constData()); if (isQObject) fprintf(out, " { Q_NULLPTR, "); -- 2.14.3 (Apple Git-98)