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Writing a kd/WinDbg Debugger Extension DLL


December 1998/Writing a kd/WinDbg Debugger Extension DLL/Listing 1

Listing 1: ext.c — Sample debugger extensions

#include "wdjexts.h"

// hello_dbg
//  simple extension
DECLARE_API(hello_dbg)
{
    // print a message to the debug console using the raw callback
    // function supplied by ExtensionApis.
    (ExtensionApis.lpOutputRoutine)("Hello, Debugger!\n");

    dprintf(" hCurrentProcess = %Xh\n", hCurrentProcess);
    dprintf(" hCurrentThread  = %Xh\n", hCurrentThread);
    dprintf(" dwProcessor     = %Xh\n", dwProcessor);
    dprintf(" dwCurrentPc     = %Xh\n", dwCurrentPc);

    // note that either args will be NULL or args[0] will
    // be 0 if no arguments were specified, depending on
    // the debugger.
    dprintf(" args            = \"%s\"\n", 
        args && args[0] ? args : "<none>");
}

// WinDbg will invoke this routine when the user invokes either
// !wdjext.help or simply !wdjext.?.
DECLARE_API(help)
{
    dprintf("hello_dbg               ");
    dprintf("Example routine that prints out args\n");
    dprintf("dis <code address>      ");
    dprintf("Disassembles an instruction at <address>\n");
    dprintf("eflags                  ");
    dprintf("Shows EFLAGS register contents\n");
    dprintf("mdl <MDL *>             ");
    dprintf("Dumps an MDL structure\n");
    dprintf("special_regs            ");
    dprintf("Displays special registers like GDTR and TRx\n");
    dprintf("getkrnlver              ");
    dprintf("Displays information about the remote kernel\n");
}

// dis
//  demonstrates the use of the Disassm() API
DECLARE_API(dis)
{
    ULONG Address;
    CHAR Buffer[256];  // better safe than sorry
    ULONG rc;
    UINT Displacement;

    if (!args || !args[0])      {
        dprintf("usage: dis <code address>\n");
        return;
    }

    // Get the address at which to disassemble
    Address = GetExpression(args);
    if (!Address)       {
        dprintf("Couldn't evaluate expression \"%s\"\n", args);
        return;
    }

    // Get and print the symbolic name for this address.  Note
    // that Buffer must be large enough to hold any symbol or
    // it will be overwritten.
    GetSymbol( (PVOID)Address, &Buffer[0], &Displacement);

    dprintf("%s+%d:\n", Buffer, Displacement);

    // Disassemble the instruction at the given address.  Again,
    // Buffer had better be big enough.  On return, Address will 
    // point to the next instruction.
    rc = Disassm( &Address, (PCHAR)&Buffer,     FALSE);
            
    if (rc) dprintf("%s", Buffer);
    else    dprintf("Disassembly failed at %Xh\n", Address);
}

DECLARE_API(mdl)
{
    ULONG       rc;
    DWORD       MdlAddress;
    CSHORT      MdlSize;
    PMDL        Mdl;
    ULONG       BytesRead;
    PULONG      CurrentPage, EndPage;

    if (!args || !args[0])      {
        dprintf("usage: mdl <MDL address>\n");
        return;
    }

    MdlAddress = GetExpression(args);
    if (!MdlAddress)    {
        dprintf("Couldn't evaluate expression \"%s\"\n", args);
        return;
    }

    // First, read the size so we know how much memory to allocate
    rc = ReadMemory( MdlAddress + FIELD_OFFSET(MDL, Size), 
                     &MdlSize, sizeof(MdlSize), &BytesRead );
    if (!rc || BytesRead != sizeof(MdlSize) )   {
        dprintf("Failed to read memory at %Xh\n", MdlAddress);
        return;
    }

    // sanity check on size.  We'll let it go, but we only dump out
    // the base structure.
    if ( MdlSize < sizeof(MDL) || MdlSize > (CSHORT)0x400 )     {
        dprintf("WARNING: Mdl size is %d bytes; probably not a "
                "valid MDL.\n", MdlSize);
        MdlSize = sizeof(MDL);
    }

    Mdl = (PMDL) LocalAlloc( LPTR, MdlSize );
    if (!Mdl)   {
        dprintf("Failed to allocate memory!\n");
        return;
    }

    // read in the entire MDL
    rc = ReadMemory( (ULONG)MdlAddress, Mdl, MdlSize, &BytesRead );
    if (!rc || BytesRead != (ULONG)MdlSize)     {
        dprintf("Failed to read memory at %Xh\n", MdlAddress);
        LocalFree( Mdl );
        return;
    }

    // dump it
    dprintf("MDL at %X:\n", MdlAddress);
    dprintf("  Next:              %08X\n", Mdl->Next);
    dprintf("  Size:                  %04Xh\n", Mdl->Size);
    dprintf("  Flags:                 %04Xh\n", Mdl->MdlFlags);
#define PRINT_FLAG(_f)  \
    if (Mdl->MdlFlags & _f) dprintf("    %s\n", #_f);
    PRINT_FLAG(MDL_MAPPED_TO_SYSTEM_VA);
    PRINT_FLAG(MDL_PAGES_LOCKED);
    PRINT_FLAG(MDL_SOURCE_IS_NONPAGED_POOL);
    PRINT_FLAG(MDL_ALLOCATED_FIXED_SIZE);
    PRINT_FLAG(MDL_PARTIAL);
    PRINT_FLAG(MDL_PARTIAL_HAS_BEEN_MAPPED );
    PRINT_FLAG(MDL_IO_PAGE_READ);
    PRINT_FLAG(MDL_WRITE_OPERATION);
    PRINT_FLAG(MDL_PARENT_MAPPED_SYSTEM_VA);
    PRINT_FLAG(MDL_LOCK_HELD );
    PRINT_FLAG(MDL_SYSTEM_VA);
    PRINT_FLAG(MDL_IO_SPACE);
    PRINT_FLAG(MDL_NETWORK_HEADER );
    PRINT_FLAG(MDL_MAPPING_CAN_FAIL);
    PRINT_FLAG(MDL_ALLOCATED_MUST_SUCCEED);
#undef PRINT_FLAG

    dprintf("  Process:           %08X\n", Mdl->Process);
    dprintf("  MappedSystemVa:    %08X\n", Mdl->MappedSystemVa);
    dprintf("  StartVa:           %08X\n", Mdl->StartVa);
    dprintf("  ByteCount:         %8X\n", Mdl->ByteCount);
    dprintf("  ByteOffset:        %8X\n", Mdl->ByteOffset);

    dprintf("  Pages:\n");
    CurrentPage = (PDWORD)(Mdl + 1);
    EndPage = (PDWORD)((PCHAR)Mdl + MdlSize);
    while (CurrentPage < EndPage)
        dprintf("    %8X\n", CurrentPage++);

    LocalFree( Mdl );
}

DECLARE_API(eflags)
{
    CONTEXT Context;

    wdjGetContext((USHORT)dwProcessor, &Context);

    if (Context.EFlags & 0x00000001) dprintf("  Carry\n");
    if (Context.EFlags & 0x00000004) dprintf("  Parity\n");
    if (Context.EFlags & 0x00000010) dprintf("  Aux Carry\n");
    if (Context.EFlags & 0x00000040) dprintf("  Zero\n");
    if (Context.EFlags & 0x00000080) dprintf("  Sign\n");
    if (Context.EFlags & 0x00000100) dprintf("  Trap\n");
    if (Context.EFlags & 0x00000200) dprintf("  Interrupt\n");
    if (Context.EFlags & 0x00000400) dprintf("  Direction\n");
    if (Context.EFlags & 0x00000800) dprintf("  Overflow\n");
    if (Context.EFlags & 0x00004000) dprintf("  Nested Task\n");

    dprintf("  I/O Priviledge Level: %d\n", 
        (Context.EFlags && 0x3000) >> 12);
}

DECLARE_API(special_regs)
{
    KSPECIAL_REGISTERS r;

    wdjGetSpecialRegisters((USHORT)dwProcessor, &r);

    dprintf("Cr0=%08X  Cr2=%08X  Cr3=%08X  Cr4=%08X\n",
            r.Cr0, r.Cr2, r.Cr3, r.Cr4);
    dprintf("Dr0=%08X  Dr1=%08X  Dr2=%08X  Dr3=%08X\n", 
            r.KernelDr0, r.KernelDr1, r.KernelDr2, r.KernelDr3);
    dprintf("Dr6=%08X  Dr7=%08X\n",
            r.KernelDr6, r.KernelDr7);
    dprintf("Tr=%04X\n", r.Tr); 
    dprintf("GDT:  Base=%08X  Limit=%04X\n", 
            r.Gdtr.Base, r.Gdtr.Limit);
    dprintf("IDT:  Base=%08X  Limit=%04X\n", 
            r.Idtr.Base, r.Idtr.Limit);
}

DECLARE_API(getkrnlver)
{
    ULONG rc;
    DBGKD_GET_VERSION VersionInfo;

#if EXT_API_VERSION_NUMBER >= 5
    rc = wdjGetKernelVersion(&VersionInfo);
#else
    rc = FALSE; // IG_GET_KERNEL_VERSION not supported
#endif

    if (!rc)    {
        dprintf("Could not get kernel version information!\n");
        return;
    }
    dprintf("MajorVersion:      %d (%04Xh)\n", 
            VersionInfo.MajorVersion, VersionInfo.MajorVersion);
    dprintf("MinorVersion:      %d (%04Xh)\n", 
            VersionInfo.MinorVersion, VersionInfo.MinorVersion);
    dprintf("ProtocolVersion:   %04Xh\n", 
            VersionInfo.ProtocolVersion);
    dprintf("Flags:             %04Xh\n", VersionInfo.Flags);
    dprintf("KernBase:          %08Xh\n", VersionInfo.KernBase);
    dprintf("PsLoadedModuleList:%08Xh\n", 
            VersionInfo.PsLoadedModuleList);
    dprintf("MachineType:       %04Xh\n", VersionInfo.MachineType);
}
//End of File

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