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kbuild: avoid too many execution of scripts/pahole-flags.sh

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scripts/pahole-flags.sh is executed so many times.

You can confirm it, 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... ]

This scripts is executed more than 20 times during the kernel build
because PAHOLE_FLAGS is a recursively expanded variable and exported
to sub-processes.

With 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@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
Tested-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
This commit is contained in:
Masahiro Yamada 2023-10-19 00:19:48 +09:00
parent 7f6d8f7e43
commit 72d091846d
4 changed files with 21 additions and 34 deletions
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2
MAINTAINERS
View File

@ -3742,7 +3742,7 @@ F: net/sched/act_bpf.c
F: net/sched/cls_bpf.c
F: samples/bpf/
F: scripts/bpf_doc.py
F: scripts/pahole-flags.sh
F: scripts/Makefile.btf
F: scripts/pahole-version.sh
F: tools/bpf/
F: tools/lib/bpf/

4
Makefile
View File

@ -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

19
scripts/Makefile.btf Normal file
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@ -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)

30
scripts/pahole-flags.sh
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@ -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}