From 3d7586b760550b7d89594c8d7462fc30b868ecc6 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Tue, 8 Sep 2015 20:35:33 -0300
Subject: 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>
---
 configure | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

(limited to 'configure')

diff --git a/configure b/configure
index 86571546fc..fcfe8b957f 100755
--- a/configure
+++ b/configure
@@ -2,7 +2,7 @@
 #############################################################################
 ##
 ## Copyright (C) 2015 The Qt Company Ltd.
-## Copyright (C) 2013 Intel Corporation.
+## Copyright (C) 2015 Intel Corporation.
 ## Contact: http://www.qt.io/licensing/
 ##
 ## This file is the build configuration utility of the Qt Toolkit.
@@ -662,6 +662,7 @@ CFG_SYSTEM_PROXIES=no
 CFG_ANDROID_STYLE_ASSETS=yes
 CFG_GSTREAMER=auto
 CFG_GSTREAMER_VERSION=""
+CFG_ATOMIC64=auto
 
 # Target architecture
 CFG_ARCH=
@@ -4389,6 +4390,15 @@ if compileTest common/c++default "default C++ standard edition"; then
     fi
 fi
 
+# Detect whether 64-bit std::atomic works -- some 32-bit platforms require extra library support
+if compileTest common/atomic64 "64-bit std::atomic"; then
+    CFG_ATOMIC64=yes
+elif compileTest common/atomic64 "64-bit std::atomic in -latomic" -latomic; then
+    CFG_ATOMIC64=libatomic
+else
+    CFG_ATOMIC64=no
+fi
+
 # detect sse2 support
 if [ "${CFG_SSE2}" = "auto" ]; then
     if compileTest common/sse2 "sse2"; then
@@ -6127,6 +6137,10 @@ if [ "$CFG_STDCXX" != "c++98" ]; then
     fi
 fi
 
+if [ "$CFG_ATOMIC64" = "libatomic" ]; then
+    QMAKE_CONFIG="$QMAKE_CONFIG atomic64-libatomic"
+fi
+
 if [ "$CFG_SILENT" = "yes" ]; then
     QMAKE_CONFIG="$QMAKE_CONFIG silent"
 fi
@@ -6681,6 +6695,10 @@ else
     echo "#define QT_POINTER_SIZE $?" >>"$outpath/src/corelib/global/qconfig.h.new"
 fi
 
+if [ "$CFG_ATOMIC64" = "no" ]; then
+    echo "#define QT_NO_STD_ATOMIC64" >> "$outpath/src/corelib/global/qconfig.h.new"
+fi
+
 #REDUCE_RELOCATIONS is a elf/unix only thing, so not in windows configure.exe
 if [ "$CFG_REDUCE_RELOCATIONS" = "yes" ]; then
     echo "#define QT_REDUCE_RELOCATIONS" >>"$outpath/src/corelib/global/qconfig.h.new"
-- 
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