Re: [PATCH v4] scripts/config: honor $KBUILD_OUTPUT by default

[Nathan Chancellor]

Hi Dmitry,

> If $KBUILD_OUTPUT is set, use it by default if --file is not passed.
> 
> Fix the issue when the script silently updates a stale .config in
> the root directory, while the user expects ${KBUILD_OUTPUT}/.config
> to be updated.
> Handle properly if the config file is a relative path.
> 
> The problem can be worked around with --file, but this is easy to miss,
> and is inconsistent with how the Makefile and other tools work
> (e.g., scripts/diffconfig).
> 
> How to reproduce the issue:
> 	rm .config
> 	export KBUILD_OUTPUT=.out
> 	make defconfig
> 	./scripts/config \
> 	       -e CONFIG_UBSAN
> 	grep: .config: No such file or directory
> 
> How the patch was tested:
> 	make mrproper
> 	export KBUILD_OUTPUT=.out
> 	make defconfig
> 	grep "CONFIG_UBSAN=y" $KBUILD_OUTPUT/.config || echo "OK"
> 
> Test the basic usage:
> 	./scripts/config -e CONFIG_UBSAN
> 	grep "CONFIG_UBSAN=y" $KBUILD_OUTPUT/.config && echo "OK"
> 
> Test --refresh picks up correct config file by using $KBUILD_OUTPUT
> 	./scripts/config -d CONFIG_UBSAN
> 	./scripts/config --refresh -e CONFIG_UBSAN
> 	grep "CONFIG_UBSAN=y" $KBUILD_OUTPUT/.config && echo "OK"
> 
> Test --file takes precedence over $KBUILD_OUTPUT and
> a relative path is handled properly
> 	./scripts/config -d CONFIG_UBSAN
> 	mkdir .out2
> 	cp .out/.config .out2/.my_config
> 	grep "CONFIG_UBSAN=y" .out2/.my_config
> 	./scripts/config --file .out2/.my_config --refresh \
> 	       -e CONFIG_UBSAN
> 	grep "CONFIG_UBSAN=y" .out2/.my_config && echo "OK"
> 	ls .out/.out2 || echo "OK"
> 	ls .out/.out || echo "OK"
> 
> Signed-off-by: Dmitry Voytik <voytikd@xxxxxxxxx>
> ---
> v4:
>  - Addressed Nicolas Schier's comments - dropped the change how '--refresh'
>    is handled
>  - Implemented conversion of $FN to the absolute path which helps with
>    '--refresh' and relative paths
>  - Documented testing steps in the commit message
> v3:
>  - Added an example in the commit message how to reproduce the issue
> v2:
>  - Addressed comments by sashiko:
>    - https://sashiko.dev/#/patchset/20260920064350.17999-1-voytikd%40gmail.com
>    - use basename when --refresh is used
>    - remove echo which can be misleading when --file is passed
> v1:
>  - https://lore.kernel.org/all/20260920064350.17999-1-voytikd@xxxxxxxxx/
> ---
>  scripts/config | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/scripts/config b/scripts/config
> index 32428ea909c2..0b28fc498195 100755
> --- a/scripts/config
> +++ b/scripts/config
> @@ -130,6 +130,10 @@ on_exit() {
>  trap on_exit EXIT
>  
>  FN=.config
> +if [ -n "${KBUILD_OUTPUT}" ]; then
> +	FN=${KBUILD_OUTPUT}/${FN}
> +fi
> +
>  CMDS=()
>  while [[ $# -gt 0 ]]; do
>  	if [ "$1" = "--file" ]; then
> @@ -143,6 +147,7 @@ while [[ $# -gt 0 ]]; do
>  		shift
>  	fi
>  done
> +FN=$(realpath "$FN")

Sashiko has a couple of comments here:

  https://sashiko.dev/#/patchset/20261001214618.283635-1-voytikd%40gmail.com

The second comment around KBUILD_OUTPUT / '--file' beginning with '-' is
a fairly contrived example but sticking '--' in there does not seem like
an unreasonable hardening move.

As for the first comment, I am not sure I want to rely on 'realpath -m'
since that is a coreutils-ism and up until now, this could work on any
operating system (as least as far as I can tell). Maybe we could do
something like

  FN=$(realpath -q -- "$FN" || echo "$FN")

to just try and hobble along if we cannot resolve $FN properly but maybe
there is a better solution that I am just not seeing at the moment.

-- 
Cheers,
Nathan