const volatile behaviour change in GCC 7

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

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;

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

The corresponding GNU ld linker script section is:

    .rtemsroset : ALIGN_WITH_INPUT {
        KEEP (*(SORT(.rtemsroset.*)))
    } > REGION_RODATA AT > REGION_RODATA_LOAD

In GCC 7, the compiler deduces that "cur != end" is always true and 
generates an infinite loop.

Up to GCC 6 the "volatile const" seemed to prevent this optimization. I 
know that this linker set stuff is quite non-standard, but is there a 
way to get this to work again on GCC 7?

The nice thing with the "type volatile const X[0]..." construct is that 
you can generate arbitrary linker sets via it without a need to edit the 
linker command file and with no storage overhead.

--
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
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