On Sun, 8 Jan 2023 at 02:15, Martin Rodriguez Reboredo
<yakoyoku@xxxxxxxxx> 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@xxxxxxxxxx>
> Tested-by: Eric Curtin <ecurtin@xxxxxxxxxx>
> Reviewed-by: Neal Gompa <neal@xxxxxxxxx>
> Tested-by: Neal Gompa <neal@xxxxxxxxx>
> Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@xxxxxxxxx>
> ---
> 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@xxxxxxxxxx>
can be reapplied. I'm gonna test this again to see if it works in a
Fedora Asahi rpm build.
> +
> vmlinux_link ${1}
>
> info "BTF" ${2}
> --
> 2.39.0
>
