[PATCH v2] scripts: Exclude Rust CUs with pahole

[Martin Rodriguez Reboredo <yakoyoku@gmail.com>]

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