linux-kernel - Re: [PATCH v2] kbuild: pahole-version: improve overall checking and error messages

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Message-ID: <20240903-super-elk-of-bliss-eaed2c@lindesnes>
Date: Tue, 3 Sep 2024 21:48:59 +0200
From: Nicolas Schier <nicolas@...sle.eu>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH v2] kbuild: pahole-version: improve overall checking and
 error messages

On Mon, Sep 02, 2024 at 06:08:28PM +0200, Miguel Ojeda wrote:
> Like patch "rust: suppress error messages from
> CONFIG_{RUSTC,BINDGEN}_VERSION_TEXT" [1], do not assume the file existing
> and being executable implies executing it will succeed.
> 
> Instead, bail out if executing it fails for any reason, as well as if
> the program does not print to standard output what we are expecting from
> `pahole --version`. The script needs to ensure that it always returns
> an integer, since its output will go into a Kconfig `int`-type symbol.
> 
> In addition, check whether the program exists first, and provide
> error messages for each error condition, similar to how it is done in
> e.g. `scripts/rust_is_available.sh`.
> 
> For instance, currently `pahole` may be built for another architecture
> or may be a program we do not expect that fails:
> 
>     $ echo 'bad' > bad-pahole
>     $ chmod u+x bad-pahole
>     $ make PAHOLE=./bad-pahole defconfig
>     ...
>     ./bad-pahole: 1: bad: not found
>     init/Kconfig:112: syntax error
>     init/Kconfig:112: invalid statement
> 
> With this applied, we get instead:
> 
>     ***
>     *** Running './bad-pahole' to check the pahole version failed with
>     *** code 127. pahole will not be used.
>     ***
>     ...
>     $ grep CONFIG_PAHOLE_VERSION .config
>     CONFIG_PAHOLE_VERSION=0
> 
> Similarly, `pahole` currently may be a program that returns successfully,
> but that does not print the version that we would expect:
> 
>     $ echo 'echo' > bad-pahole
>     $ chmod u+x bad-pahole
>     $ make PAHOLE=./bad-pahole defconfig
>     ...
>     init/Kconfig:114: syntax error
>     init/Kconfig:114: invalid statement
> 
> With this applied, we get instead:
> 
>     ***
>     *** pahole './bad-pahole' returned an unexpected version output.
>     *** pahole will not be used.
>     ***
>     ...
>     $ grep CONFIG_PAHOLE_VERSION .config
>     CONFIG_PAHOLE_VERSION=0
> 
> Finally, with this applied, if the program does not exist, we get:
> 
>     $ make PAHOLE=./bad-pahole defconfig
>     ...
>     ***
>     *** pahole './bad-pahole' could not be found. pahole will not be used.
>     ***
>     ...
>     $ grep CONFIG_PAHOLE_VERSION .config
>     CONFIG_PAHOLE_VERSION=0
> 
> Link: https://lore.kernel.org/rust-for-linux/20240727140302.1806011-1-masahiroy@kernel.org/ [1]
> Co-developed-by: Nicolas Schier <nicolas@...sle.eu>
> Signed-off-by: Nicolas Schier <nicolas@...sle.eu>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
> v1: https://lore.kernel.org/all/20240728125527.690726-1-ojeda@kernel.org/
> v2:
> 
> Reworked to catch successful programs that may not output what we expect from
> pahole as well as to do the checking step-by-step (for better error messages).
> 
> I didn't change the regular expression to reduce the changes (except adding
> `p`) -- it can be improved separately.
> 
> Also, please note that I added Nicolas as co-author since he proposed part of
> the solution, but he has not formally signed off yet.

thanks, no objections.

>  scripts/pahole-version.sh | 30 +++++++++++++++++++++++++++---
>  1 file changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/scripts/pahole-version.sh b/scripts/pahole-version.sh
> index f8a32ab93ad1..cdb80a3d6e4f 100755
> --- a/scripts/pahole-version.sh
> +++ b/scripts/pahole-version.sh
> @@ -5,9 +5,33 @@
>  #
>  # Prints pahole's version in a 3-digit form, such as 119 for v1.19.
> 
> -if [ ! -x "$(command -v "$@")" ]; then
> -	echo 0
> +set -e
> +trap "echo 0; exit 1" EXIT
> +
> +if ! command -v "$@" >/dev/null; then
> +	echo >&2 "***"
> +	echo >&2 "*** pahole '$@' could not be found. pahole will not be used."

shellcheck likes to have '$*' instead of '$@', but I can't think of a
set of arguments which might cause problems.

> +	echo >&2 "***"
> +	exit 1
> +fi
> +
> +output=$("$@" --version 2>/dev/null) || code=$?
> +if [ -n "$code" ]; then
> +	echo >&2 "***"
> +	echo >&2 "*** Running '$@' to check the pahole version failed with"
> +	echo >&2 "*** code $code. pahole will not be used."
> +	echo >&2 "***"
> +	exit 1
> +fi
> +
> +output=$(echo "$output" | sed -nE 's/v([0-9]+)\.([0-9]+)/\1\2/p')

I'd rather like to have

    output=$(echo "$output" | sed -nE 's/v([0-9]+)\.([0-9][0-9])/\1\2/p')

here (thus, explicitly check against a two number subversion), so that
we can detect also versions like 1.100 or 2.1 and bail out.

Kind regards,
Nicolas