c++ - 以编程方式从函数名中获取序数

Question

给定它的名称，在 C++ 中获取导出的 dll 函数的序数的最简单方法是什么？（寻找一种不涉及自己解析 IAT 的方法......）

Answer 1

我想不出任何非常简单的方法来做你想做的事。你至少有几个我可以看到的选项：

1. 采取马克给出的路线，虽然它看起来有点笨拙并且可能有一些缺点。
2. 使用名称指针表 (NPT) 和导出序号表 (EOT) 查找导出序号。

我看到第一个选项的主要问题是您不知道要尝试多少个序数（序数中可能存在间隙，因此指望GetProcAddress返回 NULL 来表示结束是行不通的）。它也有些低效，因为它需要重复进行大量Win32 调用，并且基本上相当于对导出地址表的线性搜索。确实很不雅。

作为替代方案，您可以搜索 NPT 并使用 EOT 中的结果索引来获取序数。这是一种更优雅的方法，因为它以最直接的方式到达序数（实际上与动态链接器用于将导出名称解析为其地址的方法相同）。此外，由于 NPT 是按词法排序的，因此可以进行二进制搜索，这显然比其他方法的线性搜索更可取。实际上，使用此方法实现的单次调用应该GetProcOrdinal比仅调用. 也许更重要的是，这种方法不依赖于任何未知数（即序数）。这种方法的缺点是它不像其他方法那么简单。GetProcAddress

您可以使用调试帮助库来帮助避免对 PE 文件映像进行一些解析（这是我最初所做的），但事实证明，解析 PE 映像的所需部分并不难。我认为避免对调试帮助库的依赖是值得解析 PE 图像头所需的最小额外努力。

言归正传，下面是 C 语言的一个示例实现：

#include <stdio.h>

#include "windows.h"

/// Efficiently searches a module's name pointer table (NPT) for the named
/// procedure.
///
/// @param[in] npt     Address of the NPT to search.
///
/// @param[in] size    Number of entries in the NPT.
///
/// @param[in] base    Base address of the module containing the NPT. This is
///                    used to resolve addresses in the NPT (which are relative
///                    to the module's base address).
///
/// @param[in] proc    String containing the name of the procedure to search
///                    for.
///
/// @return    Returns the index into the NPT of the entry matching the named
///            procedure. If no such matching entry exists, the function returns
///            -1.
///
DWORD FindNptProc (PDWORD npt, DWORD size, PBYTE base, LPCSTR proc)
{
    INT   cmp;
    DWORD max;
    DWORD mid;
    DWORD min;

    min = 0;
    max = size - 1;

    while (min <= max) {
        mid = (min + max) >> 1;
        cmp = strcmp((LPCSTR)(npt[mid] + base), proc);
        if (cmp < 0) {
            min = mid + 1;
        } else if (cmp > 0) {
            max = mid - 1;
        } else {
            return mid;
        }
    }

    return -1;
}

/// Gets a pointer to a module's export directory table (EDT).
///
/// @param[in] module    Handle to the module (as returned by GetModuleHandle).
///
/// @return    Returns a pointer to the module's EDT. If there is an error (e.g.
///            if the module handle is invalid or the module has no EDT) the
///            function will return NULL.
///
PIMAGE_EXPORT_DIRECTORY GetExportDirectoryTable (HMODULE module)
{
    PBYTE                   base; // base address of module
    PIMAGE_FILE_HEADER      cfh;  // COFF file header
    PIMAGE_EXPORT_DIRECTORY edt;  // export directory table (EDT)
    DWORD                   rva;  // relative virtual address of EDT
    PIMAGE_DOS_HEADER       mds;  // MS-DOS stub
    PIMAGE_OPTIONAL_HEADER  oh;   // so-called "optional" header
    PDWORD                  sig;  // PE signature

    // Start at the base of the module. The MS-DOS stub begins there.
    base = (PBYTE)module;
    mds = (PIMAGE_DOS_HEADER)module;

    // Get the PE signature and verify it.
    sig = (DWORD *)(base + mds->e_lfanew);
    if (IMAGE_NT_SIGNATURE != *sig) {
        // Bad signature -- invalid image or module handle
        return NULL;
    }

    // Get the COFF file header.
    cfh = (PIMAGE_FILE_HEADER)(sig + 1);

    // Get the "optional" header (it's not actually optional for executables).
    oh = (PIMAGE_OPTIONAL_HEADER)(cfh + 1);

    // Finally, get the export directory table.
    if (IMAGE_DIRECTORY_ENTRY_EXPORT >= oh->NumberOfRvaAndSizes) {
        // This image doesn't have an export directory table.
        return NULL;
    }
    rva = oh->DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress;
    edt = (PIMAGE_EXPORT_DIRECTORY)(base + rva);

    return edt;
}

/// Gets the ordinal of an exported procedure.
///
/// @param[in] module    Handle (as returned by GetModuleHandle) of the module
///                      that exports the procedure.
///
/// @param[in] proc      String containing the name of the procedure.
///
/// @return    Returns the procedure's ordinal. If an ordinal for the procedure
///            could not be located (e.g. if the named procedure is not exported
///            by the specified module) then the function will return -1.
///
DWORD GetProcOrdinal (HMODULE module, LPCSTR proc)
{
    PBYTE                   base; // module base address
    PIMAGE_EXPORT_DIRECTORY edt;  // export directory table (EDT)
    PWORD                   eot;  // export ordinal table (EOT)
    DWORD                   i;    // index into NPT and/or EOT
    PDWORD                  npt;  // name pointer table (NPT)

    base = (PBYTE)module;

    // Get the export directory table, from which we can find the name pointer
    // table and export ordinal table.
    edt = GetExportDirectoryTable(module);

    // Get the name pointer table and search it for the named procedure.
    npt = (DWORD *)(base + edt->AddressOfNames);
    i = FindNptProc(npt, edt->NumberOfNames, base, proc);
    if (-1 == i) {
        // The procedure was not found in the module's name pointer table.
        return -1;
    }

    // Get the export ordinal table.
    eot = (WORD *)(base + edt->AddressOfNameOrdinals);

    // Actual ordinal is ordinal from EOT plus "ordinal base" from EDT.
    return eot[i] + edt->Base;
}

int main (int argc, char *argv [])
{
    LPCSTR  procName;
    HMODULE module = NULL;
    LPCSTR  moduleName;
    DWORD   ordinal;

    if (argc != 3) {
        printf("A DLL name and procedure name must be specified\n");
        return EXIT_FAILURE;
    }

    moduleName = argv[1];
    procName   = argv[2];

    if (NULL == LoadLibrary(moduleName)) {
        printf("Could not load library %s\n", moduleName);
        return EXIT_FAILURE;
    }

    module = GetModuleHandle(moduleName);
    if (NULL == module) {
        printf("Couldn't get a handle to %s\n", moduleName);
        return EXIT_FAILURE;
    }

    ordinal = GetProcOrdinal(module, procName);
    if (-1 == ordinal) {
        printf("Could not find ordinal for %s in %s\n", procName, moduleName);
    } else {
        printf("Found %s at ordinal %d\n", procName, ordinal);
    }

    return EXIT_SUCCESS;
}

GetProcOrdinal是有趣的部分发生的地方。该代码希望是相当不言自明的；然而，要完全理解它可能需要一些关于 PE 文件格式的知识，我不打算在这里讨论（网上有很多关于它的信息）。FindNptProc只是一个对 NPT 进行二分查找的便捷函数。GetExportDirectoryTable是另一个方便的函数，它解析 PE 标头以定位导出目录表。

上面的代码在 Visual Studio 2008 和 Windows XP (SP3) 下为我编译干净，但 YMMV。我不是一个真正的 Windows 人*，所以这可能不是最干净的代码可移植性（就不同版本的 Windows 而言）。像往常一样，此代码按“原样”提供，不提供任何形式的保证；）

*Yes, in case you're wondering, I do still feel kind of dirty after writing all that Microsoft-style Windows code.

Answer 2

一种丑陋的方法是使用 dumpbin 命令运行系统调用并解析输出。但这与众所周知的瓷器店里的公牛一样优雅。

dumpbin /exports c:\windows\system32\user32.dll | grep FunctionOfInterest

否则，您可以编写一个简单的循环，使用序数调用GetProcAddress（传入 name 参数的低两个字节）。当函数指针与传递实际名称时返回的指针匹配时，就完成了。

这是没有错误检查的基本思想：

  HANDLE hMod;
  HANDLE byname, byord;
  int ord;

  hMod = LoadLibrary( "user32.dll" );
  byname = GetProcAddress( hMod, "GetWindow" );
  byord = 0;
  ord = 1;
  while ( 1 ) {
     byord = GetProcAddress( hMod, (LPCSTR)ord );
     if ( byord == byname ) {
        printf( "ord = %d\n", ord );
        break;
        }
     ord++;
     }