Re: [PATCH] depmod: create and use System.map.no_namespaces

[Matthias Maennich]

Hi!

On Sat, Oct 05, 2019 at 04:53:56PM +0900, Masahiro Yamada wrote:
> On Sat, Oct 5, 2019 at 3:25 AM Lucas De Marchi
> <lucas.de.marchi@xxxxxxxxx> wrote:
> > On Fri, Oct 4, 2019 at 2:57 AM Matthias Maennich <maennich@xxxxxxxxxx> wrote:
> > >
> > > depmod in its current version is not aware of symbol namespace in
> > > ksymtab entries introduced with 8651ec01daed ("module: add support for
> > > symbol namespaces."). They have the form
> > >
> > >   __ksymtab_NAMESPACE.symbol_name
> > >
> > > A fix for kmod's depmod has been proposed [1]. In order to support older
> > > versions of depmod as well, create a System.map.no_namespaces during
> > > scripts/depmod.sh that has the pre-namespaces format. That way users do
> > > not immediately upgrade the userspace tool.
> > >
> > > [1] https://lore.kernel.org/linux-modules/20191004094136.166621-1-maennich@xxxxxxxxxx/
> > >
> > > Reported-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
> > > Fixes: 8651ec01daed ("module: add support for symbol namespaces.")
> > > Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> > > Cc: Lucas De Marchi <lucas.de.marchi@xxxxxxxxx>
> > > Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> > > Cc: Martijn Coenen <maco@xxxxxxxxxxx>
> > > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Cc: linux-modules@xxxxxxxxxxxxxxx
> > > Signed-off-by: Matthias Maennich <maennich@xxxxxxxxxx>
> > > ---
> > >
> > > Please note this depends on the new ksymtab entry format proposed in
> > > https://lore.kernel.org/lkml/20191003075826.7478-2-yamada.masahiro@xxxxxxxxxxxxx/
> >
> > I don't really agree with that thought, more below.
> >
> > >
> > > That is likely to be merged soon as well as it fixes problems in 5.4-rc*, hence
> > > this patch depends on it.
> > >
> > > Cheers,
> > > Matthias
> > >
> > >  .gitignore        | 1 +
> > >  scripts/depmod.sh | 8 +++++++-
> > >  2 files changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/.gitignore b/.gitignore
> > > index 70580bdd352c..5ed58a7cb433 100644
> > > --- a/.gitignore
> > > +++ b/.gitignore
> > > @@ -59,6 +59,7 @@ modules.order
> > >  /vmlinux-gdb.py
> > >  /vmlinuz
> > >  /System.map
> > > +/System.map.no_namespaces
> > >  /Module.markers
> > >  /modules.builtin.modinfo
> > >
> > > diff --git a/scripts/depmod.sh b/scripts/depmod.sh
> > > index e083bcae343f..602e1af072c7 100755
> > > --- a/scripts/depmod.sh
> > > +++ b/scripts/depmod.sh
> > > @@ -39,7 +39,13 @@ if $depmod_hack_needed; then
> > >         KERNELRELEASE=99.98.$KERNELRELEASE
> > >  fi
> > >
> > > -set -- -ae -F System.map
> > > +# Older versions of depmod do not support symbol namespaces in ksymtab entries,
> > > +# hence create an alternative System.map with namespace patched out to use for
> > > +# depmod. I.e. transform entries as follows:
> > > +#    __ksymtab_NAMESPACE.symbol_name -> __ksymtab_symbol_name
> > > +sed 's/__ksymtab_.*\./__ksymtab_/' System.map > System.map.no_namespaces
> >
> > So people with old kmod will have to know they need to pass
> > System.map.no_namespaces rather than the usual
> > System.map. Also, distros will need to be update to also copy the new
> > file to the kernel package (or upgrade/patch kmod).
> >
> > I'd rather maintain the current format and fix the bug that patch is
> > fixing. The namespace
> > in the end IMO is just a small annoyance with a reason to  exist.
>
> I agree, this fix is bad.
> We should not bother kmod or any tools.
> And System.map.no_namespaces is a cheesy workaround.

Thanks for the feedback!

Based on the discussion from last year about changing kmod/depmod for
this change to the ksymtab entries,
(https://lore.kernel.org/lkml/CAKi4VA+wvVxPxVSP6ruSR++TYvavKPNAQ5XhREF_9ZxeOKQirg@xxxxxxxxxxxxxx/),
I assumed this approach would be acceptable. The workaround (yeah, it is
a hack) is a way to mitigate the issue for people that can't update
depmod so easily. System.map.no_namespaces was not intended to be part
of any distribution, but rather used locally in depmod.sh. I could have
made this more clear.

> BTW, I expressed my negative opinion in the review process
> for the patch set. I am still not convinced with the
> namespace feature, but anyway it was merged
> (with poor review and test).
>
>
>
> Get back on track, probably the right fix would be to
> stop using __ksymtab_<namespace>.<symbol>.
>
> It is not used for any purposes but passing
> <namespace> / <symbol> pairs to modpost.
>
>
> For example, __kstrtabns_##sym points to
> the namespace string, so it would be possible
> to parse it from modpost?
>
> Then, asm("__ksymtab_" #ns NS_SEPARATOR #sym)
> will go away.

I will give this a try.

Cheers,
Matthias

> Masahiro
>
>
>
>
> > Lucas De Marchi
> >
> > > +
> > > +set -- -ae -F System.map.no_namespaces
> > >  if test -n "$INSTALL_MOD_PATH"; then
> > >         set -- "$@" -b "$INSTALL_MOD_PATH"
> > >  fi
> > > --
> > > 2.23.0.581.g78d2f28ef7-goog
> > >
> >
> >
> > --
> > Lucas De Marchi
>
>
>
> --
> Best Regards
> Masahiro Yamada