Commit 72d09184 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

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

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: default avatarMasahiro Yamada <masahiroy@kernel.org>
Reviewed-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Tested-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Reviewed-by: default avatarNicolas Schier <n.schier@avm.de>
Tested-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Acked-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Reviewed-by: default avatarMartin Rodriguez Reboredo <yakoyoku@gmail.com>
parent 7f6d8f7e

MAINTAINERS

+1 −1
Original line number Diff line number Diff line
@@ -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/

Makefile

+1 −3
Original line number Diff line number Diff line
@@ -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

scripts/Makefile.btf

0 → 100644
+19 −0
Original line number Diff line number Diff line 
# 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)

scripts/pahole-flags.sh

deleted100755 → 0
+0 −30
Original line number Diff line number Diff line 
#!/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}