My JmpDetour

[Jimster480]

DWORD JmpDetour(DWORD OA, DWORD DA) //Credits Jimster480
{
    BYTE* DOA = (BYTE*)OA;BYTE* DDA = (BYTE*)DA;
    DWORD OP;
    BYTE* COC = (BYTE*)OA;
    int COS =+ oplen(COC);
    COC += COS;

    while(COS < 5)
    {
        int l = oplen(COC);
        if(!l) return NULL;
        COS += l;
        COC += l;
    }
    DWORD BL = (DWORD)(COC - DOA);
    BYTE* DRT = (BYTE*)VirtualAlloc(NULL, 5 + BL, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE); 

    if(!VirtualProtect(DOA,BL,PAGE_READWRITE,&OP)) return NULL;

    if(!memcpy(DRT,DOA,BL)) return NULL;
    DRT = DRT + BL;

    DRT[0] = 0xE9;
    *(DWORD*)(DRT + 1) = (DWORD)(DOA + BL - DRT)-5;

    DOA[0] = 0xE9;
    *(DWORD*)(DOA + 1) = (DWORD)(DDA - DOA)-5;

    for(DWORD N = 5;N<BL;N++) {DOA[N] = 0x90;}
 
    if(!VirtualProtect(DOA,BL,OP,&OP)) return NULL;

    FlushInstructionCache(GetCurrentProcess(), NULL, 0);

    return (((DWORD)DRT) - BL);
}

Documented

DWORD JmpDetour(DWORD OA, DWORD DA) // Syntax: Original Function Name (Ex: glBegin), New (Detoured) Function Name (Ex: h_glBegin)
{
    BYTE* DOA = (BYTE*)OA; // Reassign Orig Address As A Byte (Detour Address)
    BYTE* DDA = (BYTE*)DA; // Reassign Target Address As A Byte
    DWORD OP; // Old Protect For VirtualProtect
    BYTE* COC = (BYTE*)OA; // Current Opcode Of Current Address
    int COS =+ oplen(COC); // Length Of Current Opcode
    COC += COS; // Current Opcode + Current Opcode Length

    while(COS < 5) // Address Opcode Length Finding Loop
    {
        int l = oplen(COC); // Length Of Current Opcode
        if(!l) return NULL; // If Current Opcode Has No Length The Function Fails
        COS += l; // Opcode Length + Current Opcode Length
        COC += l; // Current Opcode + Current Opcode Length (Next Opcode)
    }
    DWORD BL = (DWORD)(COC - DOA); // Number (Length) Of Bytes At Detour Address
    BYTE* DRT = (BYTE*)malloc(5 + BL); // Detour Return JmpGate Creation (JMPDETOUR Length + Length Of Bytes At Detour Address)
 
    if(!VirtualProtect(DOA,BL,PAGE_READWRITE,&OP)) return NULL; // Set Memory Flags For Detour Address, If Unable To Set, The Function Fails

    if(!memcpy(DRT,DOA,BL)) return NULL; // Copy The Opcodes At The Detour Address To The JmpGate We Made
    DRT = DRT + BL; // Move The EIP Forward At The JmpGate So It Passes The Opcodes We Just Copied (To Prevent OverWriting)

    DRT[0] = 0xE9; // Write The JMP Opcode At The Current JmpGate Address
    *(DWORD*)(DRT + 1) = (DWORD)(DOA + BL - DRT) - 5; // Write Return Address After JMP Opcode  (Orig Address + Byte Length At Detour Address - Current JmpGate Length) - JMPDETOUR Length

    DOA[0] = 0xE9; // Write The JMP Opcode At Detour Address
    *(DWORD*)(DOA + 1) = (DWORD)(DDA - DOA) - 5; // Write New (Detoured) Function Address After JMP Opcode (Target Address - Detour Address) - JMPDETOUR Length
 
    if(!VirtualProtect(DOA,BL,OP,&OP)) return NULL; // Reset Memory Flags For Detour Address, If Unable To Set, The Function Fails

    return (((DWORD)DRT) - BL); // Return Return JmpGate Address (JmpGate Address - Byte Length At Detour Address)
}

use the NT_DDK.h that is in this section aswell.