[PATCH v2] elf: Set p_align to the minimum page size if possible

[Alan Modra]

On Fri, Dec 24, 2021 at 06:50:30PM -0800, H.J. Lu wrote:
> On Fri, Dec 24, 2021 at 5:03 PM Alan Modra <amodra@gmail.com> wrote:
> > I don't see a way to change DT_LOAD p_align that is backwards
> > compatible, except perhaps using a p_align of zero if the required
> > segment alignment (as calculated from section alignment) is less than
> > maxpagesize.  That horrible hack just happens to work for older glibc,
> > but may break other loaders.
> 
> Neither 0 nor 1 work for older glibc:
> 
>           if (__glibc_unlikely ((ph->p_align & (GLRO(dl_pagesize) - 1)) != 0))
>             {
>               errstring = N_("ELF load command alignment not page-aligned");
>               goto lose;
>             }
>           if (__glibc_unlikely (((ph->p_vaddr - ph->p_offset)
>                                  & (ph->p_align - 1)) != 0))
>             {
>               errstring
>                 = N_("ELF load command address/offset not properly aligned");
>               goto lose;
>             }

Zero in p_align triggers neither of these conditions.  Binaries with
zero p_align run.  I checked.

-- 
Alan Modra
Australia Development Lab, IBM