Re: [PATCH RFC] kbuild: enable pipefail for commands where possible

[Nathan Chancellor]

On Wed, Oct 14, 2026 at 10:30:30AM +0200, Thomas Weißschuh wrote:
> The exit status of a shell pipeline by default only depends on the exit
> status of its last command. If an earlier command fails this is silently
> ignored. In this case the build continues operating on intermediate
> state, potentially leading to confusing follow-up failures.
> 
> The 'pipefail' option can be used to exit the pipeline with an error as
> soon as a single of its command fails which 'set -e' will elevate to
> error exit of the whole command.
> 
> 'pipefail' has been only standardized in POSIX 2024, but it is supported
> by many shells anyways, including bash and dash. To avoid issues with
> shells not implementing it, ignore failures silently.
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Link: https://lore.kernel.org/oe-kbuild-all/202610131613.BpOi6VPp-lkp@xxxxxxxxx/
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>

This is probably the right thing to do but it makes me nervous. pipefail
is very easy to hold wrong mainly because of SIGPIPE:

  $ cat test.sh
  set -o pipefail

  yes | head -n +50

  $ bash test.sh
  ...

  $ echo $?
  141

and debugging that is unlikely to be obvious (but maybe it will because
the error would be 141).

> ---
>  scripts/Kbuild.include | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 8c311b997e24..1975d2739cdb 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -149,8 +149,11 @@ delete-on-interrupt = \
>  		$(foreach sig, HUP INT QUIT TERM PIPE, \
>  			trap 'rm -f $@; trap - $(sig); kill -s $(sig) $$$$' $(sig);))
>  
> +# try to enable pipefail
> +try-pipefail = set -o pipefail || true 2>/dev/null
> +
>  # print and execute commands
> -cmd = @$(if $(cmd_$(1)),set -e; $($(quiet)log_print) $(delete-on-interrupt) $(cmd_$(1)),:)
> +cmd = @$(if $(cmd_$(1)),$(try-pipefail); set -e; $($(quiet)log_print) $(delete-on-interrupt) $(cmd_$(1)),:)
>  
>  ###
>  # if_changed      - execute command if any prerequisite is newer than
> 
> ---
> base-commit: 27286bf096c51df05eec6664f18b945f8dd61c0e
> change-id: 20261013-kbuild-error-propagation-8ab5f649ff36
> 
> Best regards,
> --  
> Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> 

-- 
Cheers,
Nathan