[PATCH] ld: Disable separate code by default for Linux/x86

[H.J. Lu]

On Tue, Mar 17, 2026 at 5:01 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > On Mon, Mar 16, 2026 at 7:20 AM WANG Rui <r@hev.cc> wrote:
> >>
> >> Years ago, commit f6aec96dce1d ("ld: Add --enable-separate-code") introduced
> >> -z separate-code, mainly to avoid mixing code and data in the same segment
> >> for better cache performance, and enabled it by default for Linux/x86.
> >
> > -z separate-code reduces cache pollution and
>
> 64 byte section alignment would achieve the same thing, I believe.

This avoids cacheline pollution, not cache pollution.  icache can still
contain read-only data and dcache can contain code.

> But maybe there's impact on TLB slots?  But then separate-code seems to
> make page coalescing more difficult.

> > improves security by avoiding putting read-only data in the same page
> > with code.
>
> I think we've moved on from gadget avoidance as a security hardening
> approach, so I'm not sure that's relevant anymore.

So gadget isn't a security issue anymore?

> > Should ld.so map read-only data segment plus code segment into the same huge
> > page?  This should have the similar effect as -z noseparate-code.
>
> Would it?  Lots of objects have segments smaller than 2 MiB.

Does THP help their performance?  Won't  -z noseparate-code be good for them?

-- 
H.J.