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

[Florian Weimer]

* 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?

Thanks,
Florian