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

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Date:   Tue, 20 Dec 2022 17:39:15 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     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>,
        Eric Curtin <ecurtin@...hat.com>, Neal Gompa <neal@...pa.dev>
Subject: [PATCH bpf] scripts: Exclude Rust CUs with pahole

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@...hat.com>
Tested-by: Eric Curtin <ecurtin@...hat.com>
Reviewed-by: Neal Gompa <neal@...pa.dev>
Tested-by: Neal Gompa <neal@...pa.dev>
Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>
---
 init/Kconfig            | 2 +-
 lib/Kconfig.debug       | 9 +++++++++
 scripts/pahole-flags.sh | 8 ++++++++
 3 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/pahole-flags.sh b/scripts/pahole-flags.sh
index 0d99ef17e4a5..1071d2cd9b28 100755
--- a/scripts/pahole-flags.sh
+++ b/scripts/pahole-flags.sh
@@ -9,6 +9,10 @@ fi
 
 pahole_ver=$($(dirname $0)/pahole-version.sh ${PAHOLE})
 
+is_enabled() {
+	grep -q "^$1=y" include/config/auto.conf
+}
+
 if [ "${pahole_ver}" -ge "118" ] && [ "${pahole_ver}" -le "121" ]; then
 	# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
 	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_vars"
@@ -19,5 +23,9 @@ fi
 if [ "${pahole_ver}" -ge "122" ]; then
 	extra_paholeopt="${extra_paholeopt} -j"
 fi
+if is_enabled CONFIG_RUST; then
+	# see PAHOLE_HAS_LANG_EXCLUDE
+	extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
+fi
 
 echo ${extra_paholeopt}
-- 
2.39.0