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
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