Re: rs_init()

[Erik Mouw <J.A.K.Mouw@ITS.TUDelft.NL>]

On Mon, Oct 08, 2001 at 12:39:57PM -0700, Manoj Ekbote wrote:

Please fix your mailer so it will break lines at 72 characters. Makes
your messages much more readable.

> I have been looking at the linux serial driver initialization routine
> rs_init() in drivers/char/serial.c. This routine gets invoked as a
> part of a do-while loop in do_initcalls() in init/main.c.The code
> looks something like this:
> 
> static void __init do_initcalls(void)
> {
>         initcall_t *call;
> 
>         call = &__initcall_start;
>         do {
>                 (*call)();
>                 call++;
>         } while (call < &__initcall_end);
> 
>         /* Make sure there is no pending stuff from the initcall sequence */
>         flush_scheduled_tasks();
> }
> 
> I would like to know where exactly is rs_init() being inserted into
> the chain of routines that gets invoked in the do-while loop.

Welcome to linker magic!

The __initcall directive expands to something like __attribute__
((unused,__section__ (".initcall.init"))), which will instruct the
compiler to but the function pointer in the .initcall.init ELF section
(see gcc info file for more information). The boundaries of this
section are __initcall_start and __initcall_end, also filled in by the
linker at link time.

So the rs_init() function pointer will be put *somewhere* into the
.initcall.init section. At boot, the function do_initcalls() will call
all function pointers in the section, so at a certain point rs_init()
will also be called through its function pointer in the .initcall.init
section.


Erik

-- 
J.A.K. (Erik) Mouw, Information and Communication Theory Group, Department
of Electrical Engineering, Faculty of Information Technology and Systems,
Delft University of Technology, PO BOX 5031,  2600 GA Delft, The Netherlands
Phone: +31-15-2783635  Fax: +31-15-2781843  Email: J.A.K.Mouw@its.tudelft.nl
WWW: http://www-ict.its.tudelft.nl/~erik/
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