ELF LOAD segments creating holes in the process image on GNU/Linux

[H.J. Lu]

On Mon, Jan 3, 2022 at 4:49 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > On Mon, Jan 3, 2022 at 4:31 AM Florian Weimer via Binutils
> > <binutils@sourceware.org> wrote:
> >>
> >> At least on x86-64 on GNU/Linux, for PIE and non-PIE binaries, LOAD
> >> segments are not always contiguous.  The triggering conditions are not
> >> quite clear to me.
> >>
> >> For ET_EXEC (non-PIE) executables, I think this is a supported feature,
> >> and the kernel and glibc dynamic loader handle this the same way,
> >> creating holes.  However, these holes make dealing with the main
> >> executable slightly more complicated in some cases (e.g., we can handle
> >> contiguous mapping slightly more efficiently when looking objects based
> >> on addresses).  Holes also make page tables less compact (although that
> >> effect is probably minuscule).  Abstractly, I don't see a reason why the
> >> link editor has to create such holes on the most common targets.  (I
> >> have heard that ia64 really needed those holes.)
> >>
> >> For ET_DYN (PIE) executables, we have a Linux vs glibc difference: The
> >> Linux loader creates holes as well, while the glibc loader refuses to
> >> create them and fills them with a PROT_NONE mapping from the executable.
> >>
> >> Is this something we could fix in ld?
> >>
> >
> > Is it created by -z separate-code?
>
> I believe so because it is the default?
>

What do you want linker to do?

-- 
H.J.