Porting 64bit code to 32bit machine

Question

I have seen many people asking porting issues from 32bit to 64bit machine. But is it not common to port code written on 64bit to 32bit. I am trying to port a plugin from 64bit to 32bit in C,but facing similar issues in cases like storing void * to 64bit integers and vice versa.

Whats should be approach in changing the code such that same code works on both(i386 & x86_64) machines? I don't think it make sense to use uint64_t * on a 32 bit machine in place of void* which is 32bit? Does some generalized approach exists for such cases?

Answer 1

Pointers should never be stored in fixed-size integers. If you need to store a pointer in an integer type, the correct type is uintptr_t, but you really should not be storing pointers in integer objects at all. However, there's no real harm in using an integer type that's too large; it will just waste a little bit of memory. So if storing pointers in uint64_t is the only issue in your code, it should work fine compiled for 32-bit targets.

Answer 2

As you know, You can write one source code for both 32bit and 64bit architectures with a series of "#define", "#ifdef" etc which are pre-processor directives. You need to compile the source once for 32bit and 64bit each. This can be something like this.

test.c sample code

#ifdef ARCH_64
    typedef UINT unit64_t;
#else
    typedef UINT unit32_2;

UINT  *my_uint_ptr;

$ gcc -m32 test.c

$ gcc -m64 -DARCH_64 test.c