Question

我需要使用GetVolumeInformationW。由于原因未知，我决定动态加载Kernel32.dll，在运行时解析函数地址...结果是内存损坏问题和修改堆栈的一些奇怪的副作用。虽然静态版本就像一个魅力，我可以坚持下去并继续前进，我想调查此事。

源代码是自我解释的（如果您需要更多信息请注释，可以找到完整版here）：

#include <QtDebug>
#include <QByteArray>
#include <QLibrary>
#include <QDir>

static inline QString LAT1(const char *str, const int len = -1) {
    return QString::fromLatin1(str, len);
}

template <typename T>
static inline QByteArray createByteArray(const T *from, const int numElements) {
    return QByteArray(reinterpret_cast<const char*>(from), sizeof(T) * numElements);
}

// This one resolves functions from Kernel32.dll dynamically and uses standard types.
// (Dynamic linking.)
QByteArray fingerprintDynamic() {
    const uint32_t kMaxPath = 260 + 1;  // MAX_PATH + 1
    wchar_t path[kMaxPath]       = {0};
    wchar_t name[kMaxPath]       = {0};
    wchar_t fileSystem[kMaxPath] = {0};
    uint32_t serial = 0;
    uint32_t maximumComponentLength = 0;
    uint32_t fileSystemFlags = 0;

    QLibrary kernel32("kernel32");
    typedef uint32_t (*fnGetLastError)(void);
    typedef bool (*fnGetVolumeInformationW)(const wchar_t*, wchar_t*, uint32_t, uint32_t*, uint32_t*,
                                            uint32_t*, wchar_t*, uint32_t);
    fnGetVolumeInformationW GetVolumeInformationW = reinterpret_cast<fnGetVolumeInformationW>(kernel32.resolve("GetVolumeInformationW"));
    fnGetLastError GetLastError = reinterpret_cast<fnGetLastError>(kernel32.resolve("GetLastError"));

    if (!GetVolumeInformationW) {
        qWarning(LAT1("GetVolumeInformationW() not resolved: %1").arg(kernel32.errorString()).toLatin1().constData());
        return QByteArray();
    }
    else if (!GetLastError) {
        qWarning(LAT1("GetLastError() not resolved: %1").arg(kernel32.errorString()).toLatin1().constData());
        return QByteArray();
    }

    QDir::toNativeSeparators(QDir::rootPath()).toWCharArray(path);
    bool apiCall = GetVolumeInformationW(path, name, kMaxPath, &serial, &maximumComponentLength,
                                         &fileSystemFlags, fileSystem, kMaxPath);
    if (!apiCall)
        qWarning(LAT1("GetVolumeInformationW() failed: %1").arg(GetLastError()).toLatin1().constData());

    // At this point, fileSystem is correct and contains
    // L"NTFS"

    // ONLY HAPPENS IN DEBUG MODE
    //
    // After this call memory becomes corrupted. wcslen() is not a problem.
    // And createByteArray<>() is ok too, I believe.
    //size_t len;  // But if I change stack a bit (like uncomment this line),
                   // result will be correct, so I guess it's related to memory offset.
    return createByteArray<wchar_t>(fileSystem, wcslen(fileSystem));
}

void print(const QByteArray &bytes) {
    qDebug() << QString::fromWCharArray(reinterpret_cast<const wchar_t*>(bytes.constData()));
    qDebug() << bytes.size() << "bytes" << bytes.toHex();
    qDebug() << "";
}

int main(int, char**)
{    
    qDebug() << "dynamic";
    print(fingerprintDynamic());

    return 0;
}

示例输出：

// this is DEBUG build
dynamic 
"(?(" 
8 bytes "280052f828000400"

// this is RELEASE build
// (same with `size_t len` uncommenented before `return` in DEBUG)
dynamic 
"NTFS" 
8 bytes "4e00540046005300"

问题是：这种行为的原因是什么？我的错误隐藏在哪里？

我正在使用g++.exe (GCC) 4.4.0，Qt 4.8.1和Creator 2.5.2。

Answer 1

问题可能是由于调用约定不匹配引起的。 GetVolumeInformationW()具有调用约定WINAPI，因此将函数指针类型更改为：

typedef BOOL (WINAPI *fnGetVolumeInformationW)(const wchar_t*,
                                               wchar_t*,
                                               uint32_t,
                                               uint32_t*,
                                               uint32_t*,
                                               uint32_t*,
                                               wchar_t*,
                                               uint32_t);

WINAPI正在调用约定__stdcall，而默认值为__cdecl。请注意，返回类型为BOOL，而不是bool。

调试模式下的内存损坏（？）

1 个答案: