Re: [RFC PATCH 0/6] fix nommu mmap and add nommu kselftests

Hi Hajime,

On Sat, 15 Aug 2026 at 00:28, Hajime Tazaki <[email protected]> wrote:
> On Fri, 14 Aug 2026 20:24:57 +0900,
> Lorenzo Stoakes (ARM) wrote:
> > vfork() has entirely different semantics than fork() and we need to assert
> > fork() behaviour, not vfork() behaviour.
> >
> > (Honestly it's completely bizarre that we support a version of linux that
> > can't fork() in 2026)
>
> I understand your concern on fork-less kernel.
>
> I am aware of some of experimental work which try to introduce fork(2)
> (or alike) features into nommu (or alike) kernels (links below).  some
> of them require a CPU features, some of them gave up CoW, etc.  I
> haven't really look into details but if these effort contain a
> meaningful insight to implement in Linux mainline, I would spend more
> time to study these in order to fill the current gaps between current
> MMU and !MMU.

You could implement fork(), if you teach the userspace compiler to do
all addressing relative to a few base registers (PC-relative for text,
other bases for data, bss, stack, and heap).  Then fork() becomes an
(expensive) copy of all but read-only text, and adjusting the base
registers.

Of course there would still be no memory protection, so user space
can still do whatever it wants...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds