[PATCH 0/2] kbuild: Follow-up to "Reject unexpected values for LLVM="

[PATCH 0/2] kbuild: Follow-up to "Reject unexpected values for LLVM="

[Thomas Weißschuh]

Some cleanups.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Thomas Weißschuh (2):
      Documentation/llvm: drop note about LLVM=0
      tools/build: Reject unexpected values for LLVM=

 Documentation/kbuild/llvm.rst  | 4 ----
 tools/scripts/Makefile.include | 2 ++
 2 files changed, 2 insertions(+), 4 deletions(-)
---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260226-kbuild-llvm-followup-5ad6253f85c8

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

[PATCH 1/2] Documentation/llvm: drop note about LLVM=0

[Thomas Weißschuh]

Since commit 502678b88cb3 ("kbuild: Reject unexpected values for LLVM=")
LLVM=0 generates an error instead of silently behaving unexpectedly.

Drop the now unnecessary note.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 Documentation/kbuild/llvm.rst | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index bc8a283bc44b..441d8786fcbc 100644
--- a/Documentation/kbuild/llvm.rst
+++ b/Documentation/kbuild/llvm.rst
@@ -71,10 +71,6 @@ recommend::
 
 	PATH=/path/to/llvm/:$PATH make LLVM=-14
 
-``LLVM=0`` is not the same as omitting ``LLVM`` altogether, it will behave like
-``LLVM=1``. If you only wish to use certain LLVM utilities, use their
-respective make variables.
-
 The same value used for ``LLVM=`` should be set for each invocation of ``make``
 if configuring and building via distinct commands. ``LLVM=`` should also be set
 as an environment variable when running scripts that will eventually run

-- 
2.53.0

[PATCH 2/2] tools/build: Reject unexpected values for LLVM=

[Thomas Weißschuh]

Since commit 502678b88cb3 ("kbuild: Reject unexpected values for LLVM=")
the regular kbuild rejects unexpected values of LLVM=1 instead of
silently treating them as LLVM=1.

Align the tools build to kbuild.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

---
There is no formal maintainer for this file.
IMO this change should go through kbuild.
---
 tools/scripts/Makefile.include | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index b5ecf137febc..41971a68972d 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -56,6 +56,8 @@ ifneq ($(filter %/,$(LLVM)),)
 LLVM_PREFIX := $(LLVM)
 else ifneq ($(filter -%,$(LLVM)),)
 LLVM_SUFFIX := $(LLVM)
+else ifneq ($(LLVM),1)
+$(error Invalid value for LLVM, see Documentation/kbuild/llvm.rst)
 endif
 
 $(call allow-override,CC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))

-- 
2.53.0

Re: [PATCH 1/2] Documentation/llvm: drop note about LLVM=0

[Nathan Chancellor]

On Thu, Feb 26, 2026 at 10:23:57PM +0100, Thomas Weißschuh wrote:
> Since commit 502678b88cb3 ("kbuild: Reject unexpected values for LLVM=")
> LLVM=0 generates an error instead of silently behaving unexpectedly.
> 
> Drop the now unnecessary note.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

It might be worth keeping the note about LLVM=0 not being the same as
omitting LLVM altogether, as neither the documentation nor the error
message will say why that is not a valid value. Maybe:

  ``LLVM=0`` is not the same as omitting ``LLVM`` altogether. If you
  only wish to use certain LLVM utilities, use their respective make
  variables.

I don't feel that strongly about it though. Regardless:

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  Documentation/kbuild/llvm.rst | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> index bc8a283bc44b..441d8786fcbc 100644
> --- a/Documentation/kbuild/llvm.rst
> +++ b/Documentation/kbuild/llvm.rst
> @@ -71,10 +71,6 @@ recommend::
>  
>  	PATH=/path/to/llvm/:$PATH make LLVM=-14
>  
> -``LLVM=0`` is not the same as omitting ``LLVM`` altogether, it will behave like
> -``LLVM=1``. If you only wish to use certain LLVM utilities, use their
> -respective make variables.
> -
>  The same value used for ``LLVM=`` should be set for each invocation of ``make``
>  if configuring and building via distinct commands. ``LLVM=`` should also be set
>  as an environment variable when running scripts that will eventually run
> 
> -- 
> 2.53.0
> 

Re: [PATCH 2/2] tools/build: Reject unexpected values for LLVM=

[Nathan Chancellor]

On Thu, Feb 26, 2026 at 10:23:58PM +0100, Thomas Weißschuh wrote:
> Since commit 502678b88cb3 ("kbuild: Reject unexpected values for LLVM=")
> the regular kbuild rejects unexpected values of LLVM=1 instead of
> silently treating them as LLVM=1.
> 
> Align the tools build to kbuild.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> 
> ---
> There is no formal maintainer for this file.
> IMO this change should go through kbuild.

Ironically I just rejected a tools/ patch going through Kbuild:

  https://lore.kernel.org/20260225192505.GC2755225@ax162/

but since there is no formal maintainer, it is the same change done in
Kbuild, and the risk of fallout is much less than that change, I think
we can make an exception and take it.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  tools/scripts/Makefile.include | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> index b5ecf137febc..41971a68972d 100644
> --- a/tools/scripts/Makefile.include
> +++ b/tools/scripts/Makefile.include
> @@ -56,6 +56,8 @@ ifneq ($(filter %/,$(LLVM)),)
>  LLVM_PREFIX := $(LLVM)
>  else ifneq ($(filter -%,$(LLVM)),)
>  LLVM_SUFFIX := $(LLVM)
> +else ifneq ($(LLVM),1)
> +$(error Invalid value for LLVM, see Documentation/kbuild/llvm.rst)
>  endif
>  
>  $(call allow-override,CC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
> 
> -- 
> 2.53.0
> 

Re: [PATCH 2/2] tools/build: Reject unexpected values for LLVM=

[Nicolas Schier]

On Thu, Feb 26, 2026 at 02:45:58PM -0700, Nathan Chancellor wrote:
> On Thu, Feb 26, 2026 at 10:23:58PM +0100, Thomas Weißschuh wrote:
> > Since commit 502678b88cb3 ("kbuild: Reject unexpected values for LLVM=")
> > the regular kbuild rejects unexpected values of LLVM=1 instead of
> > silently treating them as LLVM=1.
> > 
> > Align the tools build to kbuild.
> > 
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > 
> > ---
> > There is no formal maintainer for this file.
> > IMO this change should go through kbuild.
> 
> Ironically I just rejected a tools/ patch going through Kbuild:
> 
>   https://lore.kernel.org/20260225192505.GC2755225@ax162/
> 
> but since there is no formal maintainer, it is the same change done in
> Kbuild, and the risk of fallout is much less than that change, I think
> we can make an exception and take it.

+1

> Reviewed-by: Nathan Chancellor <nathan@kernel.org>

Reviewed-by: Nicolas Schier <nsc@kernel.org>

-- 
Nicolas

Re: [PATCH 1/2] Documentation/llvm: drop note about LLVM=0

[Nicolas Schier]

On Thu, Feb 26, 2026 at 02:43:49PM -0700, Nathan Chancellor wrote:
> On Thu, Feb 26, 2026 at 10:23:57PM +0100, Thomas Weißschuh wrote:
> > Since commit 502678b88cb3 ("kbuild: Reject unexpected values for LLVM=")
> > LLVM=0 generates an error instead of silently behaving unexpectedly.
> > 
> > Drop the now unnecessary note.
> > 
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> 
> It might be worth keeping the note about LLVM=0 not being the same as
> omitting LLVM altogether, as neither the documentation nor the error
> message will say why that is not a valid value. Maybe:
> 
>   ``LLVM=0`` is not the same as omitting ``LLVM`` altogether. If you
>   only wish to use certain LLVM utilities, use their respective make
>   variables.

Yeah, I think that would be a good thing to add, too.

W/ or w/o:

Reviewed-by: Nicolas Schier <nsc@kernel.org>

If nobody complains, I am going to add both patches to kbuild-next
within a few days.

Kind regards,
Nicolas



> I don't feel that strongly about it though. Regardless:
> 
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> 
> > ---
> >  Documentation/kbuild/llvm.rst | 4 ----
> >  1 file changed, 4 deletions(-)
> > 
> > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> > index bc8a283bc44b..441d8786fcbc 100644
> > --- a/Documentation/kbuild/llvm.rst
> > +++ b/Documentation/kbuild/llvm.rst
> > @@ -71,10 +71,6 @@ recommend::
> >  
> >  	PATH=/path/to/llvm/:$PATH make LLVM=-14
> >  
> > -``LLVM=0`` is not the same as omitting ``LLVM`` altogether, it will behave like
> > -``LLVM=1``. If you only wish to use certain LLVM utilities, use their
> > -respective make variables.
> > -
> >  The same value used for ``LLVM=`` should be set for each invocation of ``make``
> >  if configuring and building via distinct commands. ``LLVM=`` should also be set
> >  as an environment variable when running scripts that will eventually run
> > 
> > -- 
> > 2.53.0
> > 

-- 
Nicolas

Re: [PATCH 0/2] kbuild: Follow-up to "Reject unexpected values for LLVM="

[Nicolas Schier]

On Thu, 26 Feb 2026 22:23:56 +0100, Thomas Weißschuh wrote:
> Some cleanups.
> 
> 

Applied to kbuild/linux.git (kbuild-for-next), thanks!

[1/2] Documentation/llvm: drop note about LLVM=0
      https://git.kernel.org/kbuild/c/8830b2e5
[2/2] tools/build: Reject unexpected values for LLVM=
      https://git.kernel.org/kbuild/c/7239ae53

Please look out for regression or issue reports or other follow up
comments, as they may result in the patch/series getting dropped,
reverted or modified (e.g. trailers). Patches applied to a
kbuild-*-unstable branch are accepted pending wider testing in
linux-next and any post-commit review; they will generally be moved
to the main branch (kbuild-next or kbuild-fixes) in a week if no
issues are found.

Best regards,
-- 
Nicolas