Re: [Tinycc-devel] OSX

[Peter \"Firefly\" Lund]

On Sun, 20 Apr 2003, Steve Dekorte wrote:

> > 2) Do you know the executable format for OS X?  Does it use ELF?  COFF?
>
> Mach-O, I think. I don't know anything about executable formats, btw.
> This sounds difficult...

After a little googling I can confirm that it uses Mach-O :(

It is apparently also possible to load and execute a few other file
formats, one of them being ELF -- but you may need to cast a few spells
first.  (This is not all that different from FreeBSD being able to run
Linux binaries and Linux being able to run Java, MS-DOS exe files, and
Windows binaries seamlessly, provided the right wrappers are installed)

Mach-O seems to be a sensible format so it is not so bad as it might first
look.

Since you are only interested in compilation to memory, you can cheat a
little.  Stub out the ELF calls to make tcc generate raw binaries which
you can then disassemble (with objdump if with nothing else).  You can
also run tcc in a debugger and see "live" what code it generates but it is
hard to do regression tests with a human in the loop ;)

You will also need to insert either instructions or OS X calls to handle
the run-time code generation (cache flushing/invalidation, perhaps also
TLB flushing/invalidation) + you might need mprotect() or similar to tell
OS X that the piece of memory you are generating code into should be
marked executable.

Considering this, I definitely think it would be easier to just generate
raw binary files (without symbols or relocation tables) at first.

-Peter

"Of course, I'm not unbiased, but in my humble opinion, I've
 gotten close to something that I can be really proud of."
 -- Knuth on The Art of Computer Programming.