Thunk table in import address table?

Question

What is a thunk table in relation to the import address table that's used in EXE files to import functions used in external DLLs?

Is this thunk table just a table containing 'Thunks' to other functions?

Answer 1

Thunks are a part of the Import table (IMAGE_DIRECTORY_ENTRY_IMPORT) and Delay Import Table (IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT). They are described http://msdn.microsoft.com/en-us/library/ms809762.aspx.

I'll look at my old source code and will post later a working code which dump both this tables inclusive binding information.

UPDATED:

Here is a code which I fond in one of my old program. It support only 32-bit PE, but can be easy modified to 64-bit. By the way you can see, that it dump also binding information.To test this bind the PE which you want to dump with respect of bind.exe (use for example, bind.exe -u -v Test.dll).

The code consist from about 1000 lines, so I could not post it here. I receive an error message

Oops! Your edit couldn't be submitted because:

• body is limited to 30000 characters; you entered 55095

So I placed it here: http://www.ok-soft-gmbh.com/ForStackOverflow/PEInfo.c. I hope the code will help you better as a long description.

UPDATED 2: I see that my old answer is not good for searching engine. So I includes the part of the code of PEInfo.c (the functions DumpImports and DumpExports) below:

void MakeIdent (UINT nOffset)
{
    for (; nOffset; nOffset--)
        printf ("    ");    // 4 blanks
}

void DumpDword (UINT nOffset, LPCSTR pszPrefix, DWORD dw)
{
    MakeIdent(nOffset);

    if (dw < 100)
        printf ("%s: %d\n", pszPrefix, dw);
    else if (dw%(256*256) == 0)
        printf ("%s: 0x%X\n", pszPrefix, dw);
    else
        printf ("%s: %d (0x%X)\n", pszPrefix, dw, dw);
}

void DumpTimeDateStamp (UINT nOffset, LPCSTR pszTimeDateStampPrefix, DWORD dwTimeDateStamp)
{
    //struct tm tmTime;//= localtime_s ((time_t *)&dwTimeDateStamp);
    //errno_t err = localtime_s (&tmTime, ((time_t *)&dwTimeDateStamp));

    struct tm *ptmTime = _localtime32 ((__time32_t *)&dwTimeDateStamp);
    SYSTEMTIME stSystemTime;
    static CHAR szString[128];

    stSystemTime.wYear = (WORD)(1900 + ptmTime->tm_year);
    stSystemTime.wMonth = (WORD)(ptmTime->tm_mon + 1);
    stSystemTime.wDay = (WORD)ptmTime->tm_mday;
    stSystemTime.wDayOfWeek = (WORD)(ptmTime->tm_wday + 1);
    stSystemTime.wHour = (WORD)ptmTime->tm_hour;
    stSystemTime.wMinute = (WORD)ptmTime->tm_min;
    stSystemTime.wSecond = (WORD)ptmTime->tm_sec;
    stSystemTime.wMilliseconds = 0;

    MakeIdent(nOffset);
    printf ("%s: 0x%8X (", pszTimeDateStampPrefix, dwTimeDateStamp);

    if (GetDateFormatA (LOCALE_USER_DEFAULT, 0, &stSystemTime, NULL, 
        szString, sizeof(szString)/sizeof(TCHAR)) != 0) {
        printf (szString);
    }

    if (GetTimeFormatA (LOCALE_USER_DEFAULT, 0, &stSystemTime, NULL, 
                       szString, sizeof(szString)/sizeof(TCHAR)) != 0) {
        if (szString[0] != 0)
            printf (" ");
        printf (szString);
    }
    printf (")\n");
}

void DumpImports (UINT nOffset, IMAGE_OPTIONAL_HEADER32 *pOptionalHeader, PBYTE pbyFile,
                  IMAGE_SECTION_HEADER *pSectionHeader, IMAGE_NT_HEADERS32 *pNtHeader) // header of the section, which contains export section
{
    IMAGE_IMPORT_DESCRIPTOR *pImportDescriptor = (IMAGE_IMPORT_DESCRIPTOR *)((PBYTE)pbyFile + pSectionHeader->PointerToRawData +
        pOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].VirtualAddress - pSectionHeader->VirtualAddress);
    DWORD dwBoundImportVA = pOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT].VirtualAddress;
    IMAGE_BOUND_IMPORT_DESCRIPTOR *pFirstBoundImportDescriptor = NULL, *pBoundImportDescriptor;

    //DumpDword (nOffset, TEXT("Characteristics"), pImportDescriptor->Characteristics);
    if (dwBoundImportVA) {
        UINT i;
        IMAGE_SECTION_HEADER *pFirstSectionHeader = (IMAGE_SECTION_HEADER *)((PBYTE)pOptionalHeader + //sizeof(IMAGE_OPTIONAL_HEADER32));
                                                                                pNtHeader->FileHeader.SizeOfOptionalHeader);

        for (i=0; i<pNtHeader->FileHeader.NumberOfSections; i++) {
            if (pFirstSectionHeader[i].VirtualAddress <= dwBoundImportVA &&
                dwBoundImportVA < pFirstSectionHeader[i].VirtualAddress + pFirstSectionHeader[i].Misc.VirtualSize) {

                pFirstBoundImportDescriptor = (IMAGE_BOUND_IMPORT_DESCRIPTOR *)((PBYTE)pbyFile + pFirstSectionHeader[i].PointerToRawData +
                                            dwBoundImportVA - pFirstSectionHeader[i].VirtualAddress);
                break;
            }
        }
        if (i >= pNtHeader->FileHeader.NumberOfSections)
            pFirstBoundImportDescriptor = (IMAGE_BOUND_IMPORT_DESCRIPTOR *)((PBYTE)pbyFile + dwBoundImportVA);
    }

    for (;pImportDescriptor->Characteristics; pImportDescriptor++) {
        IMAGE_THUNK_DATA *pOriginalFirstThunk = (IMAGE_THUNK_DATA *)((PBYTE)pbyFile + pSectionHeader->PointerToRawData +
            pImportDescriptor->OriginalFirstThunk - pSectionHeader->VirtualAddress);
        IMAGE_THUNK_DATA *pFirstThunk = (IMAGE_THUNK_DATA *)((PBYTE)pbyFile + pSectionHeader->PointerToRawData +
            pImportDescriptor->FirstThunk - pSectionHeader->VirtualAddress);
        IMAGE_THUNK_DATA *pOriginalThunk, *pThunk;

        MakeIdent(nOffset);
        printf ("%s ", pbyFile + pSectionHeader->PointerToRawData + pImportDescriptor->Name - pSectionHeader->VirtualAddress);
        //DumpDword (nOffset, TEXT("Ordinal Base"), pExportDirectory->Base);

        if (pImportDescriptor->TimeDateStamp == 0) {
            //MakeIdent(nOffset);
            printf ("(DLL is Not bound)\n");
        }
        else if (pImportDescriptor->TimeDateStamp == -1) {
            //if bound, and real date\time stamp
            //                                    //     in IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT (new BIND)
            //MakeIdent(nOffset);
            printf ("(DLL bound with New BIND)\n");
        }
        else {
            //MakeIdent(nOffset);
            printf ("(DLL bound with Old BIND) ");
            DumpTimeDateStamp (nOffset, "TimeDateStamp", pImportDescriptor->TimeDateStamp);
        }

        MakeIdent(nOffset+1);
        if (pImportDescriptor->TimeDateStamp)   // if bound
            printf (TEXT("      Ordinal          hint BoundAddrs Name\n"));
        else
            printf (TEXT("      Ordinal          hint Name\n"));

        for (pOriginalThunk=pOriginalFirstThunk, pThunk=pFirstThunk; pOriginalThunk->u1.AddressOfData; pOriginalThunk++, pThunk++) {
            if (IMAGE_SNAP_BY_ORDINAL32(pOriginalThunk->u1.Ordinal)) {
                MakeIdent(nOffset+1);
                // Ordinal
                if (pImportDescriptor->TimeDateStamp)
                    printf (TEXT("%4u (0x%04X)               0x%08X\n"),
                            pOriginalThunk->u1.Ordinal & ~IMAGE_ORDINAL_FLAG32,
                            pOriginalThunk->u1.Ordinal^IMAGE_ORDINAL_FLAG32,
                            pThunk->u1.AddressOfData);
                else
                    // pThunk->u1.AddressOfData == pOriginalThunk->u1.Ordinal so don't print it 
                    printf (TEXT("%4u (0x%04X)\n"),
                            pOriginalThunk->u1.Ordinal & ~IMAGE_ORDINAL_FLAG32,
                            pOriginalThunk->u1.Ordinal^IMAGE_ORDINAL_FLAG32);
            }
            else {
                IMAGE_IMPORT_BY_NAME *pImportByName = (IMAGE_IMPORT_BY_NAME *) (pOriginalThunk->u1.AddressOfData +
                    (PBYTE)pbyFile + pSectionHeader->PointerToRawData - pSectionHeader->VirtualAddress);

                MakeIdent(nOffset+1);
                // Hint - Index into the Export Name Pointer Table. A match is attempted first with this value.
                // If it fails, a binary search is performed on the DLL’s Export Name Pointer Table.
                if (pImportDescriptor->TimeDateStamp)   // if bound
                    printf (TEXT("%18u (0x%04X) 0x%08X %hs\n"), pImportByName->Hint, pImportByName->Hint, pThunk->u1.AddressOfData,
                        pImportByName->Name);
                else
                    printf (TEXT("%18u (0x%04X) %hs\n"), pImportByName->Hint, pImportByName->Hint, pImportByName->Name);
            }
        }
    }

    if (pFirstBoundImportDescriptor) {
        MakeIdent(nOffset);
        printf ("PE Header contains the following bound import information:\n");

        for (pBoundImportDescriptor=pFirstBoundImportDescriptor; pBoundImportDescriptor->TimeDateStamp;
            pBoundImportDescriptor = (IMAGE_BOUND_IMPORT_DESCRIPTOR *)((PBYTE)(pBoundImportDescriptor+1) + pBoundImportDescriptor->NumberOfModuleForwarderRefs*sizeof(IMAGE_BOUND_FORWARDER_REF))) {
            PSTR pszDllName = (PSTR) ((DWORD)pFirstBoundImportDescriptor + pBoundImportDescriptor->OffsetModuleName);
            IMAGE_BOUND_FORWARDER_REF *pRef = (IMAGE_BOUND_FORWARDER_REF *)(pBoundImportDescriptor+1);

            MakeIdent(nOffset+1);
            printf ("Bound to %hs", pszDllName);
            DumpTimeDateStamp (0, "", pBoundImportDescriptor->TimeDateStamp);
            if (pBoundImportDescriptor->NumberOfModuleForwarderRefs) {
                UINT i;

                for (i=0;i<pBoundImportDescriptor->NumberOfModuleForwarderRefs;i++) {
                    PSTR pszDllName = (PSTR) ((DWORD)pFirstBoundImportDescriptor + pRef->OffsetModuleName);

                    MakeIdent(nOffset+2);
                    printf ("Contained forwarders bound to %hs", pszDllName);
                    DumpTimeDateStamp (0, "", pRef->TimeDateStamp);
                }
            }
        }
    }
}

void DumpExports (UINT nOffset, IMAGE_OPTIONAL_HEADER32 *pOptionalHeader, PBYTE pbyFile,
                  IMAGE_SECTION_HEADER *pSectionHeader) // header of the section, which contains export section
{
    UINT i;
    UINT iNames;
    PDWORD pdwAddressOfFunctions;
    PWORD pwOrdinals;
    PDWORD pdwNameRVA;
    IMAGE_EXPORT_DIRECTORY *pExportDirectory = (IMAGE_EXPORT_DIRECTORY *)((PBYTE)pbyFile + pSectionHeader->PointerToRawData +
        pOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress - pSectionHeader->VirtualAddress);
    DWORD dwVAExportStart = pOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress;
    DWORD dwVAExportEnd = pOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress + 
                          pOptionalHeader->DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].Size;

    DumpDword (nOffset, TEXT("Characteristics"), pExportDirectory->Characteristics);
    DumpTimeDateStamp (nOffset, "TimeDateStamp", pExportDirectory->TimeDateStamp);

    MakeIdent(nOffset);
    printf ("DllName: %s\n", pbyFile + pSectionHeader->PointerToRawData + pExportDirectory->Name - pSectionHeader->VirtualAddress);
    DumpDword (nOffset, TEXT("Ordinal Base"), pExportDirectory->Base);

    MakeIdent(nOffset);
    printf (TEXT("Version: %d.%d\n"), pExportDirectory->MajorVersion, pExportDirectory->MinorVersion);

    DumpDword (nOffset, TEXT("Number of exported functions"), pExportDirectory->NumberOfFunctions);
    DumpDword (nOffset, TEXT("Number of functions exported by name"), pExportDirectory->NumberOfNames);

    MakeIdent(nOffset+1);
    printf (TEXT("Ordn hint RVA      Name\n"));

    pdwAddressOfFunctions = (PDWORD)(pbyFile + pSectionHeader->PointerToRawData + pExportDirectory->AddressOfFunctions - pSectionHeader->VirtualAddress);
    pwOrdinals = (PWORD)(pbyFile + pSectionHeader->PointerToRawData + pExportDirectory->AddressOfNameOrdinals - pSectionHeader->VirtualAddress);
    pdwNameRVA = (PDWORD)(pbyFile + pSectionHeader->PointerToRawData + pExportDirectory->AddressOfNames - pSectionHeader->VirtualAddress);

    for (iNames = 0; iNames < pExportDirectory->NumberOfNames; iNames++) {
        MakeIdent(nOffset+1);

        // AddressOfFunctions MUST be ouf of Export Directory. If it is not so, it is a Forwarding entry
        if (pdwAddressOfFunctions[pwOrdinals[iNames]] < dwVAExportStart ||
            pdwAddressOfFunctions[pwOrdinals[iNames]] > dwVAExportEnd)
            // AddressOfFunctions is normaly in .text section and export table in .edata or .rdata section, so
            // AddressOfFunctions must be not in Export Directory
            printf("%4u %4u %08X %s\n",
                    pwOrdinals[iNames] + pExportDirectory->Base, iNames, pdwAddressOfFunctions[pwOrdinals[iNames]],
                    (pbyFile + pSectionHeader->PointerToRawData + pdwNameRVA[iNames] - pSectionHeader->VirtualAddress));
        else
            printf("%4u %4u          %s (forwarded to %s)\n",
                    pwOrdinals[iNames] + pExportDirectory->Base, iNames,
                    (pbyFile + pSectionHeader->PointerToRawData + pdwNameRVA[iNames] - pSectionHeader->VirtualAddress),
                    (PSTR)(pbyFile + pSectionHeader->PointerToRawData + pdwAddressOfFunctions[pwOrdinals[iNames]] - pSectionHeader->VirtualAddress));
    }

    // print functions exported by ordinal
    for (i = 0; i < pExportDirectory->NumberOfFunctions; i++) {
        if (pdwAddressOfFunctions[i] != 0) {
            // if EXPORTS in DEF-file look like 
            //
            // EXPORTS
            //    Message1  @100
            //    Message2  @200
            //    Message3  @300
            //    Message4  @400
            //    Message5  @500
            // it will be added in export section 401 (500-100+1) entries. 5 from there with not 0 address and the rest
            // empty entries with 0
            // we will dump only not empty entries

            UINT iNames;
            WORD wOrdinal = (WORD)(i + pExportDirectory->Base);

            // try to find (i + pExportDirectory->Base) ordinal in the list of pwOrdinals
            for (iNames = 0; iNames<pExportDirectory->NumberOfNames; iNames++) {
                if (pdwAddressOfFunctions[pwOrdinals[iNames]] == pdwAddressOfFunctions[i])
                    break;
            }

            if (iNames >= pExportDirectory->NumberOfNames) {
                // if not found as exported by name, print it here
                MakeIdent(nOffset+1);
                if (pdwAddressOfFunctions[i] < pSectionHeader->VirtualAddress ||
                    pdwAddressOfFunctions[i] > pSectionHeader->VirtualAddress + pSectionHeader->Misc.VirtualSize)
                    printf("%4u      %08X [NONAME]\n", wOrdinal, pdwAddressOfFunctions[i]);
                else
                    printf("%4u               [NONAME] (forwarded to %s)\n",
                           wOrdinal, (PSTR)(pbyFile + pSectionHeader->PointerToRawData + pdwAddressOfFunctions[i] - pSectionHeader->VirtualAddress));
            }
        }
    }
}