Re: [PATCH] Fix tst-array* on x86_64

[Jakub Jelinek <jakub at redhat dot com>]

On Tue, Dec 10, 2002 at 09:43:08AM -0800, H. J. Lu wrote:
> On Tue, Dec 10, 2002 at 02:52:50PM +0100, Jakub Jelinek wrote:
> > Hi!
> > 
> > This is actually the same crap as I had to work around in test-string.h,
> > ie. x86_64 aligns preinit_array etc. to 16 bytes because they are >=
> > 16 bytes, yet its actual size is 24 bytes.
> >   /* x86-64 ABI requires arrays greater than 16 bytes to be aligned
> >      to 16byte boundary.  */
> > Linker script of course doesn't expect .init_array/.fini_array/.preinit_array
> > sections to be more than word aligned and thus the labels around them
> > are on wrong positions.
> > 
> > 2002-12-10  Jakub Jelinek  <jakub@redhat.com>
> > 
> > 	* elf/tst-array1.c (preinit_array, init_array, fini_array):
> > 	Explicitely align the array to sizeof (void *).
> > 	* elf/tst-array2dep.c (init_array, fini_array): Likewise.
> > 
> > --- libc/elf/tst-array1.c.jj	2002-11-07 23:28:04.000000000 +0100
> > +++ libc/elf/tst-array1.c	2002-12-10 16:01:54.000000000 +0100
> > @@ -35,7 +35,7 @@ preinit_2 (void)
> >  }
> >  
> >  void (*const preinit_array []) (void)
> > -     __attribute__ ((section (".preinit_array"))) =
> > +     __attribute__ ((section (".preinit_array"), aligned (sizeof (void *)))) =
> >  {
> >    &preinit_0,
> >    &preinit_1,
> 
> I assume size of void * is 8 byte for x86_64. Will it align at 16 byte?

Yes. It will align that way any array whose entries are aligned to <= 16 bytes
and whose size is >= 16 bytes.
E.g. if:
void (*const preinit_array_0) (void) __attribute__ ((section (".preinit_array"))) = &preinit_0;
void (*const preinit_array_1) (void) __attribute__ ((section (".preinit_array"))) = &preinit_1;
void (*const preinit_array_2) (void) __attribute__ ((section (".preinit_array"))) = &preinit_2;
was used instead, it would be just 8 aligned.

> Those *_array sections are special sections. Should they be handled by
> gas/ld automatically?

It is gcc's problem (and in this case testcase writer's problem) to follow
the rules.

	Jakub