Re: [RFC PATCH v2 02/13] x86/um: nommu: elf loader for fdpic

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Tazaki-san,

On Wed, Nov 13, 2024 at 2:17 PM Hajime Tazaki <thehajime@gmail.com> wrote:
> On Wed, 13 Nov 2024 19:27:08 +0900,
> Geert Uytterhoeven wrote:
> > On Wed, Nov 13, 2024 at 9:37 AM Johannes Berg <johannes@sipsolutions.net> wrote:
> > > On Wed, 2024-11-13 at 09:36 +0100, Johannes Berg wrote:
> > > > On Wed, 2024-11-13 at 09:19 +0100, Geert Uytterhoeven wrote:
> > > > >
> > > > > > > > -       depends on ARM || ((M68K || RISCV || SUPERH || XTENSA) && !MMU)
> > > > > > > > +       depends on ARM || ((M68K || RISCV || SUPERH || UML || XTENSA) && !MMU)
> > > > > > >
> > > > > > > s/UML/X86/?
> > > > > >
> > > > > > I guess the fdpic loader can be used to X86, but this patchset only
> > > > > > adds UML to be able to select it.  I intended to add UML into nommu
> > > > > > family.
> > > > >
> > > > > While currently x86-nommu is supported for UML only, this is really
> > > > > x86-specific. I still hope UML will get support for other architectures
> > > > > one day, at which point a dependency on UML here will become wrong...
> > > > >
> > > >
> > > > X86 isn't set for UML, X64_32 and X64_64 are though.
> > > >
> > > > Given that the no-MMU UM support even is 64-bit only, that probably
> > > > should then really be (UML && X86_64).
> > > >
> > > > But it already has !MMU, so can't be selected otherwise, and it seems
> > > > that non-X86 UML
> > >
> > > ... would require far more changes in all kinds of places, so not sure
> > > I'd be too concerned about it here.
> >
> > OK, up to you...
>
> Indeed, this particular patch [02/13] intends to support the fdpic
> loader under the condition 1) x86_64 ELF binaries (w/ PIE), 2) on UML,
> 3) and with) !MMU configured.  Given that situation, the strict check
> should be like:
>
>    depends on ARM || ((M68K || RISCV || SUPERH || (UML && X86_64) || XTENSA) && !MMU)
>
> (as Johannes mentioned).
>
> on the other hand, the fdpic loader works (afaik) on MMU environment so,
>
>    depends on ARM || (UML && X86_64) || ((M68K || RISCV || SUPERH || XTENSA) && !MMU)
>
> should also works, but this might be too broad for this patchset (and
> not sure if this makes a new use case).

AFAIK that depends on the architecture's MMU context structure, cfr.
the comment in commit 782f4c5c44e7d99d ("m68knommu: allow elf_fdpic
loader to be selected"), which restricts it to nommu on m68k.  If it
does work on X86_64, you can drop the dependency on UML, and we're
(almost) back to my initial comment ;-)

> anyway, thank you for the comment.
> # I really wanted to have comments from nommu folks.

I've added some in CC...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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