Ported to 2005 - Strange variable alignment causing issues

=?Utf-8?B?VHVyc2k=?= <msdnlion@yiffco.com>
Sat, 10 Jun 2006 02:30:02 -0700
Gonna try here as a starting point. I'm migrating an old Visual C++ 6 project
to VC++ 2005. Just one class is misbehaving - it's member variables are
located at odd addresses (literally, and not aligned to a 4 byte multiple),
and when the code attempts to access them, it typically reads and writes to
the wrong location (it accesses properly aligned addresses), leading to
corruption of the data and stack.

This is with the code copied straight across, and with the code updated so
all the string warnings are updated. If I compile *just* the affected file
(right-click on the file and select 'compile'), then the members are dword
aligned and all is well. However, if I build the entire project, then then
members are NOT aligned and it's not so well.

I have not been able to reproduce in a sample app, and sadly, my application
is pretty large. However, I'd be willing to provide the code to MS for
debugging help.

The class in question is a property page dialog. My class declaration looks
like this:

class DlgWWW : public CPropertyPage

// Construction
    void UpdateList();
    CString FileList;
    void UpdateOutText();
    CString myIP;
    bool fRoutable;

// Dialog Data
    enum { IDD = IDD_CFG_WWW };
    CListBox m_List;
    CEdit m_URLText;
    BOOL m_EnableWWW;
    int m_WWWPort;
    int m_MaxConn;
    int m_MaxFileSize;
    int m_WWWTimeout;
    BOOL m_WWWLogEnable;
    char szWWWLogPath[1024];

// Overrides
    // ClassWizard generate virtual function overrides
    virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support

// Implementation
    // Generated message map functions
    virtual BOOL OnInitDialog();
    afx_msg void OnWwwon();
    afx_msg void OnNewfile();
    afx_msg void OnRemovefile();
    afx_msg void OnSetdefault();
    afx_msg void OnSelchangeList1();
    afx_msg void OnKillfocusWwwport();
    afx_msg void OnLogbrowse();


I'm checking the variables right in the constructor, which is where they get

DlgWWW::DlgWWW() : CPropertyPage(DlgWWW::IDD)
    if (theApp.WWWPort == 0) {

    m_EnableWWW = theApp.EnableWWW;
    m_WWWPort = theApp.WWWPort;
    m_MaxConn = theApp.WWWMaxConn;
    m_MaxFileSize = theApp.MaxFileSize;
    m_WWWTimeout = theApp.WWWTimeout;
    m_WWWLogEnable = theApp.WWWLogEnable;
.... (etc, it's already broken by this point).

I have addresses like 0x0012dbb5 for m_EnableWWW (int). When the code
actually runs the assignment above, it actually writes to 0x0012dbb8. The
assembly looks like this:

    m_EnableWWW = theApp.EnableWWW;
0046B93E movzx eax,byte ptr [theApp+2A1h (69D351h)]
0046B945 mov ecx,dword ptr [ebp-14h]
0046B948 mov dword ptr [ecx+13Ch],eax
    m_WWWPort = theApp.WWWPort;
0046B94E mov eax,dword ptr [ebp-14h]
0046B951 mov ecx,dword ptr [theApp+264h (69D314h)]
0046B957 mov dword ptr [eax+140h],ecx

This *seems* to be the only file affected, but I'm not certain yet. It
definately seems wrong that the members should live at such odd offsets, but
maybe I'm missing something? I don't think there are any #pragma pack active
and the settings are the default as migrated:

Compiler: /Od /D "WIN32" /D "_DEBUG" /D "_WINDOWS" /D "_VC80_UPGRADE=0x0600"
/D "_MBCS" /Gm /EHsc /RTC1 /MTd /Fp".\Debug/SCWebCam2.pch" /Fo".\Debug/"
/Fd".\Debug/" /FR".\Debug\\" /W3 /nologo /c /ZI /TP /errorReport:prompt

/DELAYLOAD:"OleAcc.dll" /DEBUG /PDB:".\Debug/SCWebCam3.pdb"
jpglibDMTS.lib libpngdmts.lib zlibdmts.lib vfw32.lib rasapi32.lib DelayImp.lib

I'd really like to move up to the new system, any ideas what to look at?

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