The Microsoft C/C++ compiler allows you to specify link order of functions or variables. Using the #pragma directive with either code_seg or data_seg and specifying the segment name and its sorting key, you can tell the linker how to place the object code in the final executable.

Let’s start with a simple example:

#pragma code_seg(push, ".text$EB009")
__declspec(noinline) void f1()
{
    printf("this is f1()\n");
}
#pragma code_seg(pop)


#pragma code_seg(push, ".text$EB005")
__declspec(noinline) void f2()
{
    printf("this is f2()\n");
}
#pragma code_seg(pop)


#pragma code_seg(push, ".text$EB001")
__declspec(noinline) void f3()
{
    printf("this is f3()\n");
}
#pragma code_seg(pop)

int main()
{
    f1();
    f2();
    f3();
    return 0;
}

When the code_seg pragma is used, we can specify where the subsequent code should lie (in which section in the PE file). When the section name contains the “$” sign, then the subsequent text is not part of the section name (the string prior to the “$”) and instead is used as a sorting key. Continue reading “Shuffling function addresses in C/C++ with MSVC”