pe格式从入门到图形化显示（五）-RVA和FOA

前言

通过分析和解析Windows PE格式，并使用qt进行图形化显示

一、什么是Windows PE格式中的RVA和FOA？

PE文件格式的RVA（相对虚拟地址）和FOA（文件偏移地址）是用于描述文件在内存和磁盘中的位置的概念。

RVA是相对于PE文件载入地址的偏移位置，它是一个相对的地址（偏移）。当PE文件在磁盘中时，某个数据位置相对于文件头的偏移量称为文件偏移地址（FOA）。

RVA在程序加载到内存时被使用，它指向程序在内存中的虚拟地址。FOA在程序未加载到内存时被使用，它指向程序在磁盘上的文件偏移量。

二、RVA和FOA互相转换

1.转换数据结构体

struct RVA2FOAInfo
{
    QString sectionName;
    DWORD FOA = 0;
    DWORD VA = 0;
    DWORD RVA = 0;
};

2.RVA转FOA

RVA2FOAInfo PEParser::RVA2FOA(DWORD rva)
{
    RVA2FOAInfo info;
    //如果内存对齐大小等于文件对齐大小，FOA==RVA
    if (m_sectionAlignment == m_fileAlignment)
    {
        info.VA = m_imageBase + rva;
        info.RVA = info.FOA = rva;
        return info;
    }
    //如果RVA在PE头部，FOA==RVA
    DWORD headerSize = sizeof(IMAGE_DOS_HEADER) + sizeof(DWORD) + sizeof(IMAGE_FILE_HEADER);
    if (m_x86Flag)
    {
        headerSize += sizeof(IMAGE_OPTIONAL_HEADER32);
    }
    else
    {
        headerSize += sizeof(IMAGE_OPTIONAL_HEADER64);
    }
    headerSize += sizeof(IMAGE_SECTION_HEADER) * m_fileHeader.NumberOfSections;
    if (rva <= headerSize)
    {
        info.VA = m_imageBase + rva;
        info.RVA = info.FOA = rva;
        return info;
    }
    for (int i = 0; i < m_sections.size(); ++i)
    {
        //判断RVA处在哪个节中
        if (rva >= m_sections[i].VirtualAddress && rva < (m_sections[i].VirtualAddress + m_sections[i].SizeOfRawData))
        {
            info.VA = m_imageBase + rva;
            info.RVA = rva;
            info.FOA = rva - m_sections[i].VirtualAddress + m_sections[i].PointerToRawData;
            info.sectionName = QString::asprintf("%s", m_sections[i].Name);
        }
    }
    return info;
}

3.FOA转RVA

RVA2FOAInfo PEParser::FOA2RVA(DWORD foa)
{
    RVA2FOAInfo info;
    //如果内存对齐大小等于文件对齐大小，FOA==RVA
    if (m_sectionAlignment == m_fileAlignment)
    {
        info.VA = m_imageBase + foa;
        info.RVA = info.FOA = foa;
        return info;
    }
    //如果RVA在PE头部，FOA==RVA
    DWORD headerSize = sizeof(IMAGE_DOS_HEADER) + sizeof(DWORD) + sizeof(IMAGE_FILE_HEADER);
    if (m_x86Flag)
    {
        headerSize += sizeof(IMAGE_OPTIONAL_HEADER32);
    }
    else
    {
        headerSize += sizeof(IMAGE_OPTIONAL_HEADER64);
    }
    headerSize += sizeof(IMAGE_SECTION_HEADER) * m_fileHeader.NumberOfSections;
    if (foa <= headerSize)
    {
        info.VA = m_imageBase + foa;
        info.RVA = info.FOA = foa;
        return info;
    }
    for (int i = 0; i < m_sections.size(); ++i)
    {
        //判断FOA处在哪个节中
        if (foa >= m_sections[i].PointerToRawData && foa < (m_sections[i].PointerToRawData + m_sections[i].SizeOfRawData))
        {
            info.RVA = foa - m_sections[i].PointerToRawData + m_sections[i].VirtualAddress;
            info.VA = m_imageBase + info.RVA;
            info.FOA = foa;
            info.sectionName = QString::asprintf("%s", m_sections[i].Name);
        }
    }
    return info;
}