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

[Hajime Tazaki]

Hello,

thanks for the inputs Geert, Johannes,

On Wed, 13 Nov 2024 19:27:08 +0900,
Geert Uytterhoeven wrote:
> 
> Hi Johannes,
> 
> On Wed, Nov 13, 2024 at 9:37 AM Johannes Berg <johannes at 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).

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

-- Hajime