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

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

[Thomas Weißschuh]

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@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202610131613.BpOi6VPp-lkp@intel.com/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 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@linutronix.de>

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@intel.com>
> Link: https://lore.kernel.org/oe-kbuild-all/202610131613.BpOi6VPp-lkp@intel.com/
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

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@linutronix.de>
> 

-- 
Cheers,
Nathan

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

[Thomas Weißschuh]

On Wed, Oct 14, 2026 at 02:40:43PM -0700, Nathan Chancellor wrote:
> 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@intel.com>
> > Link: https://lore.kernel.org/oe-kbuild-all/202610131613.BpOi6VPp-lkp@intel.com/
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> 
> 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).

It actually breaks modversions quite badly. And it is not obvious to debug
as that uses the pipe in an `if` statement which swallows the 141 silently.

Not sure what to do here.

Maybe we just provide `try-pipefail` so users can opt-in where it makes sense.


Also

try-pipefail = set -o pipefail || true 2>/dev/null

should have been

try-pipefail = set -o pipefail 2>/dev/null || true

> > ---
> >  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

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

[Nathan Chancellor]

On Thu, Oct 15, 2026 at 12:15:18PM +0200, Thomas Weißschuh wrote:
> It actually breaks modversions quite badly. And it is not obvious to debug

Welp, good to know I wasn't very far off with that review comment :)

> as that uses the pipe in an `if` statement which swallows the 141 silently.

Ah yeah, great point.

> Not sure what to do here.
> 
> Maybe we just provide `try-pipefail` so users can opt-in where it makes sense.

Yeah, that seems like a much more reasonable starting point, as
something like this should likely be considered on a case-by-case basis
anyways.

-- 
Cheers,
Nathan