When trying to build the compile_commands.json target from an external
module's directory, the following error is displayed:

	make[1]: *** No rule to make target 'scripts/clang-tools/gen_compile_commands.py',
	needed by 'compile_commands.json'. Stop.

This appears to be because gen_compile_commands.py is looked up using
relative path, which doesn't exist from the module's source tree.
Prefixing the dependency with $(srctree) fixes the problem.

Signed-off-by: Alexandre Courbot <gnurou@gmail.com>
---
 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 8ad55d6e7b60..52d7dfe4212a 100644
--- a/Makefile
+++ b/Makefile
@@ -1980,7 +1980,7 @@ nsdeps: modules
 quiet_cmd_gen_compile_commands = GEN     $@
       cmd_gen_compile_commands = $(PYTHON3) $< -a $(AR) -o $@ $(filter-out $<, $(real-prereqs))
 
-$(extmod_prefix)compile_commands.json: scripts/clang-tools/gen_compile_commands.py \
+$(extmod_prefix)compile_commands.json: $(srctree)/scripts/clang-tools/gen_compile_commands.py \
 	$(if $(KBUILD_EXTMOD),, vmlinux.a $(KBUILD_VMLINUX_LIBS)) \
 	$(if $(CONFIG_MODULES), $(MODORDER)) FORCE
 	$(call if_changed,gen_compile_commands)
-- 
2.46.0

On Sat, Aug 3, 2024 at 9:52 PM Alexandre Courbot <gnurou@gmail.com> wrote:
>
> When trying to build the compile_commands.json target from an external
> module's directory, the following error is displayed:
>
>         make[1]: *** No rule to make target 'scripts/clang-tools/gen_compile_commands.py',
>         needed by 'compile_commands.json'. Stop.


Good catch.

But, to reproduce this, O= option is also needed, right?

e.g.

  $ make O=path/to/build/dir M=path/to/external/module/dir




> This appears to be because gen_compile_commands.py is looked up using
> relative path, which doesn't exist from the module's source tree.


The phrase "appears to be ..." is somewhat modest.


You can reword this to pin-point the first bad commit.


For example:

gen_compile_commands.py was previously looked up using a relative path
to $(srctree), but commit b1992c3772e6 ("kbuild: use $(src) instead of
$(srctree)/$(src) for source directory") stopped defining VPATH for
external module builds.



> Prefixing the dependency with $(srctree) fixes the problem.



This needs back-porting.


Please add this:

Fixes: b1992c3772e6 ("kbuild: use $(src) instead of $(srctree)/$(src)
for source directory")


Thanks.




> Signed-off-by: Alexandre Courbot <gnurou@gmail.com>
> ---
>  Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index 8ad55d6e7b60..52d7dfe4212a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1980,7 +1980,7 @@ nsdeps: modules
>  quiet_cmd_gen_compile_commands = GEN     $@
>        cmd_gen_compile_commands = $(PYTHON3) $< -a $(AR) -o $@ $(filter-out $<, $(real-prereqs))
>
> -$(extmod_prefix)compile_commands.json: scripts/clang-tools/gen_compile_commands.py \
> +$(extmod_prefix)compile_commands.json: $(srctree)/scripts/clang-tools/gen_compile_commands.py \
>         $(if $(KBUILD_EXTMOD),, vmlinux.a $(KBUILD_VMLINUX_LIBS)) \
>         $(if $(CONFIG_MODULES), $(MODORDER)) FORCE
>         $(call if_changed,gen_compile_commands)
> --
> 2.46.0
>


--
Best Regards

Masahiro Yamada

On Sat, Aug 3, 2024 at 10:47 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Sat, Aug 3, 2024 at 9:52 PM Alexandre Courbot <gnurou@gmail.com> wrote:
> >
> > When trying to build the compile_commands.json target from an external
> > module's directory, the following error is displayed:
> >
> >         make[1]: *** No rule to make target 'scripts/clang-tools/gen_compile_commands.py',
> >         needed by 'compile_commands.json'. Stop.
>
>
> Good catch.
>
> But, to reproduce this, O= option is also needed, right?
>
> e.g.
>
>   $ make O=path/to/build/dir M=path/to/external/module/dir

I am building the module as follows:

$ make -C ../linux/build M=$PWD modules compile_commands.json

The kernel itself was built with O=build though.

> > This appears to be because gen_compile_commands.py is looked up using
> > relative path, which doesn't exist from the module's source tree.
>
>
> The phrase "appears to be ..." is somewhat modest.
>
>
> You can reword this to pin-point the first bad commit.
>
>
> For example:
>
> gen_compile_commands.py was previously looked up using a relative path
> to $(srctree), but commit b1992c3772e6 ("kbuild: use $(src) instead of
> $(srctree)/$(src) for source directory") stopped defining VPATH for
> external module builds.

Thanks, that's much better. I should indeed have bisected to find the
source of the regression.

>
>
>
> > Prefixing the dependency with $(srctree) fixes the problem.
>
>
>
> This needs back-porting.
>
>
> Please add this:
>
> Fixes: b1992c3772e6 ("kbuild: use $(src) instead of $(srctree)/$(src)
> for source directory")

Done, and sent v2 as well.

Thank you!
Alex.

On Sun, Aug 4, 2024 at 2:51 PM Alexandre Courbot <gnurou@gmail.com> wrote:
>
> On Sat, Aug 3, 2024 at 10:47 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > On Sat, Aug 3, 2024 at 9:52 PM Alexandre Courbot <gnurou@gmail.com> wrote:
> > >
> > > When trying to build the compile_commands.json target from an external
> > > module's directory, the following error is displayed:
> > >
> > >         make[1]: *** No rule to make target 'scripts/clang-tools/gen_compile_commands.py',
> > >         needed by 'compile_commands.json'. Stop.
> >
> >
> > Good catch.
> >
> > But, to reproduce this, O= option is also needed, right?
> >
> > e.g.
> >
> >   $ make O=path/to/build/dir M=path/to/external/module/dir
>
> I am building the module as follows:
>
> $ make -C ../linux/build M=$PWD modules compile_commands.json


OK, this is equivalent to the command I gave.
You are building your external module
against the kernel built in a separate output directory.






-- 
Best Regards
Masahiro Yamada