为什么在Webkit运行时pow()计算错误?

时间:2014-07-17 06:02:34

标签: c++ qt webkit pow x87

我有一个Qt C ++应用程序,其中有一个GUI线程,其中发生了一些浮点计算。它还会打开QWebView,其中有一个带有一些视频的Flash播放器。

很明显,关闭QWebView会干扰新的下一个浮点运算。 所以pow(double, double)会返回明确但不正确的值。

在一个案例中,它返回的值比正确值多1000倍。另一次与参数#inf一起使用时返回1. pow(10.0, 2.0)

我必须提到它是在不同的计算机上测试的,并不是特定于特定的CPU。

您是否有任何关于如何在Webkit中找到协处理器出错的地方以及如何防止它的建议?

样本(仅限x64)

环境:Qt 4.7.4,C ++,HTML和流程图

cpp

wrongpow::wrongpow(QWidget *parent, Qt::WFlags flags)
: QMainWindow(parent, flags)
{
 QVBoxLayout* layout = new QVBoxLayout(0);  
 m_view = new QWebView(this);  
 m_view->setMinimumSize(400, 400);
 m_view->settings()->setAttribute(QWebSettings::PluginsEnabled, true);
 m_view->settings()->setAttribute(QWebSettings::LocalContentCanAccessRemoteUrls, true);
 layout->addWidget(m_view);
 QDir dir(QApplication::applicationDirPath());
 dir.cd("media");
 m_view->load(QUrl(QFileInfo(dir, "index.html").absoluteFilePath()));

 QPushButton* button = new QPushButton(QLatin1String("Click on video start"), this);
 layout->addWidget(button);
 Q_ASSERT(connect(button, SIGNAL(clicked()), this, SLOT(closeView()))); 

 setLayout(layout);
 adjustSize();
}  
Q_SLOT void wrongpow::closeView()
{
 delete m_view;
 m_view = NULL;

 double wrongResult = pow(10.0, 2.0);
 Q_ASSERT(wrongResult == 100.0);
}

html

<div id='player' style='width:100%; height:100%;'>
    <object width='100%' height='100%' id='_494187117' name='_494187117' data='js/plugins/flowplayer-3.2.18.swf' type='application/x-shockwave-flash'>                      
        <param name='wmode' value='opaque'>         
        <param name='flashvars' value='config={&quot;clip&quot;:{&quot;url&quot;:&quot;mp4:vod/demo.flowplayer/buffalo_soldiers.mp4&quot;,&quot;scaling&quot;:&quot;fit&quot;,&quot;provider&quot;:&quot;hddn&quot;,&quot;live&quot;:true},&quot;plugins&quot;:{&quot;hddn&quot;:{&quot;url&quot;:&quot;js/plugins/flowplayer.rtmp-3.2.13.swf&quot;,&quot;netConnectionUrl&quot;:&quot;rtmp://r.demo.flowplayer.netdna-cdn.com/play&quot;}},&quot;canvas&quot;:{&quot;backgroundGradient&quot;:&quot;none&quot;}}'>
    </object>
</div>  

这是一个包含来源的完整工作程序: Download 15MB

3 个答案:

答案 0 :(得分:6)

pow的错误结果的原因是x87寄存器ST0-ST3变为1#SNAN,因此TAGS = 0xFF。它发生在包含视频flash对象的QWebView的破坏期间。 x87和SSE的控制字包含正确的值。 经过测试的Adove Flash库:NPSWF64_14_0_0_125.dll

WebCore::PluginView::stop方法调用Adobe Flash插件对象的析构函数时会发生这种情况。

NPError npErr = m_plugin->pluginFuncs()->destroy(m_instance, &savedData);

以下是破坏寄存器的程序(NPSWF64.dll)(实际上它使用与x87寄存器相关的MMX寄存器):

mov         qword ptr [rsp+8],rcx 
mov         qword ptr [rsp+10h],rdx 
mov         qword ptr [rsp+18h],r8 
push        rsi  
push        rdi  
push        rbx  
mov         rdi,qword ptr [rsp+20h] 
mov         rsi,qword ptr [rsp+28h] 
mov         rcx,qword ptr [rsp+30h] 
cmp         rcx,20h 
jle         000000002F9D8A2D 
sub         rcx,20h 

// writes wrong values to the registers:
movq        mm0,mmword ptr [rsi] 
movq        mm1,mmword ptr [rsi+8] 
movq        mm2,mmword ptr [rsi+10h] 
movq        mm3,mmword ptr [rsi+18h] 

add         rsi,20h 
movq        mmword ptr [rdi],mm0
movq        mmword ptr [rdi+8],mm1 
movq        mmword ptr [rdi+10h],mm2 
movq        mmword ptr [rdi+18h],mm3 
add         rdi,20h 
sub         rcx,20h 
jge         000000002F9D89F1 
add         rcx,20h 
rep movs    byte ptr [rdi],byte ptr [rsi] 
pop         rbx  
pop         rdi  
pop         rsi  
ret         

为防止由此错误导致的pow错误计算,需要恢复寄存器值。我用最简单的方法来做到这一点。当插件被销毁时,我用一些参数调用pow并恢复寄存器。下一个电话会是正确的 通过使用float.h库中的方法将新值写入寄存器,有一种更复杂(但可能是正确的)方法。

答案 1 :(得分:2)

只是稍微补充一下,我想我遇到了同样的问题(在64位C#应用程序中调用Math.Cos,并且恰好在.NET Windows窗体WebBrowser控件中显示Flash视频)。

同样,在我的情况下,似乎64位Flash OCX(16.0.0.305)中的以下代码在MM0,MM1,MM2,MM3寄存器中留下了无效值(此代码似乎是某种快速的记忆副本):

C:\Windows\System32\Macromed\Flash\Flash64_16_0_0_305.ocx
00000000`2f9833c0 48894c2408      mov     qword ptr [rsp+8],rcx
00000000`2f9833c5 4889542410      mov     qword ptr [rsp+10h],rdx
00000000`2f9833ca 4c89442418      mov     qword ptr [rsp+18h],r8
00000000`2f9833cf 56              push    rsi
00000000`2f9833d0 57              push    rdi
00000000`2f9833d1 53              push    rbx
00000000`2f9833d2 488b7c2420      mov     rdi,qword ptr [rsp+20h]
00000000`2f9833d7 488b742428      mov     rsi,qword ptr [rsp+28h]
00000000`2f9833dc 488b4c2430      mov     rcx,qword ptr [rsp+30h]
00000000`2f9833e1 4881f920000000  cmp     rcx,20h
00000000`2f9833e8 7e43            jle     Flash64_16_0_0_305!DllUnregisterServer+0x3c2a2d (00000000`2f98342d)
00000000`2f9833ea 4881e920000000  sub     rcx,20h
00000000`2f9833f1 0f6f06          movq    mm0,mmword ptr [rsi]
00000000`2f9833f4 0f6f4e08        movq    mm1,mmword ptr [rsi+8]
00000000`2f9833f8 0f6f5610        movq    mm2,mmword ptr [rsi+10h]
00000000`2f9833fc 0f6f5e18        movq    mm3,mmword ptr [rsi+18h]
00000000`2f983400 4881c620000000  add     rsi,20h
00000000`2f983407 0f7f07          movq    mmword ptr [rdi],mm0
00000000`2f98340a 0f7f4f08        movq    mmword ptr [rdi+8],mm1
00000000`2f98340e 0f7f5710        movq    mmword ptr [rdi+10h],mm2
00000000`2f983412 0f7f5f18        movq    mmword ptr [rdi+18h],mm3
00000000`2f983416 4881c720000000  add     rdi,20h
00000000`2f98341d 4881e920000000  sub     rcx,20h
00000000`2f983424 7dcb            jge     Flash64_16_0_0_305!DllUnregisterServer+0x3c29f1 (00000000`2f9833f1)
00000000`2f983426 4881c120000000  add     rcx,20h
00000000`2f98342d f3a4            rep movs byte ptr [rdi],byte ptr [rsi]
00000000`2f98342f 5b              pop     rbx
00000000`2f983430 5f              pop     rdi
00000000`2f983431 5e              pop     rsi
00000000`2f983432 c3              ret

Flash OCX中的上述代码是在Web浏览器离开显示Flash视频的页面时执行的。

在此代码执行之前,浮点寄存器如下(使用WinDbg.exe检查):

fpcw=027f fpsw=3820 fptw=0080
st0= 6.00000000000000000000000...0e+0001 (0:4004:f000000000000000)
st1= 0.00000000000000000000000...0e+0000 (0:0000:0000000000000000)
st2= 0.00000000000000000000000...0e+0000 (0:0000:0000000000000000)
st3= 0.00000000000000000000000...0e+0000 (0:0000:0000000000000000)
st4= 0.00000000000000000000000...0e+0000 (0:0000:0000000000000000)
st5= 1.00000000000000000000000...0e+0000 (0:3fff:8000000000000000)
st6= 8.94231504669236176852000...0e-0001 (0:3ffe:e4ec5b1b9b742000)
st7= 0.00000000000000000000000...0e+0000 (0:0000:0000000000000000)
mxcsr=00001fa4

执行上述代码后,浮点寄存器如下:

fpcw=027f fpsw=0020 fptw=00ff
st0=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st1=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st2=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st3=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st4= 1.00000000000000000000000...0e+0000 (0:3fff:8000000000000000)
st5= 8.94231504669236176852000...0e-0001 (0:3ffe:e4ec5b1b9b742000)
st6= 0.00000000000000000000000...0e+0000 (0:0000:0000000000000000)
st7= 6.00000000000000000000000...0e+0001 (0:4004:f000000000000000)
mxcsr=00001fa4

此时浮点寄存器似乎处于“损坏”状态。

所以稍后,回到C#程序,当执行Math.Cos时,fld操作码失败,因为它试图将值2.0推送到浮点堆栈上(即,当它试图准备计算2.0的余弦时):

COMDouble::Cos:
000007FE`E1D01570  movsd   mmword ptr [rsp+8],xmm0
000007FE`E1D01576  fld     qword ptr [rsp+8]
000007FE`E1D0157A  fcos
000007FE`E1D0157C  fstp    qword ptr [rsp+8]
000007FE`E1D01580  movsd   xmm0,mmword ptr [rsp+8]
000007FE`E1D01586  ret

在执行fld操作码之前,浮点寄存器与Flash OCX完全一样(即如上所述):

fpcw=027f fpsw=0020 fptw=00ff
st0=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st1=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st2=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st3=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st4= 1.00000000000000000000000...0e+0000 (0:3fff:8000000000000000)
st5= 8.94231504669236176852000...0e-0001 (0:3ffe:e4ec5b1b9b742000)
st6= 0.00000000000000000000000...0e+0000 (0:0000:0000000000000000)
st7= 6.00000000000000000000000...0e+0001 (0:4004:f000000000000000)
mxcsr=00001fa4

执行fld操作码后,浮点寄存器立即如下(注意st0是#IND而不是预期值2.00000000000000000000000 ... 0e + 0000):

fpcw=027f fpsw=3a61 fptw=00ff
st0=-1.#IND0000000000000000000...0e+0000 (1:7fff:c000000000000000)
st1=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st2=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st3=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st4=-1.#SNAN000000000000000000...0e+0000 (1:7fff:0000000000000000)
st5= 1.00000000000000000000000...0e+0000 (0:3fff:8000000000000000)
st6= 8.94231504669236176852000...0e-0001 (0:3ffe:e4ec5b1b9b742000)
st7= 0.00000000000000000000000...0e+0000 (0:0000:0000000000000000)
mxcsr=00001fa4

这意味着fcos操作码尝试计算#IND的余弦值。因此,最终C#中Math.Cos的返回值为Double.NaN而不是预期的-0.416146836547142。

解析上面的浮点状态字(FPSW)值0x3a61表示问题是“尝试将值加载到非空闲的寄存器中”:

3a61: 0011 1010 0110 0001

    TOP (13,12,11):          111
    C3,C2,C1,C0 (14,10,9,8): 0 010  (ie. C1 is 1)  <-- loading a value into a register which is not free
    IR (7):                  0  Interrupt Request
    SF (6):                  1  Stack Fault  <-- loading a value into a register which is not free
    P (5):                   1  Precision
    U (4):                   0  Underflow
    O (3):                   0  Overflow
    Z (2):                   0  Zero Divide
    D (1):                   0  Denormalised
    I (0):                   1  Invalid Operation

请注意,问题只会在第一次尝试Math.Cos(2)时发生(即导航离开Flash视频页面后不久)。第二次和以后的计算Math.Cos(2)的尝试都成功了。

如果在播放(或暂停)Flash视频时处理WebBrowser控件,也会出现此问题。

所以一些潜在的解决方法是:

  1. 执行一次虚拟数学计算并忽略结果。

  2. 写一个64位DLL,它导出一个执行finit或emms操作码的函数(以重置浮点寄存器的状态)。从C#调用该函数。

  3. 以32位进程运行。

  4. 注意:在C#中抛出一个虚拟异常然后捕获该异常没有帮助(建议其他浮点损坏问题)。

    以下是一些重现问题的C#代码(确保编译并运行为64位;在视频开始播放后单击“计算”按钮)。

    using System;
    using System.IO;
    using System.Windows.Forms;
    
    namespace FlashTest
    {
        public partial class TestForm : Form
        {
            public TestForm()
            {
                // Windows 7 SP1 64 bit
                // Internet Explorer 11 (11.0.9600.17633)
                // Flash Player 16.0.0.305
                // Visual Studio 2013 (12.0.31101.00)
                // .NET 4.5 (4.0.30319.34209)
    
                InitializeComponent();
                addressTextBox.Text = "http://www.youtube.com/v/JVGdyC9CvFQ?autoplay=1";
                GoButtonClickHandler(this, EventArgs.Empty);
            }
    
            private void GoButtonClickHandler(object sender, EventArgs e)
            {
                string path = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName() + ".html");
                File.WriteAllText(path, string.Format(@"<html><body>
                    <object classid=""clsid:D27CDB6E-AE6D-11CF-96B8-444553540000"" width=""100%"" height=""100%"" id=""youtubeviewer"">
                        <param name=""movie"" value=""{0}"">
                    </object></body></html>", addressTextBox.Text));
                webBrowser.Navigate(path);
            }
    
            private void CalculateButtonClickHandler(object sender, EventArgs e)
            {
                webBrowser.DocumentCompleted += DocumentCompletedHandler;
                webBrowser.Navigate("about:blank");
            }
    
            private void DocumentCompletedHandler(object sender, WebBrowserDocumentCompletedEventArgs e)
            {
                webBrowser.DocumentCompleted -= DocumentCompletedHandler;
                MessageBox.Show("Math.Cos(2) returned " + Math.Cos(2));
            }
        }
    }
    
    namespace FlashTest
    {
        partial class TestForm
        {
            /// <summary>
            /// Required designer variable.
            /// </summary>
            private System.ComponentModel.IContainer components = null;
    
            /// <summary>
            /// Clean up any resources being used.
            /// </summary>
            /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
            protected override void Dispose(bool disposing)
            {
                if (disposing && (components != null))
                {
                    components.Dispose();
                }
                base.Dispose(disposing);
            }
    
            #region Windows Form Designer generated code
    
            /// <summary>
            /// Required method for Designer support - do not modify
            /// the contents of this method with the code editor.
            /// </summary>
            private void InitializeComponent()
            {
                this.webBrowser = new System.Windows.Forms.WebBrowser();
                this.addressTextBox = new System.Windows.Forms.TextBox();
                this.goButton = new System.Windows.Forms.Button();
                this.calculateButton = new System.Windows.Forms.Button();
                this.SuspendLayout();
                // 
                // webBrowser
                // 
                this.webBrowser.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom) 
                | System.Windows.Forms.AnchorStyles.Left) 
                | System.Windows.Forms.AnchorStyles.Right)));
                this.webBrowser.Location = new System.Drawing.Point(12, 41);
                this.webBrowser.MinimumSize = new System.Drawing.Size(20, 20);
                this.webBrowser.Name = "webBrowser";
                this.webBrowser.Size = new System.Drawing.Size(560, 309);
                this.webBrowser.TabIndex = 3;
                // 
                // addressTextBox
                // 
                this.addressTextBox.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left) 
                | System.Windows.Forms.AnchorStyles.Right)));
                this.addressTextBox.Location = new System.Drawing.Point(12, 14);
                this.addressTextBox.Name = "addressTextBox";
                this.addressTextBox.Size = new System.Drawing.Size(398, 20);
                this.addressTextBox.TabIndex = 0;
                // 
                // goButton
                // 
                this.goButton.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Right)));
                this.goButton.Location = new System.Drawing.Point(416, 12);
                this.goButton.Name = "goButton";
                this.goButton.Size = new System.Drawing.Size(75, 23);
                this.goButton.TabIndex = 1;
                this.goButton.Text = "&Go";
                this.goButton.UseVisualStyleBackColor = true;
                this.goButton.Click += new System.EventHandler(this.GoButtonClickHandler);
                // 
                // calculateButton
                // 
                this.calculateButton.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Right)));
                this.calculateButton.Location = new System.Drawing.Point(497, 12);
                this.calculateButton.Name = "calculateButton";
                this.calculateButton.Size = new System.Drawing.Size(75, 23);
                this.calculateButton.TabIndex = 2;
                this.calculateButton.Text = "&Calculate";
                this.calculateButton.UseVisualStyleBackColor = true;
                this.calculateButton.Click += new System.EventHandler(this.CalculateButtonClickHandler);
                // 
                // TestForm
                // 
                this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
                this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
                this.ClientSize = new System.Drawing.Size(584, 362);
                this.Controls.Add(this.webBrowser);
                this.Controls.Add(this.goButton);
                this.Controls.Add(this.addressTextBox);
                this.Controls.Add(this.calculateButton);
                this.Name = "TestForm";
                this.Text = "Adobe Flash Test";
                this.ResumeLayout(false);
                this.PerformLayout();
    
            }
    
            #endregion
    
            private System.Windows.Forms.WebBrowser webBrowser;
            private System.Windows.Forms.TextBox addressTextBox;
            private System.Windows.Forms.Button goButton;
            private System.Windows.Forms.Button calculateButton;
        }
    }
    

答案 2 :(得分:1)

显然你遇到了Qt的webkit版本中的错误。我无法在QT 5.3中使用QVCreator版本在版本和调试中使用MSVC 13 x64进行重现。

QtWebKit已经报告了浮点数的一些错误: