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Date: Tue, 17 Oct 2023 19:37:40 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: linux-kbuild@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
Masahiro Yamada <masahiroy@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Alice Ryhl <aliceryhl@...gle.com>,
Andreas Hindborg <a.hindborg@...sung.com>,
Andrii Nakryiko <andrii@...nel.org>,
Benno Lossin <benno.lossin@...ton.me>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Boqun Feng <boqun.feng@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Gary Guo <gary@...yguo.net>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Miguel Ojeda <ojeda@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nicolas Schier <nicolas@...sle.eu>, Song Liu <song@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Yonghong Song <yonghong.song@...ux.dev>, bpf@...r.kernel.org,
rust-for-linux@...r.kernel.org
Subject: [PATCH 2/4] kbuild: avoid too many execution of scripts/pahole-flags.sh
scripts/pahole-flags.sh is executed so many times.
You can check how many times it is invoked during the build, as follows:
$ cat <<EOF >> scripts/pahole-flags.sh
> echo "scripts/pahole-flags.sh was executed" >&2
> EOF
$ make -s
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
[ lots of repeated lines suppressed... ]
This scripts is exectuted more than 20 times during the kernel build
because PAHOLE_FLAGS is a recursively expanded variable and exported
to sub-processes.
With the GNU Make >= 4.4, it is executed more than 60 times because
exported variables are also passed to other $(shell ) invocations.
Without careful coding, it is known to cause an exponential fork
explosion. [1]
The use of $(shell ) in an exported recursive variable is likely wrong
because $(shell ) is always evaluated due to the 'export' keyword, and
the evaluation can occur multiple times by the nature of recursive
variables.
Convert the shell script to a Makefile, which is included only when
CONFIG_DEBUG_INFO_BTF=y.
[1]: https://savannah.gnu.org/bugs/index.php?64746
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---
Makefile | 4 +---
scripts/Makefile.btf | 19 +++++++++++++++++++
scripts/pahole-flags.sh | 30 ------------------------------
3 files changed, 20 insertions(+), 33 deletions(-)
create mode 100644 scripts/Makefile.btf
delete mode 100755 scripts/pahole-flags.sh
diff --git a/Makefile b/Makefile
index fed9a6cc3665..eaddec67e5e1 100644
--- a/Makefile
+++ b/Makefile
@@ -513,8 +513,6 @@ LZ4 = lz4c
XZ = xz
ZSTD = zstd
-PAHOLE_FLAGS = $(shell PAHOLE=$(PAHOLE) $(srctree)/scripts/pahole-flags.sh)
-
CHECKFLAGS := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
-Wbitwise -Wno-return-void -Wno-unknown-attribute $(CF)
NOSTDINC_FLAGS :=
@@ -605,7 +603,6 @@ export KBUILD_RUSTFLAGS RUSTFLAGS_KERNEL RUSTFLAGS_MODULE
export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_RUSTFLAGS_MODULE KBUILD_LDFLAGS_MODULE
export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL KBUILD_RUSTFLAGS_KERNEL
-export PAHOLE_FLAGS
# Files to ignore in find ... statements
@@ -1002,6 +999,7 @@ KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
# include additional Makefiles when needed
include-y := scripts/Makefile.extrawarn
include-$(CONFIG_DEBUG_INFO) += scripts/Makefile.debug
+include-$(CONFIG_DEBUG_INFO_BTF)+= scripts/Makefile.btf
include-$(CONFIG_KASAN) += scripts/Makefile.kasan
include-$(CONFIG_KCSAN) += scripts/Makefile.kcsan
include-$(CONFIG_KMSAN) += scripts/Makefile.kmsan
diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
new file mode 100644
index 000000000000..82377e470aed
--- /dev/null
+++ b/scripts/Makefile.btf
@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0
+
+pahole-ver := $(CONFIG_PAHOLE_VERSION)
+pahole-flags-y :=
+
+# pahole 1.18 through 1.21 can't handle zero-sized per-CPU vars
+ifeq ($(call test-le, $(pahole-ver), 121),y)
+pahole-flags-$(call test-ge, $(pahole-ver), 118) += --skip_encoding_btf_vars
+endif
+
+pahole-flags-$(call test-ge, $(pahole-ver), 121) += --btf_gen_floats
+
+pahole-flags-$(call test-ge, $(pahole-ver), 122) += -j
+
+pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE) += --lang_exclude=rust
+
+pahole-flags-$(call test-ge, $(pahole-ver), 125) += --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
+
+export PAHOLE_FLAGS := $(pahole-flags-y)
diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
deleted file mode 100755
index 728d55190d97..000000000000
--- a/scripts/pahole-flags.sh
+++ /dev/null
@@ -1,30 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0
-
-extra_paholeopt=
-
-if ! [ -x "$(command -v ${PAHOLE})" ]; then
- exit 0
-fi
-
-pahole_ver=$($(dirname $0)/pahole-version.sh ${PAHOLE})
-
-if [ "${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"
-fi
-if [ "${pahole_ver}" -ge "121" ]; then
- extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
-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
-if [ "${pahole_ver}" -ge "125" ]; then
- extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
-fi
-
-echo ${extra_paholeopt}
--
2.40.1
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