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Re: const volatile behaviour change in GCC 7


Sebastian Huber <sebastian.huber@embedded-brains.de> writes:
> Hello,
>
> for RTEMS we use linker sets to initialize the system. The following
> code worked up to GCC 6, but no longer in GCC 7:
>
> typedef void ( *rtems_sysinit_handler )( void );
>
> typedef struct {
>   rtems_sysinit_handler handler;
> } rtems_sysinit_item;
>
> rtems_sysinit_item volatile const _Linker_set__Sysinit_begin[0]
> __attribute__((__section__(".rtemsroset." "_Sysinit" ".begin")))
> __attribute__((__used__));
>
> rtems_sysinit_item volatile const _Linker_set__Sysinit_end[0]
> __attribute__((__section__(".rtemsroset." "_Sysinit" ".end")))
> __attribute__((__used__));
>
> void rtems_initialize_executive(void)
> {
>   const volatile rtems_sysinit_item *cur = _Linker_set__Sysinit_begin;
>   const volatile rtems_sysinit_item *end = _Linker_set__Sysinit_end;

You likely have 'volatile' in a wrong place. Try (untested):

rtems_sysinit_item const _Linker_set__Sysinit_begin[0]
__attribute__((__section__(".rtemsroset." "_Sysinit" ".begin")))
__attribute__((__used__));

rtems_sysinit_item const _Linker_set__Sysinit_end[0]
__attribute__((__section__(".rtemsroset." "_Sysinit" ".end")))
__attribute__((__used__));

void rtems_initialize_executive(void)
{
  rtems_sysinit_item const *volatile cur = _Linker_set__Sysinit_begin;
  rtems_sysinit_item const *volatile end = _Linker_set__Sysinit_end;

  while(cur != end) {
    cur->handler();
    ++cur;
  }
}

Alternatively, try (untested, and I removed attributes to make my point
clearer): 

/* Linker-defined symbols */

rtems_sysinit_item const _Linker_set__Sysinit_begin[0]
__attribute__((__section__(".rtemsroset." "_Sysinit" ".begin")))
__attribute__((__used__));

rtems_sysinit_item const _Linker_set__Sysinit_end[0]
__attribute__((__section__(".rtemsroset." "_Sysinit" ".end")))
__attribute__((__used__));

/* Get volatile pointers to the above */
static rtems_sysinit_item const *volatile begin_ = _Linker_set__Sysinit_begin;
static rtems_sysinit_item const *volatile end_   = _Linker_set__Sysinit_end;

void rtems_initialize_executive(void)
{
  rtems_sysinit_item const *cur = begin_;
  rtems_sysinit_item const *end = end_;

  while(cur != end) {
    cur->handler();
    ++cur;
  }
}

HTH

-- Sergey


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