linux-kernel - [PATCH v3] scripts: Exclude Rust CUs with pahole

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Date:   Wed, 11 Jan 2023 12:20:50 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Neal Gompa <neal@...pa.dev>, Eric Curtin <ecurtin@...hat.com>,
        bpf@...r.kernel.org, rust-for-linux@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Yonghong Song <yhs@...com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Subject: [PATCH v3] scripts: Exclude Rust CUs with pahole

Version 1.24 of pahole has the capability to exclude compilation units
(CUs) of specific languages [1] [2]. 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 [3]. So it's better for pahole to exclude Rust CUs until
support for it arrives.

Link: https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=49358dfe2aaae4e90b072332c3e324019826783f [1]
Link: https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=8ee363790b7437283c53090a85a9fec2f0b0fbc4 [2]
Link: https://github.com/Rust-for-Linux/linux/issues/735 [3]

Co-developed-by: Eric Curtin <ecurtin@...hat.com>
Signed-off-by: Eric Curtin <ecurtin@...hat.com>
Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>
---
V2 -> V3: Enable pahole option upon comparing with version 1.24
V1 -> V2: Removed dependency on auto.conf

 init/Kconfig            | 2 +-
 lib/Kconfig.debug       | 9 +++++++++
 scripts/pahole-flags.sh | 4 ++++
 3 files changed, 14 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/pahole-flags.sh b/scripts/pahole-flags.sh
index 0d99ef17e4a5..1f1f1d397c39 100755
--- a/scripts/pahole-flags.sh
+++ b/scripts/pahole-flags.sh
@@ -19,5 +19,9 @@ fi
 if [ "${pahole_ver}" -ge "122" ]; then
 	extra_paholeopt="${extra_paholeopt} -j"
 fi
+if [ "${pahole_ver}" -ge "124" ]; then
+	# see PAHOLE_HAS_LANG_EXCLUDE
+	extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
+fi
 
 echo ${extra_paholeopt}
-- 
2.39.0