diff mbox series

[bpf-next,v2,2/4] kbuild: avoid too many execution of scripts/pahole-flags.sh

Message ID 20231018151950.205265-2-masahiroy@kernel.org (mailing list archive)
State New, archived
Headers show
Series [bpf-next,v2,1/4] kbuild: remove ARCH_POSTLINK from module builds | expand

Commit Message

Masahiro Yamada Oct. 18, 2023, 3:19 p.m. UTC 
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 executed 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@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>
---

Changes in v2:
 - Fix a typo in commit description
 - Update MAINTAINERS

 MAINTAINERS             |  2 +-
 Makefile                |  4 +---
 scripts/Makefile.btf    | 19 +++++++++++++++++++
 scripts/pahole-flags.sh | 30 ------------------------------
 4 files changed, 21 insertions(+), 34 deletions(-)
 create mode 100644 scripts/Makefile.btf
 delete mode 100755 scripts/pahole-flags.sh

Comments

Jiri Olsa Oct. 19, 2023, 8:47 a.m. UTC | #1 
On Thu, Oct 19, 2023 at 12:19:48AM +0900, Masahiro Yamada wrote:
> 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 executed 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@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>

nice!

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka


> ---
> 
> Changes in v2:
>  - Fix a typo in commit description
>  - Update MAINTAINERS
> 
>  MAINTAINERS             |  2 +-
>  Makefile                |  4 +---
>  scripts/Makefile.btf    | 19 +++++++++++++++++++
>  scripts/pahole-flags.sh | 30 ------------------------------
>  4 files changed, 21 insertions(+), 34 deletions(-)
>  create mode 100644 scripts/Makefile.btf
>  delete mode 100755 scripts/pahole-flags.sh
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 35977b269d5e..a08d558b1aaa 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -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/
> 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
>
Martin Rodriguez Reboredo Oct. 23, 2023, 12:33 a.m. UTC | #2 
On 10/18/23 12:19, Masahiro Yamada wrote:
> 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 executed 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@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>
> ---
> [...]
> @@ -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

Would've used a tab, for legibility sake.

>   include-$(CONFIG_KASAN)		+= scripts/Makefile.kasan
>   include-$(CONFIG_KCSAN)		+= scripts/Makefile.kcsan
>   include-$(CONFIG_KMSAN)		+= scripts/Makefile.kmsan
> [...]
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
diff mbox series

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index 35977b269d5e..a08d558b1aaa 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -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/
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}