Can I link object files made by one compile to those made by another one?

Question

To be more specific, lets assume that both compilers are on the same platform (OS + instruction set). However, one of the object files was made from a compiler-dependent code. On the other hand - the code is object oriented and respects encapsulation.

I need this for a kind of a framework I am making. Target platform is any system where is GCC and Java Virtual Machine. Indeed the framework will be compiled on each platform. The compiler which use the framework user is up to him.

Answer 1

You should be able to link them as long as they use the same object file format and target the same machine instruction set. For example, say you have two C compilers each with it's own proprietary language extensions. You compile two different files, one with compiler A the other with compiler B. Each source file uses language extensions of it's respective compiler. As long as both compilers are set to target the same platform and architecture, for example i386 instruction set on Linux, then you should be able to link the files into one executable.

See this list of object file formats on wiki.

This might also be of interest to you:

UNIX tools for exploring object files

EDIT

According to this article, "C++ Standard Library ABI", there is an industry standard C++ ABI and you should be able to link objects files of any compiler which conforms to this standard. You can see that standard here:

Itanium C++ ABI

This document was developed jointly by an informal industry coalition consisting of (in alphabetical order) CodeSourcery, Compaq, EDG, HP, IBM, Intel, Red Hat, and SGI...

In this document, we specify the Application Binary Interface for C++ programs, that is, the object code interfaces between user C++ code and the implementation-provided system and libraries. This includes the memory layout for C++ data objects, including both predefined and user-defined data types, as well as internal compiler generated objects such as virtual tables. It also includes function calling interfaces, exception handling interfaces, global naming, and various object code conventions.

So as long as you target the same instruction set, object file format and use the standard C++ ABI ( which is now the default in gcc / g++ ) you should be ok, assuming of course that the standard C++ ABI is actually standard and properly implemented by most modern C++ compilers that run on Linux ( which seems to be the platform you're targeting ).

EDIT 2

You should take a look at this SO post:

GCC vs MS C++ compiler for maintaining API backwards binary compatibility

It seems like Microsoft doesn't follow any consistent standard ( Itanium or otherwise ) regarding their C++ ABI, so if you compile with gcc for Windows it likely is going to be a problem.

You probably also want to look at these two articles:

Policies/Binary Compatibility Issues With C++

Some thoughts on binary compatibility

You could restrict your users to compilers which support the Itanium ABI, but that depends on your target audience.

Answer 2

It depends on the compilers. Some are using the same ABI and thus generate objects which can be linked together, some don't and the objects can't be linked. Usually -- in fact, I know of no exception -- when compilers are using incompatible ABI, they are also using incompatible name mangling and the link phase fails.

In fact, one need quite a lot of effort and concertation for being able to link together objects built with different compilers. There was a time when often it wasn't possible between two different versions of gcc.

There is quite a lot more in the ABI than the name mangling:

• precise layout of objects (included padding, the format of the vtable and the format of RTTI info,...)

• the way exceptions are carried on

• the way results are returned

• the way parameters are passed (in registers or not, which registers, where is this)

• who save the registers which don't are used for result/parameter (the caller, the callee, ...)

• the way templates are handled (static data members for instance)

• the standard library version used

• ...

To give an idea of the complexity of an ABI, here is a document which describes in details the ABI used on Itanium. IIRC, it is an addition over a similar document describing the C ABI. It is used (for the non machine dependent parts) by gcc on other targets.