Determine the size of the CFRuntimeBase at runtime

CFRuntimeBase_struct_size.m

static size_t _CFRuntimeBaseGetSize()
{
    static size_t sSize = 0;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        // CFUUID has a very nice feature in that it's structure
        // is always the CFRuntimeBase struct (which we don't have access to)
        // followed by a UUID in bytes.
        // By simply traversing the CFUUID structs byte layout until we find
        // the matching UUID bytes, we can determine the canonical size
        // of the CFRuntimeBase at runtime!
        // This is crucial since CFRuntimeBase is not guaranteed to stay
        // the same size for any given OS release, and runtime inspection is
        // necessary.

        CFUUIDRef uuidRef = CFUUIDCreate(NULL);
        CFUUIDBytes bytes = CFUUIDGetUUIDBytes(uuidRef);
        Byte *uuidBytePointerStart = (Byte *)uuidRef;
        Byte *uuidBytePointerMax = uuidBytePointerStart + (sizeof(bytes) * 2);
        for (Byte *uuidBytePointer = uuidBytePointerStart; uuidBytePointer < uuidBytePointerMax; uuidBytePointer++) {
            if (memcmp(&bytes, uuidBytePointer, sizeof(bytes)) == 0) {
                sSize = (size_t)(uuidBytePointer - uuidBytePointerStart);
                break;
            }
        }
    });

    if (!sSize) {
        NSLog(@"Could not determine the CFRuntimeBase struct size!");
    }

    return sSize;
}