StackOverflow2013

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POQt, GCC, SSE and stack alignment
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copied!<p>I'm trying to make a program compiled with GCC and using Qt and SSE intrinsics. It seems that when one of my functions is called by Qt, the stack alignment is not preserved. Here's a short example to illustrate what I mean :</p> <pre><code>#include <cstdio> #include <emmintrin.h> #include <QtGui/QApplication.h> #include <QtGui/QWidget.h> class Widget: public QWidget { public: void paintEvent(QPaintEvent *) { __m128 a; printf("a: 0x%08x\n", ((void *) &a)); } }; int main(int argc, char** argv) { QApplication application(argc, argv); Widget w; w.paintEvent(NULL); // Called from here, my function behaves correctly w.show(); w.update(); // Qt will call Widget::paintEvent and my __m128 will not be // aligned on 16 bytes as it should application.processEvents(); return 0; } </code></pre> <p>Here's the output:</p> <pre><code>a: 0x0023ff40 // OK, that's aligned on 16 bytes a: 0x0023d14c // Not aligned! </code></pre> <p>Configuration:</p> <ul> <li>Intel Core2</li> <li>WinXP, SP3</li> <li>GCC 4.4 (Mingw included in the Qt SDK 2010.01)</li> </ul> <p>I tried to compile the example program with the same options as those I saw in the Qt makefile :</p> <pre><code>-O2 -Wall -frtti -fexceptions -mthreads </code></pre> <p>,link options:</p> <pre><code>-enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc -Wl,-s -mthreads </code></pre> <p>Now I don't know in which directions to search. Any hints would be appreciated. Thanks!</p> <p>Fabien</p>

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