Re: [PATCH] binfmt_flat: Remove shared library support

[Rich Felker <dalias@libc.org>]

On Thu, Apr 21, 2022 at 08:52:59AM +0200, Geert Uytterhoeven wrote:
> On Thu, Apr 21, 2022 at 1:53 AM Greg Ungerer <gerg@linux-m68k.org> wrote:
> > On 21/4/22 00:58, Eric W. Biederman wrote:
> > > In a recent discussion[1] it was reported that the binfmt_flat library
> > > support was only ever used on m68k and even on m68k has not been used
> > > in a very long time.
> > >
> > > The structure of binfmt_flat is different from all of the other binfmt
> > > implementations becasue of this shared library support and it made
> > > life and code review more effort when I refactored the code in fs/exec.c.
> > >
> > > Since in practice the code is dead remove the binfmt_flat shared libarary
> > > support and make maintenance of the code easier.
> > >
> > > [1] https://lkml.kernel.org/r/81788b56-5b15-7308-38c7-c7f2502c4e15@linux-m68k.org
> > > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> > > ---
> > >
> > > Can the binfmt_flat folks please verify that the shared library support
> > > really isn't used?
> >
> > I can definitely confirm I don't use it on m68k. And I don't know of
> > anyone that has used it in many years.
> >
> >
> > > Was binfmt_flat being enabled on arm and sh the mistake it looks like?
> 
> I think the question was intended to be
> 
>     Was *binfmt_flat_shared_flat* being enabled on arm and sh the
>     mistake it looks like?

Early in my work on j2, I tried to research the history of shared flat
support on sh, and it turned out the mainline tooling never even
supported it, and the out-of-line tooling I eventually found was using
all sorts of wrong conditionals for how it did the linking and elf2flt
conversion, e.g. mere presence of any PIC-like relocation in any file
made it assume the whole program was PIC-compatible. There's no way
that stuf was ever used in any meaningful way. It just didn't work.

Quickly dropped that and got plain ELF (no shared text/xip, but no
worse than the existing flat support) working, and soon after, FDPIC.

The whole binfmt_flat ecosystem is a mess with no good reason to
exist.

Rich