Qt，GCC，SSE和堆栈对齐 [英] Qt, GCC, SSE and stack alignment

问题描述

我试图编写一个用GCC编译的程序，并使用Qt和SSE内在函数。
看来，当我的一个函数被Qt调用时，堆栈对齐不会被保留。这里有一个简短的例子来说明我的意思：

  #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 \\\
，（（void *）& a））; 
} 
}; 
 
 
 int main（int argc，char ** argv）
 {
 QApplication应用程序（argc，argv）; 
 Widget w; 
 w.paintEvent（NULL）; //从这里调用，我的函数行为正确
 w.show（）; 
 w.update（）; 
 // Qt将调用Widget :: paintEvent，并且我的__m128不会是
 //在16个字节上对齐，因为它应该是
 application.processEvents（）; 
 
返回0; 
} 
  

以下是输出：

  a：0x0023ff40 //确定，这对齐16个字节
a：0x0023d14c //未对齐！ 
  

配置：

• Intel Core2


• WinXP，SP3


• GCC 4.4（包含在Qt SDK 2010.01中的Mingw）
  

我尝试使用与我在Qt makefile中看到的选项相同的选项来编译示例程序：

  -O2 -Wall -frtti -fexceptions -mthreads 
  

，链接选项：

  -enable-stdcall-fixup -Wl，-enable-auto-import -Wl，-enable-runtime-pseudo- reloc -Wl，-s -mthreads 
  

现在我不知道要在哪个方向上搜索。
任何提示将不胜感激。谢谢！

Fabien

解决方案

您可以使用<$

-mstackrealign $ b $ c> -mstackrealign 可以在您的源代码中添加属性。 $ b在条目处重新对齐堆栈。在Intel x86上，-mstackrealign选项将生成备用序幕和尾声，以便在必要时重新对齐运行时堆栈。这支持将保留4字节对齐堆栈的传统代码与保留16字节堆栈以保持SSE兼容性的现代代码混合。另请参见属性force_align_arg_pointer，适用于各个功能。

（from GCC文档）

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 :

#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;
}

Here's the output:

a: 0x0023ff40 // OK, that's aligned on 16 bytes
a: 0x0023d14c // Not aligned!

Configuration:

• Intel Core2
• WinXP, SP3
• GCC 4.4 (Mingw included in the Qt SDK 2010.01)

I tried to compile the example program with the same options as those I saw in the Qt makefile :

-O2 -Wall -frtti -fexceptions -mthreads

,link options:

-enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc -Wl,-s -mthreads

Now I don't know in which directions to search. Any hints would be appreciated. Thanks!

Fabien

解决方案

You can use the option -mstackrealign to do that without adding attributes to your source code:

-mstackrealign Realign the stack at entry. On the Intel x86, the -mstackrealign option will generate an alternate prologue and epilogue that realigns the runtime stack if necessary. This supports mixing legacy codes that keep a 4-byte aligned stack with modern codes that keep a 16-byte stack for SSE compatibility. See also the attribute force_align_arg_pointer, applicable to individual functions.

(from the GCC docs)

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