Win32 程序调用 DLL 的机制 

　　 Win32 EXE 在调用一个外部 DLL 中的函数时，首先要调用 LoadLibary 函数来载入此 DLL 到程序的进程地址空间。如果 LoadLibary 载入此 DLL 成功，将返回一个该 DLL 的句柄。 这个句柄实际上就是该 DLL 在内存中的起始地址。 在载入 DLL 成功后，还必须调用 GetProcAddress 函数来获取要调用的函数的地址。然后再根据该地址来调用这个函数。 根据上述原理，我们可以把一个 DLL 作为资源文件放到 EXE 文件中，在程序运行时，分配一块内存，然后将此资源复制到该分配的内存中，并根据该内存地址计算得到相关的导出函数地址，然后，当我们需要调用某一函数时，可以用该函数在内存中的地址来调用它。 程序实现。 　　首先，把要合并的 DLL 作为资源加入到项目的资源文件中，然后在程序运行时，从资源中载入该资源，以得到该 DLL 在内存中的位置：

LPVOID sRawDll; // 资源文件在内存中的地址 HRSRC hRes; HMODULE hLibrary; HGLOBAL hResourceLoaded; char lib_name[MAX_PATH]; GetModuleFileName(hInstance, lib_name, MAX_PATH ); // 得到运行程序的名字 hLibrary = LoadLibrary(lib_name);                  // 就象载入一个 DLL 一样载入运行程序到内存中 if (NULL != hLibrary) {	// 得到指定的资源文件在内存中的位置 	hRes = FindResource(hLibrary, MAKEINTRESOURCE(IDR_DATA1), RT_RCDATA); 	if (NULL != hRes) 	{		// 将资源文件载入内存 		hResourceLoaded = LoadResource(hLibrary, hRes); 		if (NULL != hResourceLoaded) 		{			// 得到资源文件大小 			SizeofResource(hLibrary, hRes); 			// 锁定资源以得到它在内存中的地址 			sRawDll = (LPVOID)LockResource(hResourceLoaded); 		}	}	else return 1; 	FreeLibrary(hLibrary);}else return 1;

然后，从资源中载入 DLL 到内存函数 LoadPbDllFromMemory 将载入 DLL 到内存中，该函数有两个参数，第一个参数是指向 DLL 资源在内存中的地址的指针，也就是前面代码中的 LockResource 函数的返回值。第二个参数是一个空的指针，如果函数 LoadPbDllFromMemory 运行成功，该指针将指向重新组合后的内存中的 DLL 的起始地址。该函数还有一个功能就是如果运行成功，它将手动地用 DLL_PROCESS_ATTACH 参数调用 DLL 的入口函数 DllMain 来初始化该 DLL。除此之外，它还会手动地载入合并的 DLL 的入口表中导入的 DLL 并调整它们在内存中的相对地址。以下是该函数代码:

DWORD LoadPbDllFromMemory(LPVOID lpRawDll, LPVOID lpImageDll) {	SYSTEM_INFO sSysInfo; 	PIMAGE_DOS_HEADER dosHeader; 	PIMAGE_NT_HEADERS pNTHeader; 	PIMAGE_SECTION_HEADER section; 	PIMAGE_IMPORT_DESCRIPTOR pImportDesc; 	PIMAGE_IMPORT_BY_NAME pOrdinalName; 	PIMAGE_BASE_RELOCATION baseReloc; 	PDWORD lpLink; 	unsigned char Protection[4096]; 	HINSTANCE hDll; 	WORD i; 	DWORD ImagePages,fOldProtect,j,MaxLen,HdrLen,Addr1,Addr2,Pg,Pg1,Pg2; 	char * sDllName; 	if(NULL == lpRawDll) return 1 ; 	dosHeader = (PIMAGE_DOS_HEADER)lpRawDll; 	// Is this the MZ header? 	if ((TRUE == IsBadReadPtr(dosHeader,sizeof (IMAGE_DOS_HEADER))) ||				 (IMAGE_DOS_SIGNATURE != dosHeader->e_magic)) 		return 2; 	// Get the PE header. 	pNTHeader = MakePtr(PIMAGE_NT_HEADERS,dosHeader,dosHeader->e_lfanew); 	// Is this a real PE image? 	if((TRUE == IsBadReadPtr(pNTHeader,sizeof ( IMAGE_NT_HEADERS))) || 				( IMAGE_NT_SIGNATURE != pNTHeader->Signature)) 		return 3 ; 	if(( pNTHeader->FileHeader.SizeOfOptionalHeader != 			sizeof(pNTHeader->OptionalHeader)) || 		(pNTHeader->OptionalHeader.Magic != IMAGE_NT_OPTIONAL_HDR32_MAGIC)) 		return 4; 	if (pNTHeader->FileHeader.NumberOfSections < 1) return 5; 	section = IMAGE_FIRST_SECTION( pNTHeader ); 	int HeaderSize = sizeof(IMAGE_SECTION_HEADER); 	// 节头长度 	HdrLen = (DWORD)section - (DWORD)dosHeader + 			HeaderSize * pNTHeader->FileHeader.NumberOfSections; 	// 找出最大的节的长度,此节一般是代码所在的节(.text 节) 	MaxLen = HdrLen; 	int ii=0; 	for (i = 0;i<(DWORD)pNTHeader->FileHeader.NumberOfSections;i++)// find MaxLen 	{		if(MaxLen < section[i].VirtualAddress + section[i].SizeOfRawData) 		{			MaxLen = section[i].VirtualAddress + section[i].SizeOfRawData; 		}		if(strcmp((const char *)section[i].Name,".rsrc") == 0) ii=i; 	}	GetSystemInfo(&sSysInfo);	ImagePages = MaxLen / sSysInfo.dwPageSize; 	if (MaxLen % sSysInfo.dwPageSize) ImagePages++; 	// 分配所需的内存 	DWORD NeededMemory = ImagePages * sSysInfo.dwPageSize; 	lpImageDll = VirtualAlloc(NULL, NeededMemory, MEM_COMMIT, PAGE_EXECUTE_READWRITE); 	if (lpImageDll == NULL) return 6; // 分配内存失败 	MoveMemory( lpImageDll, lpRawDll, HdrLen ); // 复制节头 	DWORD OrgAddr = 0; 	DWORD NewAddr = 0; 	DWORD Size = 0; 	// 复制 .text 节数据 	for (i = 0;i
    
     FileHeader.NumberOfSections;i++) 	{		OrgAddr = (DWORD)lpImageDll + (DWORD)section[i].VirtualAddress; 		NewAddr = (DWORD)lpRawDll + (DWORD)section[i].PointerToRawData; 		Size = (DWORD)section[i].SizeOfRawData; 		MoveMemory((void *)OrgAddr, (void *)NewAddr, Size ); 	}	// 把指针指向新的 DLL 映像 	dosHeader = (PIMAGE_DOS_HEADER) lpImageDll; // Switch to new image 	pNTHeader = (PIMAGE_NT_HEADERS) ((DWORD)dosHeader + dosHeader->e_lfanew); 	section = (PIMAGE_SECTION_HEADER) ((DWORD)pNTHeader + sizeof(IMAGE_NT_HEADERS)); 	pImageBase = (PBYTE)dosHeader; 	if((ii!=0) && (IsNT()==TRUE)) 	{		section[ii].VirtualAddress = section[ii].VirtualAddress + (DWORD)lpRawDll; 		section[ii].PointerToRawData = section[ii].PointerToRawData + (DWORD)lpRawDll; 	}	DWORD importsStartRVA; 	// Look up where the imports section is (normally in the .idata section) 	// but not necessarily so. Therefore, grab the RVA from the data dir. 	importsStartRVA = GetImgDirEntryRVA(pNTHeader,IMAGE_DIRECTORY_ENTRY_IMPORT); 	if ( !importsStartRVA ) 	{		VirtualFree(dosHeader,0, MEM_RELEASE); 		return 7; 	}	pImportDesc = (PIMAGE_IMPORT_DESCRIPTOR) pNTHeader->		OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress; 	if(pImportDesc!= 0) 		pImportDesc = (PIMAGE_IMPORT_DESCRIPTOR) ((DWORD)pImportDesc + (DWORD)dosHeader); 	else 	{		VirtualFree(dosHeader,0, MEM_RELEASE); 		return 8; 	}	while (1) // 处理各入口表中的 DLL 	{		// 检查是否遇到了空的 IMAGE_IMPORT_DESCRIPTOR 		if ((pImportDesc->TimeDateStamp==0 ) && (pImportDesc->Name==0)) break; 		// 从磁盘载入必须的 Dll, 		// 注意,载入的 DLL 是合并的 DLL 的入口表中的 DLL, 		// 不是合并到 EXE 中的 DLL 		sDllName = (char *) (pImportDesc->Name + (DWORD)pImageBase); 		hDll = GetModuleHandle(sDllName); 		if (hDll == 0 ) hDll = LoadLibrary(sDllName); 		if (hDll == 0 ) 		{			MessageBox(NULL, "Can''t find required Dll",					"Error in LoadPbDllFromMemory()",0); 			VirtualFree(dosHeader,0, MEM_RELEASE); 			return 9; 		}		DWORD *lpFuncNameRef = (DWORD *) (pImportDesc->OriginalFirstThunk +								 (DWORD)dosHeader); 		DWORD *lpFuncAddr = (DWORD *) (pImportDesc->FirstThunk +								 (DWORD)dosHeader); 		while( *lpFuncNameRef != 0) 		{			pOrdinalName = (PIMAGE_IMPORT_BY_NAME) (*lpFuncNameRef +						 (DWORD)dosHeader); 			DWORD pIMAGE_ORDINAL_FLAG = 0x80000000; 			if (*lpFuncNameRef & pIMAGE_ORDINAL_FLAG) 				*lpFuncAddr = (DWORD) GetProcAddress(hDll,					 (const char *)(*lpFuncNameRef & 0xFFFF)); 			else				*lpFuncAddr = (DWORD) GetProcAddress(hDll,						 (const char *)pOrdinalName->Name); 			if (lpFuncAddr == 0) 			{				VirtualFree(dosHeader,0, MEM_RELEASE); 				return 10;// Can''t GetProcAddress 			}			lpFuncAddr++;			lpFuncNameRef++;		}		pImportDesc++;	}	DWORD TpOffset; 	baseReloc = (PIMAGE_BASE_RELOCATION)((DWORD)pNTHeader->　　　　 OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_BASERELOC].VirtualAddress); 	if (baseReloc !=0) 	{		baseReloc = (PIMAGE_BASE_RELOCATION) ((DWORD)baseReloc + (DWORD)dosHeader); 		while(baseReloc->VirtualAddress != 0) 		{			PWORD lpTypeOffset = (PWORD) ((DWORD)baseReloc +					 sizeof(IMAGE_BASE_RELOCATION)); 			while (lpTypeOffset < (PWORD)((DWORD)baseReloc +						 (DWORD)baseReloc->SizeOfBlock)) 			{				TpOffset = *lpTypeOffset & 0xF000; 				if(TpOffset == 0x3000) 				{					lpLink = (PDWORD) ((DWORD)dosHeader +　　　　　　　　　　　　　　　　　　　　　　             baseReloc->VirtualAddress +                                                      (*lpTypeOffset & 0xFFF)); 					*lpLink = (DWORD)dosHeader +                                             (*lpLink) - pNTHeader->OptionalHeader.ImageBase; 				}				else				{					if (TpOffset != 0) 					{						VirtualFree(dosHeader,0, MEM_RELEASE); 						return 10; 					}				}				lpTypeOffset++;			}			baseReloc = (PIMAGE_BASE_RELOCATION)((DWORD)baseReloc + 				(DWORD)baseReloc->SizeOfBlock); 		}	}	// 取得原始的内存状态 	memset(Protection,0,4096);	for (i = 0;i<=pNTHeader->FileHeader.NumberOfSections;i++) 	{		if (i == pNTHeader->FileHeader.NumberOfSections) 		{			Addr1 = 0; 			Addr2 = HdrLen; 			j = 0x60000000; 		}		else		{			Addr1 = section[i].VirtualAddress; 			Addr2 = section[i].SizeOfRawData; 			j = section[i].Characteristics; 		}		Addr2 += Addr1 - 1; 		Pg1 = Addr1 / sSysInfo.dwPageSize; 		Pg2 = Addr2 / sSysInfo.dwPageSize; 		for(Pg = Pg1 ;Pg<=Pg2;Pg++) 		{			if (j & 0x20000000) Protection[Pg] |= 1; // Execute 			if (j & 0x40000000) Protection[Pg] |= 2; // Read 			if (j & 0x80000000) Protection[Pg] |= 4; // Write 		}	}	// 恢复原始的内存状态 	Addr1 = (DWORD)dosHeader; 	for (Pg = 0 ;Pg<= ImagePages;Pg++) 	{		switch(Protection[Pg])		{		case 2: 			fOldProtect = PAGE_READONLY; 			break;		case 3: 			fOldProtect = PAGE_EXECUTE_READ; 			break;		case 6: 			fOldProtect = PAGE_READWRITE; 			break;		default: 			// Ignore strange combinations			fOldProtect = PAGE_EXECUTE_READWRITE;  			break;		}		if (fOldProtect !=PAGE_EXECUTE_READWRITE) 		{			if (VirtualProtect((void *)Addr1, 				sSysInfo.dwPageSize, 				fOldProtect,				&fOldProtect) == 0) 			{				VirtualFree(dosHeader,0, MEM_RELEASE); 				return 11; 			}		}		Addr1 += sSysInfo.dwPageSize; 	}	EntryPoint = (LPENTRYPOINT) ((DWORD)pNTHeader->OptionalHeader.AddressOfEntryPoint +				 (DWORD)dosHeader); 	LPVOID lpReserved = 0; 	EntryPoint((HINSTANCE)dosHeader, DLL_PROCESS_ATTACH, lpReserved); 	lpImageDll2=lpImageDll;	return 0; }
    

一但 DLL 被正确地载入到内存中，我们就可以通过自定义函数 GetProcAddressDirectly 来获取某函数在内存中的地址，并根据该地址来调用该函数，该函数也有两个参数，第一个参数是指向载入到内存中的 DLL 的起始地址的指针，第二个是要调用的函数的函数名。以下是 GetProcAddressDirectly 函数代码:

DWORD GetProcAddressDirectly(PIMAGE_DOS_HEADER dosHeader, char * FuncName)  { 	PIMAGE_NT_HEADERS pNTHeader;  	PIMAGE_EXPORT_DIRECTORY pExportDir;  	PWORD lpNameOrdinals;  	LPDWORD lpFunctions;  	DWORD * lpName;  	char * lpExpFuncName;  	DWORD i;  	DWORD j;  	char * lpFuncName;  	if(dosHeader->e_magic != IMAGE_DOS_SIGNATURE) return 0;  	pNTHeader = (PIMAGE_NT_HEADERS)((DWORD)dosHeader + dosHeader->e_lfanew);  	if (pNTHeader->Signature != IMAGE_NT_SIGNATURE) return 0;  	if ((pNTHeader->FileHeader.SizeOfOptionalHeader != sizeof(pNTHeader->OptionalHeader)) ||  		(pNTHeader->OptionalHeader.Magic != IMAGE_NT_OPTIONAL_HDR32_MAGIC))  		return 0;  	DWORD exportsStartRVA, exportsEndRVA;  	pImageBase = (PBYTE)dosHeader;  	// Make pointers to 32 and 64 bit versions of the header.  	pNTHeader = MakePtr( PIMAGE_NT_HEADERS, dosHeader,dosHeader->e_lfanew );  	exportsStartRVA = GetImgDirEntryRVA(pNTHeader,IMAGE_DIRECTORY_ENTRY_EXPORT);  	exportsEndRVA = exportsStartRVA +  		GetImgDirEntrySize(pNTHeader, IMAGE_DIRECTORY_ENTRY_EXPORT);  	// Get the IMAGE_SECTION_HEADER that contains the exports. This is  	// usually the .edata section, but doesn''t have to be.  	PIMAGE_SECTION_HEADER header;  	header = GetEnclosingSectionHeader( exportsStartRVA, pNTHeader );  	if ( !header ) return 0;  	INT delta;  	delta = (INT)(header->VirtualAddress - header->PointerToRawData);  	pExportDir = (PIMAGE_EXPORT_DIRECTORY)GetPtrFromRVA(exportsStartRVA, 				pNTHeader, pImageBase);  	pExportDir =(PIMAGE_EXPORT_DIRECTORY) (pNTHeader->	OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);  	if (pExportDir == 0)  	{ 		MessageBox(NULL,"Error in GetProcAddressDirectly()",0,0);  		return 0;  	} 	pExportDir =(PIMAGE_EXPORT_DIRECTORY) ((DWORD)pExportDir + (DWORD)dosHeader);  	lpNameOrdinals =(PWORD)((DWORD)pExportDir->AddressOfNameOrdinals + (DWORD)dosHeader);  	lpName =(LPDWORD) (pExportDir->AddressOfNames + (DWORD)dosHeader);  	lpFunctions =(LPDWORD) (pExportDir->AddressOfFunctions + (DWORD)dosHeader);  	lpFuncName = FuncName;  	if(HIWORD(lpFuncName)!=0 )  	{ 		for( i = 0;i<=pExportDir->NumberOfFunctions - 1;i++)  		{ 			DWORD entryPointRVA = *lpFunctions;  			// Skip over gaps in exported function  			if ( entryPointRVA == 0 ) continue; 			for( j = 0;j<=pExportDir->NumberOfNames-1;j++)  			{ 				if( lpNameOrdinals[j] == i)  				{ 					lpExpFuncName = (char *) (lpName[j] + 							(DWORD)dosHeader);  					if(strcmp((char *)lpExpFuncName,(char *)FuncName)==0)  						return (DWORD) (lpFunctions[i] + 								(DWORD)dosHeader);  				} 			} 		} 	} 	else 	{ 		for (i = 0 ;i<=pExportDir->NumberOfFunctions - 1;i++)  		{ 			if (lpFuncName == (char *)(pExportDir->Base + i))  			{ 				if (lpFunctions[i]) return (unsigned long) (lpFunctions[i] + 							dosHeader);  			} 		} 	} 	return 0;  }

在调用完函数后，不要忘记用 UnloadPbDllFromMemory 来从内存中移去 DLL 以释放分配的内存，该函数还会用 DLL_PROCESS_DETACH 参数调用 DLL 的入口函数 DllMain 来从调用进程的地址空间卸载该 DLL。 以下是 UnloadPbDllFromMemory 函数代码:

DWORD UnloadPbDllFromMemory(PIMAGE_DOS_HEADER dosHeader) {	PIMAGE_NT_HEADERS pNTHeader; 	pNTHeader = (PIMAGE_NT_HEADERS)((DWORD)dosHeader + (DWORD)dosHeader->e_lfanew); 	EntryPoint = (LPENTRYPOINT)(pNTHeader->OptionalHeader.AddressOfEntryPoint +					 (DWORD)dosHeader); 	EntryPoint((HINSTANCE)dosHeader, DLL_PROCESS_DETACH, 0); 	return VirtualFree(dosHeader, 0, MEM_RELEASE); }

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