Same binary code on Windows and Linux (x86)

I want to compile a bunch of C++ files into raw machine code and the run it with a platform-dependent starter written in C. Something like

fread(buffer, 1, len, file);
a=((*int(*)(int))buffer)(b);

How can I tell g++ to output raw code?

Will function calls work? How can I make it work?

I think the calling conventions of Linux and Windows differ. Is this a problem? How can I solve it?

EDIT: 开发者_运维问答I know that PE and ELF prevent the DIRECT starting of the executable. But that's what I have the starter for.

There is one (relatively) simple way of achieving some of this, and that's called "position independent code". See your compiler documentation for this.

Meaning you can compile some sources into a binary which will execute no matter where in the address space you place it. If you have such a piece of x86 binary code in a file and mmap() it (or the Windows equivalent) it is possible to invoke it from both Linux and Windows.

Limitations already mentioned are of course still present - namely, the binary code must restrict itself to using a calling convention that's identical on both platforms / can be represented on both platforms (for 32bit x86, that'd be passing args on the stack and returning values in EAX), and of course the code must be fully self-contained - no DLL function calls as resolving these is system dependent, no system calls either.

I.e.:

1. You need position-independent code
2. You must create self-contained code without any external dependencies
3. You must extract the machine code from the object file.

Then mmap() that file, initialize a function pointer, and (*myblob)(someArgs) may do.

If you're using gcc, the -ffreestanding -nostdinc -fPIC options should give you most of what you want regarding the first two, then use objdump to extract the binary blob from the ELF object file afterwards.

Theoretically, some of this is achievable. However there are so many gotchas along the way that it's not really a practical solution for anything.

• System call formats are totally incompatible
• DEP will prevent data executing as code
• Memory layouts are different
• You need to effectively dynamically 'relink' the code before you can run it.
• .. and so forth...

The same executable cannot be run on both Windows and Linux.

You write your code platform independently (STL, Boost & Qt can help with this), then compile in G++ on Linux to output a linux-binary, and similarly on a compiler on the windows platform.

EDIT: Also, perhaps these two posts might help you:

One

Two

Why don't you take a look at wine? It's for using windows executables on Linux. Another solution for that is using Java or .NET bytecode.

You can run .NET executables on Linux (requires mono runtime)

Also have a look at Agner's objconv (disassembling, converting PE executable to ELF etc.) http://www.agner.org/optimize/#objconv

Someone actually figured this out. It’s called αcτµαlly pδrταblε εxεcµταblε (APE) and you use the Cosmopolitan C library. The gist is that there’s a way to cause Windows PE executable headers to be ignored and treated as a shell script. Same goes for MacOS allowing you to define a single executable. Additionally, they also figured out how to smuggle ZIP into it so that it can incrementally compress the various sections of the file / decompress on run.

https://justine.lol/ape.html https://github.com/jart/cosmopolitan

Example of a single identical Lua binary running on Linux and Windows: https://ahgamut.github.io/2021/02/27/ape-cosmo/

Doing such a thing would be rather complicated. It isn't just a matter of the cpu commands being issued, the compiler has dependencies on many libraries that will be linked into the code. Those libraries will have to match at run-time or it won't work.

For example, the STL library is a series of templates and library functions. The compiler will inline some constructs and call the library for others. It'd have to be the exact same library to work.

Now, in theory you could avoid using any library and just write in fundamentals, but even there the compiler may make assumptions about how they work, what type of data alignment is involved, calling convention, etc.

Don't get me wrong, it can work. Look at the WINE project and other native drivers from windows being used on Linux. I'm just saying it isn't something you can quickly and easily do.

Far better would be to recompile on each platform.

That is achievable only if you have WINE available on your Linux system. Otherwise, the difference in the executable file format will prevent you from running Windows code on Linux.