On Tue, 2012-07-17 at 02:03 +0700, Mulyadi Santosa wrote:
Hi :)
On Tue, Jul 17, 2012 at 1:49 AM, Aft nix <aftnix@gmail.com> wrote:
This special section, "data..read_mostly" , is it maintained by kernel?
by maintained, you mean allocated? then yes....
then Linker has to know this information. How that is done?
it is provided by the linker script.... the fastest I can find is in directory include/asm-generic/vmlinux.lds.h. This file is not final linker script, it's kinda a "template" that will be further modified by Kbuild (I guess)
I mean lets say a.c is compiled into a.o. a.o already has the offsets for its data. Linker resolves the final address. So how the linker is invoked in a way so that this data flagged with __read__mostly will end up in the special section?
it's actually the same like putting your initialized variable in .data section, your code in .text and so on. I just get the big picture that it is done by creating section in the object file. By section, I think it's simply done by creating a mark to denote the section.
please kindly study ELF documentation for further info
Thing is, i'm getting the idea what these macros mean, but not understanding the mechanisms behind them.
the whole chain is complex actually, but try to get the simple view first. it's a grouping, read mostly data into a section/group in a file (in this case, kernel image), kernel loaded.....kernel arrange itself..put appropriate section into related addresses....done
Thanks for the detailed explanation. I've got the idea behind __read_mostly. I've found a interesting document "Dead code elimination " which i guess relates to "__init" and "__exit". Here is the link : elinux.org/images/2/2d/ELC2010-gc-sections_Denys_Vlasenko.pdf I'm going to study this post if any question arises. cheers.