Re: GCC question

[Franck Jullien <franck.jullien@gmail.com>]

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.                           |                             |
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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.

Franck.

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