Re: Kernel Development & Objective-C

Kyle Moffett
2007-11-30T15:26:28Z

On Nov 30, 2007, at 09:34:45, Lennart Sorensen wrote:
> On Thu, Nov 29, 2007 at 12:14:16PM +0000, Ben Crowhurst wrote:
>> Has Objective-C ever been considered for kernel development?
>
> Doesn't objective C essentially require a runtime to provide a lot
> of the features of the language? If it does (as I suspect) then it
> is totally unsiatable for kernel development.
>
> That and object oriented languages in general are badly designed
> and a bad idea. Having not used objective C I have no idea if it
> qualifies as badly designed or not. Certainly C++ and java are
> both very badly designed.

Objective-C is actually a pretty minimal wrapper around C; it was
originally implemented as a C preprocessor. It generally does not
have any kind of memory management, garbage collection, or anything
else (although typically a "runtime" will provide those features).
There are no first-class exceptions, so there would be nothing to
worry about there (the exceptions used in GUI programs are built
around the setjmp/longjmp primitives). Objective-C is also almost
completely backwards-compatible with C, much more so than C++ ever
was. As far as the runtime goes the kernel would be expected to
write its own, the same way that it implements "kmalloc()" as part of
a "C runtime". Since the runtime itself never does any implicit
memory allocation, I think it would conceivably even be relatively
safe for kernel usage.

With that said, there is a significant performance penalty as all
Objective-C method calls are looked up symbolically at runtime for
every single call. For GUI programs where large chunks of the code
are event-loops and not performance-sensitive that provides a huge
amount of extra flexibility. In the kernel though, there are many
codepaths where *every* *single* instruction counts; that could be a
serious performance hit.

Cheers,
Kyle Moffett