Making 'long' 4 bytes in gcc on a 64-bit Linux machine

Question

I am working on porting an application to 64-bit on Linux platform. The application is currently supported on Linux, Windows, Mac 32-bit and Windows 64-bit. One of the issues we are frequently encountering is the usage of long for int and vice versa. This wasn't a problem till now since long and int are interchangeable (both are 4 bytes) in the platforms the application is currently supported on. The codebase being a huge one, with lots of legacy code with #defines for many data types, makes it cumbersome to search all usage of long and replace appropriately with int.

1. As a short term solution, is there a way to make GCC use 4 bytes instead of 8 for 'long'?
2. If it has, what are issues that we might face? If not, is there an easier way to fix the long and int problem?

Answer 1

-m32 generates 32-bit code.

-mx32 generates 64-bit code but uses 32-bit longs and pointers.

Intel 386 and AMD x86-64 Options

Answer 2

1. No. On Linux x86_64 the ABI specifies that long is a 8 byte type (LP64). In fact, most if not all 64-bit Unix systems (including 64-bit OS X, AFAIK) are LP64 so this is nothing specific to Linux.

2. Beyond fixing your code, no.

If you need a portable integer type which is large enough to store a pointer value, use intptr_t or uintptr_t (but usually wanting to store a pointer value into an integer means that you're doing something wrong, so think twice!). For an integer type which is capable of representing the difference between two pointers, use ptrdiff_t. For sizes of objects, use size_t.