From: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
To: Masahiro Yamada <masahiroy@kernel.org>, linux-kbuild@vger.kernel.org
Cc: linux-kernel@vger.kernel.org,
"Alan Maguire" <alan.maguire@oracle.com>,
"Nicolas Schier" <n.schier@avm.de>,
"Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Alice Ryhl" <aliceryhl@google.com>,
"Andreas Hindborg" <a.hindborg@samsung.com>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Benno Lossin" <benno.lossin@proton.me>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Boqun Feng" <boqun.feng@gmail.com>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Gary Guo" <gary@garyguo.net>, "Hao Luo" <haoluo@google.com>,
"Jiri Olsa" <jolsa@kernel.org>,
"John Fastabend" <john.fastabend@gmail.com>,
"KP Singh" <kpsingh@kernel.org>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Nathan Chancellor" <nathan@kernel.org>,
"Nick Desaulniers" <ndesaulniers@google.com>,
"Nicolas Schier" <nicolas@fjasle.eu>,
"Song Liu" <song@kernel.org>,
"Stanislav Fomichev" <sdf@google.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Yonghong Song" <yonghong.song@linux.dev>,
bpf@vger.kernel.org, rust-for-linux@vger.kernel.org
Subject: Re: [bpf-next PATCH v2 2/4] kbuild: avoid too many execution of scripts/pahole-flags.sh
Date: Sun, 22 Oct 2023 21:33:58 -0300 [thread overview]
Message-ID: <4c926cff-a3f2-445e-9ca2-9effad423cb7@gmail.com> (raw)
In-Reply-To: <20231018151950.205265-2-masahiroy@kernel.org>
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>
next prev parent reply other threads:[~2023-10-23 0:34 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-18 15:19 [bpf-next PATCH v2 1/4] kbuild: remove ARCH_POSTLINK from module builds Masahiro Yamada
2023-10-18 15:19 ` Masahiro Yamada
2023-10-18 15:19 ` Masahiro Yamada
2023-10-18 15:19 ` [bpf-next PATCH v2 2/4] kbuild: avoid too many execution of scripts/pahole-flags.sh Masahiro Yamada
2023-10-19 8:47 ` Jiri Olsa
2023-10-23 0:33 ` Martin Rodriguez Reboredo [this message]
2023-10-18 15:19 ` [bpf-next PATCH v2 3/4] kbuild: skip module BTF with one-time check for vmlinux Masahiro Yamada
2023-10-19 8:17 ` Jiri Olsa
2023-10-18 15:19 ` [bpf-next PATCH v2 4/4] kbuild: refactor module BTF rule Masahiro Yamada
2023-10-18 15:49 ` Nicolas Schier
2023-10-19 8:15 ` Jiri Olsa
2023-10-19 22:54 ` Andrii Nakryiko
2023-10-20 7:03 ` Masahiro Yamada
2023-10-20 20:51 ` Andrii Nakryiko
2023-10-21 11:37 ` Masahiro Yamada
2023-10-21 19:33 ` Andrii Nakryiko
2023-10-22 20:23 ` Masahiro Yamada
2023-10-23 3:19 ` Andrii Nakryiko
2023-10-28 12:00 ` Masahiro Yamada
2023-10-28 13:36 ` Jiri Olsa
2023-10-31 18:44 ` Andrii Nakryiko
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