Re: [PATCH 1/1] kbuild: record real-prereqs in .cmd files

Luis Augenstein <[email protected]> Fri, 21 Aug 2026 21:57:03 +0200

Newsgroups	org.kernel.vger.linux-kbuild,org.kernel.vger.linux-kernel
Message-ID	<[email protected]>


On 8/18/26 21:51, Nathan Chancellor wrote:
> Sashiko has a comment that this produces different results based on a
> clean versus incremental build:
> 
>    https://sashiko.dev/#/patchset/59032
> 
> I can reproduce this with:
> 
>    $ make -skj"$(nproc)" ARCH=x86_64 mrproper defconfig lib/oid_registry.o
> 
>    $ grep -n oid_registry_data lib/.oid_registry.o.cmd
>    3:make_prereqs_lib/oid_registry.o := lib/oid_registry.c lib/oid_registry_data.c
>    1111:  lib/oid_registry_data.c \
> 
>    $ touch lib/oid_registry.c
> 
>    $ make -skj"$(nproc)" ARCH=x86_64 lib/oid_registry.o
> 
>    $ grep -n oid_registry_data lib/.oid_registry.o.cmd
>    1111:  lib/oid_registry_data.c \
> 
> As this is just metadata for external tools (i.e., it does not get
> consumed by Kbuild again), we could just require them to filter
> duplicates after the fact?

True, some Make prerequisites also appear in deps_*, so the filter
dropped them from make_prereqs_* on incremental builds.

However, we cannot just remove the filter. After the .cmd is included,
$(real-prereqs) contains $(deps_$@), so the whole deps_* list would
show up in make_prereqs_* on a rebuild.

We could move the filter into fixdep and filter based on the new .d 
file, so the overlap is removed already on a clean build.

thanks,
Luis

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Luis Augenstein * [email protected] * +4915225275761
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