Loading and executing code directly from an obj file on Windows!

build.bat

@echo off

rem Set up the Visual Studio 2013 compiler environment variables
call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x64

cl -c lib.cpp
cl runner.cpp /link user32.lib

lib.cpp

int add(int a, int b) {
    return a + b;
}

runner.cpp

#include <windows.h>

typedef int (*Add)(int, int);
#define Read16(Ptr) ((*((Ptr) + 1) << 8) | (*((Ptr) + 0) << 0))
#define Read32(Ptr) ((*((Ptr) + 3) << 24) | (*((Ptr) + 2) << 16) | \
                     (*((Ptr) + 1) << 8 ) | (*((Ptr) + 0) << 0 ))

void *FindTextSection(unsigned char *FileText) {
    int NumberOfSections = Read16(FileText + 2);
    unsigned char *SectionTable = FileText + 0x14;
    for (int SecTableIdx = 0; SecTableIdx < NumberOfSections; ++SecTableIdx) {
        if (SectionTable[0] == '.' &&
            SectionTable[1] == 't' &&
            SectionTable[2] == 'e' &&
            SectionTable[3] == 'x' &&
            SectionTable[4] == 't')
        {
            break;
        }
        SectionTable += 0x28;
    }

    unsigned char *PointerToRawData = SectionTable + 0x14;
    int TextOffset = Read32(PointerToRawData);
    return (void *) (FileText + TextOffset);
}

int main(int argc, char *argv[]) {
    HANDLE FileHandle = CreateFile("lib.obj",
                                   GENERIC_READ | GENERIC_EXECUTE,
                                   FILE_SHARE_READ, 0,
                                   OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
    if (FileHandle == INVALID_HANDLE_VALUE) {
        MessageBoxA(0, "lib.obj not found", "Error", MB_OK);
        return 1;
    }

    HANDLE MappingHandle = CreateFileMapping(FileHandle, 0, PAGE_EXECUTE_READ, 0, 0, 0);
    if (MappingHandle == 0) {
        CloseHandle(FileHandle);
        char str[64];
        wsprintf(str, "Could not map file (%d)", GetLastError());
        MessageBoxA(0, str, "Error", MB_OK);
        return 1;
    }

    void *Address = MapViewOfFile(MappingHandle, FILE_MAP_EXECUTE | FILE_MAP_READ,
                                  0, 0, 0);
    if (Address == 0) {
        CloseHandle(FileHandle);
        CloseHandle(MappingHandle);
        char str[64];
        wsprintf(str, "Could not map view of file (%d)", GetLastError());
        MessageBoxA(0, str, "Error", MB_OK);
        return 1;
    }

    CloseHandle(FileHandle);
    CloseHandle(MappingHandle);

    void *TextSection = FindTextSection((unsigned char *) Address);
    Add add = (Add) (TextSection);

    char str[2] = ".";
    wsprintf(str, "%d", add(1, 1));
    MessageBoxA(0, str, "Result", MB_OK);

    UnmapViewOfFile(Address);

    return 0;
}