Auto-detect whether 64-bit std::atomic really works

The C++ standard says it must, but some badly-configured toolchains seem
to be lacking support.

In particular, for some 32-bit platforms without native support for
them, GCC implements 64-bit atomics via out-of-line functions in
libatomic. If that library is missing... well, then std::atomic 64-bit
doesn't work and we mustn't try to use it.

This was found when trying to compile Qt 5.6 for MIPS 32-bit:

Linking library libQt5Core.so.5.6.0
.obj/qsimd.o: In function `std::__atomic_base<unsigned long long>::load(std::memory_order) const':
/opt/poky/1.7/sysroots/mips32r2-poky-linux/usr/include/c++/4.9.1/bits/atomic_base.h:500: undefined reference to `__atomic_load_8'
.obj/qsimd.o: In function `std::__atomic_base<unsigned long long>::store(unsigned long long, std::memory_order)':
/opt/poky/1.7/sysroots/mips32r2-poky-linux/usr/include/c++/4.9.1/bits/atomic_base.h:478: undefined reference to `__atomic_store_8'

Yocto bug report: https://bugzilla.yoctoproject.org/show_bug.cgi?id=8274

Change-Id: I42e7ef1a481840699a8dffff140224d6614e5c36
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 3d7586b760550b7d89594c8d7462fc30b868ecc6)
Reviewed-by: Dmitry Shachnev <mitya57@gmail.com>

1 files changed, 16 insertions, 1 deletions

diff --git a/tools/configure/configureapp.cpp b/tools/configure/configureapp.cpp
index 3bf0546ac1..5df8f7d645 100644
--- a/tools/configure/configureapp.cpp
+++ b/tools/configure/configureapp.cpp
@@ -1,7 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2015 The Qt Company Ltd.
-** Copyright (C) 2014 Intel Corporation
+** Copyright (C) 2015 Intel Corporation
 ** Contact: http://www.qt.io/licensing/
 **
 ** This file is part of the tools applications of the Qt Toolkit.
@@ -192,6 +192,7 @@ Configure::Configure(int& argc, char** argv)
     dictionary[ "SYSTEM_PROXIES" ]  = "no";
     dictionary[ "WERROR" ]          = "auto";
     dictionary[ "QREAL" ]           = "double";
+    dictionary[ "ATOMIC64" ]        = "auto";
 
     //Only used when cross compiling.
     dictionary[ "QT_INSTALL_SETTINGS" ] = "/etc/xdg";
@@ -2195,6 +2196,12 @@ bool Configure::checkAvailability(const QString &part)
     else if (part == "OBJCOPY")
         available = tryCompileProject("unix/objcopy");
 
+    else if (part == "ATOMIC64")
+        available = tryCompileProject("common/atomic64");
+
+    else if (part == "ATOMIC64-LIBATOMIC")
+        available = tryCompileProject("common/atomic64", "LIBS+=-latomic");
+
     else if (part == "ZLIB")
         available = findFile("zlib.h");
 
@@ -2343,6 +2350,10 @@ void Configure::autoDetection()
             dictionary["C++11"] = tryCompileProject("common/c++11") ? "yes" : "no";
     }
 
+    if (dictionary["ATOMIC64"] == "auto")
+        dictionary["ATOMIC64"] = checkAvailability("ATOMIC64") ? "yes" :
+                                 checkAvailability("ATOMIC64-LIBATOMIC") ? "libatomic" : "no";
+
     // Style detection
     if (dictionary["STYLE_WINDOWSXP"] == "auto")
         dictionary["STYLE_WINDOWSXP"] = checkAvailability("STYLE_WINDOWSXP") ? defaultTo("STYLE_WINDOWSXP") : "no";
@@ -2862,6 +2873,9 @@ void Configure::generateOutputVars()
         }
     }
 
+    if (dictionary["ATOMIC64"] == "libatomic")
+        qmakeConfig += "atomic64-libatomic";
+
     if (dictionary[ "ACCESSIBILITY" ] == "yes")
         qtConfig += "accessibility";
 
@@ -3661,6 +3675,7 @@ void Configure::generateConfigfiles()
         if (dictionary["QT_GLIB"] == "no")           qconfigList += "QT_NO_GLIB";
         if (dictionary["QT_INOTIFY"] == "no")        qconfigList += "QT_NO_INOTIFY";
         if (dictionary["QT_EVENTFD"] ==  "no")       qconfigList += "QT_NO_EVENTFD";
+        if (dictionary["ATOMIC64"] == "no")          qconfigList += "QT_NO_STD_ATOMIC64";
 
         if (dictionary["REDUCE_EXPORTS"] == "yes")     qconfigList += "QT_VISIBILITY_AVAILABLE";
         if (dictionary["REDUCE_RELOCATIONS"] == "yes") qconfigList += "QT_REDUCE_RELOCATIONS";