How to convert 32-bit compiled binary to 64-bit [closed]

Question

Background: We have acquired a software product that builds to a 32-bit Windows application in Visual Studio. We wish to port this application to 64-bit.

A mission-critical component of this code is a black-box static library (.a file) originally built using gFortran by a third party. The original developer has since passed away, and the Fortran source we were able to get was incomplete and not the version this library was built off of (and contains critical bugs not present in the compiled library). They did not use a VCS.

Problem: I would like to create a 64-bit static library whose code is functionally equivalent to the 32-bit static library we have.

What I've Tried:

• Using the Snowman decompiler to get C++ source code to recompile in 64-bit. This proved impossible because the code that was generated uses low-level intrinsic functions that appear to be gcc-specific. It likely wouldn't work anyway because such intrinsics would compile to code that isn't functionally equivalent in 64-bit. I'd likely need a better decompiler.
• Apparently x86 assembly is valid x86_64 assembly, so I looked briefly into why I couldn't just run the assembly through a 64-bit assembler. Turns out the ABI is different in 64-bit, so the calling convention won't match. MAYBE I could manually convert the function calls to the proper convention and leave the rest the same, but that might be an intractable problem. Opinions?

Answer 1

You could keep the 32-bit binary library but load it into a 32-bit host process, and use some kind of IPC (shared memory, named pipes, local-loopback network connection, etc) to transfer data to/from your 64-bit process.

Another advantage to this approach is that if the Fortran code crashes then it will only bring down the child host process, not your main application and your program can instantly fire it up again; and if it's a single-threaded Fortran program then you could spin up several instances for multi-core parallelism.