Force LP64 data model with GCC or Clang in Windows

Question

Is there a way to force GCC and/or Clang compiler to use LP64 data model when targeting Windows (ignoring that Windows use LLP64 data model)?

Answer 1

No, because the requested capability would not work

You are "targeting Windows", presumably meaning you want the compiler to produce code that will run under Windows in the usual way. In order to do that, the program must invoke functions in the Windows API. There are effectively three versions of the Windows API: win16, win32, and win64. Since you want 64-bit pointers (the "P64" in "LP64"), the only possible target is win64.

In order to call a win64 function, you must include windows.h. That header file uses long. If there were a compiler switch to insist that long be treated as a 64-bit integer (LP64) rather than 32-bit (LLP64), then the compiler's understanding of how to call functions and lay out data structures that use long would be wrong; the resulting program would not run correctly.

The same problem applies to the standard C and C++ libraries. If you link to an existing compiled library (as is typical), the calls into it won't work (since it will use LLP64). If you were to build one from source using a hypothetical switch to force LP64, its calls into the Windows API would fail.

But you can try Cygwin

Cygwin uses LP64 and produces binaries that run on Windows. That is possible, despite what I wrote above, because the Cygwin DLL acts as a bridge between the Cygwin LP64 environment and the native win64 LLP64 environment. Assuming you have code originally written for win32 that you now want to take advantage of a 64-bit address space with no or minimal code changes, I suspect this is the easiest path. But I should acknowledge that I've never used Cygwin in quite this way so there might be problems I am not aware of.