Really a very informative and interesting thread.
Thank you all for your efforts.
Rgds,
Adil
On 3/16/08, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote:
Thank you everyone for the time spent in the analysis. I understand
better now.
I was confused, as I thought the module_free() below actually free up
the entire module. But as you and Johannes and etc have highlighted,
module_free() only free up the INIT section:
mutex_lock(&module_mutex);
/* Drop initial reference. */
module_put(mod);
unwind_remove_table(mod->unwind_info, 1);
module_free(mod, mod->module_init);
mod->module_init = NULL;
mod->init_size = 0;
mod->init_text_size = 0;
mutex_unlock(&module_mutex);
Apologized for the confusion!!!! Thanks :-).
On Sun, Mar 16, 2008 at 1:22 AM, Thomas Petazzoni
<thomas.petazzoni@xxxxxxxxxxxxxxxxxx> wrote:
> Hi,
>
> Le Sun, 16 Mar 2008 00:57:00 +0800,
> "Peter Teoh" <htmldeveloper@xxxxxxxxx> a écrit :
>
>
> > may be....where is it?? i will continue the search....thank you for
> > the feedback.
>
> Everything starts in sys_init_module()
> http://lxr.free-electrons.com/source/kernel/module.c#2090
>
> It starts by loading the module using load_module()
> http://lxr.free-electrons.com/source/kernel/module.c#1650
>
> Which at some points, calls layout_sections(), which computes
> mod->init_size:
>
> 1487 for (m = 0; m < ARRAY_SIZE(masks); ++m) {
> 1488 for (i = 0; i < hdr->e_shnum; ++i) {
> 1489 Elf_Shdr *s = &sechdrs[i];
> 1490
> 1491 if ((s->sh_flags & masks[m][0]) != masks[m][0]
> 1492 || (s->sh_flags & masks[m][1])
> 1493 || s->sh_entsize != ~0UL
> 1494 || strncmp(secstrings + s->sh_name,
> 1495 ".init", 5) != 0)
> 1496 continue;
> 1497 s->sh_entsize = (get_offset(&mod->init_size, s)
> 1498 | INIT_OFFSET_MASK);
> 1499 DEBUGP("\t%s\n", secstrings + s->sh_name);
> 1500 }
> 1501 if (m == 0)
> 1502 mod->init_text_size = mod->init_size;
> 1503 }
>
> This loop has the effect of adding in mod->init_size the size of all
> ELF sections whose name starts with .init. So in load_module(), after
> the call to layout_sections(), mod->init_size is the size of .init.text
> + init.data + others .init sections.
>
> Back in load_module(), it does:
>
> 1852 ptr = module_alloc(mod->init_size);
> 1853 if (!ptr && mod->init_size) {
> 1854 err = -ENOMEM;
> 1855 goto free_core;
> 1856 }
> 1857 memset(ptr, 0, mod->init_size);
> 1858 mod->module_init = ptr;
>
> So it allocates a specific memory area for init code and data, which is
> pointed by mod->module_init.
>
> Then, if you look back in sys_init_module(), you see that the init
> function of the module is called:
>
> 2125 if (mod->init != NULL)
> 2126 ret = mod->init();
>
> And if everything went right during the initialization, the following
> line is executed:
>
> 2145 module_free(mod, mod->module_init);
>
> Which frees the init code and data.
>
>
>
> Sincerly,
>
> Thomas
> --
> Thomas Petazzoni, Free Electrons
> Free Embedded Linux Training Materials
> on http://free-electrons.com/training
> (More than 1500 pages!)
>
--
Regards,
Peter Teoh
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