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    SubjectRe: Kernel Development & Objective-C
    On Fri, 30 Nov 2007 11:29:55 +0100, "Loïc Grenié" <> wrote:

    > 2007/11/29, Ben Crowhurst <>:
    > > Has Objective-C ever been considered for kernel development?
    > >
    > > regards,
    > > BPC

    Well, I really would like to learn some things here, could we
    keep this off-topic thread alive just a bit, please ?
    (I know, I'm going to gain a troll's fame because I can't avoid this
    discussions, its one of my secret vices...)

    > No, it has not. Any language that looks remotely like an OO language
    > has not ever been considered for (Linux) kernel development and for
    > most, if not all, other operating systems kernels.

    I think BeOS was C++ and OSX is C+ObjectiveC (and runs on an iPhone).
    Original MacOS (fron 6 to 9) was Pascal (and a mac SE was very near
    to embedded hardware :) ).

    I do not advocate to rewrite Linux in C++, but don't say a kernel written
    in C++ can not be efficient.

    > Various problems occur in an object oriented language. One of them
    > is garbage collection: it provokes asynchronous delays and, during
    > an interrupt or a system call for a real time task, the kernel cannot
    > wait.

    C++ (and for what I read on other answer, nor ObjectiveC) has no garbage
    collection. It does not anything you did not it to do. It just allows
    you to change this

    struct buffer *x;
    x = kmalloc(...)
    x->sz = 128
    x->buff = kmalloc(...)

    struct buffer *x;
    x = new buffer(128); (that does itself allocates x->buff,
    because _you_ programmed it,
    so you poor programmer don't forget)
    delete x; (that also was programmed to deallocate
    x->buff itself, sou you have one less
    memory leak to worry about)

    > Another is memory overhead: all the magic that OO languages
    > provide take space in memory and Linux kernel is used in embedded
    > systems with very tight memory requirements.

    An vtable in C++ takes exactly the same space that the function
    table pointer present in every driver nowadays... and probably
    the virtual method call that C++ does itself with


    push thing
    push with
    push this
    call THING_vtable+indexof(do_something) // constants at compile time

    is much more efficient that what gcc can mangle to do with


    push with
    push this
    push thing
    get thing+offsetof(do_something) // not constant at compile time
    dereference it
    call it

    (that is, get a generic field on a structure and use it as jump address)

    In short, the kernel is object oriented, implements OO programming by
    hand, but the compiler lacks the knowledge that it is object oriented
    programming so it could do some optimizations.

    > Lots of people will think of better reasons why ObjC is not used...

    People usually complains about RTTI or exceptions, but benefits versus
    memory space should be seriously considered (sure there is something
    in current drivers to ask 'are you a SATA or an IDE disk?').

    J.A. Magallon <jamagallon()ono!com> \ Software is like sex:
    \ It's better when it's free
    Mandriva Linux release 2008.1 (Cooker) for i586
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