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Date:      Thu, 15 Jan 2009 12:57:42 +0530
From:      Mehul Chadha <mehulc87@gmail.com>
To:        freebsd-questions@freebsd.org
Subject:   doubts regarding System Initialization working (SYSINIT)
Message-ID:  <251d650c0901142327h14387ecfn30d038fa2af7c174@mail.gmail.com>

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Hello all,
                I have been browsing through the FreeBSD kernel's source
code trying to understand its working .

In the mi_startup() in /sys/kern/init_main.c all the SYSINIT objects are
sorted using bubble sort and then they are executed in order.

My doubt is that we have declared the pointer to the struct sysinit as const
pointer to a const in the macro definition of SYSINIT ie  when the macro

SYSINIT(kmem, SI_SUB_KMEM, SI_ORDER_FIRST, kmeminit, NULL)  is expanded
completely we get the following

static struct sysinit kmem_sys_init = { SI_SUB_KMEM, SI_ORDER_FIRST,
(sysinit_cfunc_t)(sysinit_nfunc_t)kmeminit, ((void *)(((void *)0))) };
static void const * const __set_sysinit_set_sym_kmem_sys_init
__attribute__((__section__("set_" "sysinit_set"))) __attribute__((__used__))
= &kmem_sys_init;

Here we see that the pointer is of type const and to a const but when we
sort
and swap using
                              *sipp=*xipp;

We are trying to change the address of const pointer to a new address in
which case it should segfault but it works fine.

Why does it not segfault it seems I have not understood the concept behind
using const *const... I will be very thankful if you can help me with it.


Regards,
Mehul



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