Re: [PATCH] elf: dl-minimal malloc needs to respect fundamental alignment

[Florian Weimer <fweimer at redhat dot com>]

On 06/21/2016 02:54 PM, H.J. Lu wrote:
> On Tue, Jun 21, 2016 at 4:17 AM, Florian Weimer <fweimer@redhat.com> wrote:
> > If malloc is used instead of memalign for small alignments,
> > malloc needs to provide the ABI-required alignment.
> >
> > 2016-06-21  Florian Weimer  <fweimer@redhat.com>
> >
> >         * elf/dl-minimal.c (malloc): Allocate with fundamental alignment.
> >
> > diff --git a/elf/dl-minimal.c b/elf/dl-minimal.c
> > index c8a8f8d..2d7d139 100644
> > --- a/elf/dl-minimal.c
> > +++ b/elf/dl-minimal.c
> > @@ -27,6 +27,7 @@
> >  #include <sys/types.h>
> >  #include <ldsodefs.h>
> >  #include <_itoa.h>
> > +#include <stdalign.h>
> >
> >  #include <assert.h>
> >
> > @@ -90,7 +91,7 @@ __libc_memalign (size_t align, size_t n)
> >  void * weak_function
> >  malloc (size_t n)
> >  {
> > -  return __libc_memalign (sizeof (double), n);
> > +  return __libc_memalign (_Alignof (max_align_t), n);
> >  }
> >
> >  /* We use this function occasionally since the real implementation may
>
> We also have MALLOC_ALIGNMENT in malloc.  Should they be consistent?

MALLOC_ALIGNMENT is potentially larger.  malloc/tst-malloc-thread-fail 
tests for alignment.  To my knowledge, it passes on all regularly tested 
architectures after commit dea39b13e2958a7f0e75b5594a06d97d61cc439f.

Thanks,
Florian