Re: [PATCH v2] scripts: Exclude Rust CUs with pahole

[Eric Curtin <ecurtin@redhat.com>]

On Sun, 8 Jan 2023 at 15:18, Eric Curtin <ecurtin@redhat.com> wrote:
>
> On Sun, 8 Jan 2023 at 02:15, Martin Rodriguez Reboredo
> <yakoyoku@gmail.com> wrote:
> >
> > Version 1.24 of pahole has the capability to exclude compilation units
> > (CUs) of specific languages. Rust, as of writing, is not currently
> > supported by pahole and if it's used with a build that has BTF debugging
> > enabled it results in malformed kernel and module binaries (see
> > Rust-for-Linux/linux#735). So it's better for pahole to exclude Rust
> > CUs until support for it arrives.
> >
> > Reviewed-by: Eric Curtin <ecurtin@redhat.com>
> > Tested-by: Eric Curtin <ecurtin@redhat.com>
> > Reviewed-by: Neal Gompa <neal@gompa.dev>
> > Tested-by: Neal Gompa <neal@gompa.dev>
> > Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
> > ---
> > V1 -> V2: Removed dependency on auto.conf
> >
> >  init/Kconfig              | 2 +-
> >  lib/Kconfig.debug         | 9 +++++++++
> >  scripts/Makefile.modfinal | 4 ++++
> >  scripts/link-vmlinux.sh   | 4 ++++
> >  4 files changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 694f7c160c9c..360aef8d7292 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1913,7 +1913,7 @@ config RUST
> >         depends on !MODVERSIONS
> >         depends on !GCC_PLUGINS
> >         depends on !RANDSTRUCT
> > -       depends on !DEBUG_INFO_BTF
> > +       depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
> >         select CONSTRUCTORS
> >         help
> >           Enables Rust support in the kernel.
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index ea4c903c9868..d473d491e709 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -364,6 +364,15 @@ config PAHOLE_HAS_BTF_TAG
> >           btf_decl_tag) or not. Currently only clang compiler implements
> >           these attributes, so make the config depend on CC_IS_CLANG.
> >
> > +config PAHOLE_HAS_LANG_EXCLUDE
> > +       def_bool PAHOLE_VERSION >= 124
> > +       help
> > +         Support for the --lang_exclude flag which makes pahole exclude
> > +         compilation units from the supplied language. Used in Kbuild to
> > +         omit Rust CUs which are not supported in version 1.24 of pahole,
> > +         otherwise it would emit malformed kernel and module binaries when
> > +         using DEBUG_INFO_BTF_MODULES.
> > +
> >  config DEBUG_INFO_BTF_MODULES
> >         def_bool y
> >         depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
> > diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> > index 25bedd83644b..a880f2d6918f 100644
> > --- a/scripts/Makefile.modfinal
> > +++ b/scripts/Makefile.modfinal
> > @@ -30,6 +30,10 @@ quiet_cmd_cc_o_c = CC [M]  $@
> >
> >  ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
> >
> > +ifdef CONFIG_RUST
> > +PAHOLE_FLAGS += --lang_exclude=rust
> > +endif
> > +
> >  quiet_cmd_ld_ko_o = LD [M]  $@
> >        cmd_ld_ko_o +=                                                   \
> >         $(LD) -r $(KBUILD_LDFLAGS)                                      \
> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> > index 918470d768e9..69eb0bea89bf 100755
> > --- a/scripts/link-vmlinux.sh
> > +++ b/scripts/link-vmlinux.sh
> > @@ -122,6 +122,10 @@ gen_btf()
> >                 return 1
> >         fi
> >
> > +       if is_enabled CONFIG_RUST; then
> > +               PAHOLE_FLAGS="${PAHOLE_FLAGS} --lang_exclude=rust"
> > +       fi
>
> If it was me, I would do things more like v1 of the patch (instead
> just checking pahole version), because this is the only flag set in
> scripts/Makefile.modfinal, which is a little confusing and
> inconsistent. It's ok to set --lang_exclude=rust in all cases, as long
> as pahole_ver is recent enough.
>
> +if [ "${pahole_ver}" -ge "124" ]; then
> +       # see PAHOLE_HAS_LANG_EXCLUDE
> +       extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> +fi
>
> But I'm not too opinionated either on this so...
>
> Reviewed-by: Eric Curtin <ecurtin@redhat.com>
>
> can be reapplied. I'm gonna test this again to see if it works in a
> Fedora Asahi rpm build.

After testing I probably have to retract my Reviewed-by tag,
apologies, bpf and all that did not work with this patch when I built
in the fedora way, but, the good news is when I alter v1 of the patch
to just check pahole version like so (instead of the is_enabled
check):

+if [ "${pahole_ver}" -ge "124" ]; then
+        # see PAHOLE_HAS_LANG_EXCLUDE
+        extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
+fi

it worked just fine, and that should satisfy the testbot and all the
other ways we build too. Could we change to that @Martin Rodriguez
Reboredo ?

>
>
> > +
> >         vmlinux_link ${1}
> >
> >         info "BTF" ${2}
> > --
> > 2.39.0
> >