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From: Sascha Hauer <s.hauer@pengutronix.de>
To: Franck Jullien <franck.jullien@gmail.com>
Cc: barebox <barebox@lists.infradead.org>
Subject: Re: GCC question
Date: Wed, 9 Jan 2013 10:09:13 +0100	[thread overview]
Message-ID: <20130109090913.GR1906@pengutronix.de> (raw)
In-Reply-To: <CAJfOKBzoXNvQu38qXXu9w9fyBuWqC_kAmHUqw2Z5B=8d9ymejg@mail.gmail.com>

On Wed, Jan 09, 2013 at 10:02:32AM +0100, Franck Jullien wrote:
> Hi,
> 
> I have a question not directly related to Barebox but I think I can
> find some answer here: )
> 
> I would like to use initcalls in a Linux user's land program on a x86 target.
> 
> I'm doing something like this:
> 
> #ifndef _INIT_H
> #define _INIT_H
> 
> typedef int (*initcall_t)(void);
> 
> extern initcall_t __start_target, __stop_target;
> 
> #define target_initcall(fn)	static initcall_t _##fn \
> 				__attribute__((used)) \
> 				__attribute__ ((section("target"))) = fn
> 
> #endif
> 
> then:
> 
> 	initcall_t *initcall;
> 
> 	for (initcall = &__start_target;
> 			initcall < &__stop_target; initcall++) {
> 		printf("initcall-> %p\n", *initcall);
> 		ret = (*initcall)();
> 		if (ret)
> 			printf("initcall %p failed: %d\n", *initcall, ret);
> 	}
> 
> Everything looks fine except the linker removes the function
> "initcalled" because it is not
> referenced anywhere and this is normal.
> 
> I have not modified the linker script (I'm using the default one). I'm
> using auto generated
> __start_target and __stop_target symbols generated by the linker.
> 
> My question is: why does it work in barebox ? For example, in
> nios2/generic.c we have only
> static function and initcalls. So why the linker does optimize out
> those functions ? Is it
> because we have initcall corresponding sections in the linker script ?

Yes. In nios2 this is:

	__barebox_initcalls_start = .;
	.barebox_initcalls : { INITCALLS }
	__barebox_initcalls_end = .;

With INITCALLS being defined as:

#define INITCALLS			\
	KEEP(*(.initcall.0))			\
	KEEP(*(.initcall.1))			\
	KEEP(*(.initcall.2))			\
	KEEP(*(.initcall.3))			\
	KEEP(*(.initcall.4))			\
	KEEP(*(.initcall.5))			\
	KEEP(*(.initcall.6))			\
	KEEP(*(.initcall.7))			\
	KEEP(*(.initcall.8))			\
	KEEP(*(.initcall.9))			\
	KEEP(*(.initcall.10))			\
	KEEP(*(.initcall.11))

The 'KEEP' keyword keeps the linker from throwing away these.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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  reply	other threads:[~2013-01-09  9:09 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-09  9:02 Franck Jullien
2013-01-09  9:09 ` Sascha Hauer [this message]
2013-01-09  9:13   ` Franck Jullien
2013-01-09  9:28     ` Sascha Hauer
2013-01-10 12:36 ` Jean-Christophe PLAGNIOL-VILLARD
2013-01-10 12:52   ` Franck Jullien

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