Re: GCC question

[Sascha Hauer <s.hauer@pengutronix.de>]

On Wed, Jan 09, 2013 at 10:13:51AM +0100, Franck Jullien wrote:
> 2013/1/9 Sascha Hauer <s.hauer@pengutronix.de>:
> > 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/  |
> > Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
> > Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
> 
> Thanks Sascha, I missed this one.....
> 
> So is there no way I can do what I want without modification to the
> default linker script.
> I searched for a gcc attibute equivalent to KEEP but it doesn't seems to exist.

No, and this wouldn't be enough anyway. You also have to tell the linker
that it shall put all functions matching .initcall.* in a separate
section. Otherwise they would end up in the regular sections.

Sascha


-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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