linux-kernel - Re: tools build: Fix fixdep dependencies

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Message-ID: <c1d395c6-2d3b-4504-befe-6e67c7ed96fc@leemhuis.info>
Date: Sat, 18 Oct 2025 07:12:02 +0200
From: Thorsten Leemhuis <linux@...mhuis.info>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: linux-kernel@...r.kernel.org, Arthur Marsh
 <arthur.marsh@...ernode.on.net>, x86@...nel.org
Subject: Re: tools build: Fix fixdep dependencies

On 10/16/25 11:53, tip-bot2 for Josh Poimboeuf wrote:
> The following commit has been merged into the objtool/core branch of tip:
> 
> Commit-ID:     a808a2b35f66658e6c49dc98b55a33fa1079fe72
> Gitweb:        https://git.kernel.org/tip/a808a2b35f66658e6c49dc98b55a33fa1079fe72
> Author:        Josh Poimboeuf <jpoimboe@...nel.org>
> AuthorDate:    Sun, 02 Mar 2025 17:01:42 -08:00
> Committer:     Josh Poimboeuf <jpoimboe@...nel.org>
> CommitterDate: Tue, 14 Oct 2025 14:45:20 -07:00
> 
> tools build: Fix fixdep dependencies
> 
> The tools version of fixdep has broken dependencies.  It doesn't get
> rebuilt if the host compiler or headers change.

My daily -next rebuilds based on the Fedora rawhide srpm failed due to
this patch while building perf:

make[4]: *** No rule to make target '/builddir/build/BUILD/kernel-6.18.0-build/kernel-next-20251017/linux-6.18.0-0.0.next.20251017.420.vanilla.fc44.aarch64/tools/perf/libsubcmd/fixdep'.  Stop.
make[3]: *** [/builddir/build/BUILD/kernel-6.18.0-build/kernel-next-20251017/linux-6.18.0-0.0.next.20251017.420.vanilla.fc44.aarch64/tools/build/Makefile.include:15: fixdep] Error 2
make[2]: *** [Makefile.perf:981: /builddir/build/BUILD/kernel-6.18.0-build/kernel-next-20251017/linux-6.18.0-0.0.next.20251017.420.vanilla.fc44.aarch64/tools/perf/libsubcmd/libsubcmd.a] Error 2
make[2]: *** Waiting for unfinished jobs....

Full log: https://download.copr.fedorainfracloud.org/results/@kernel-vanilla/next/fedora-rawhide-aarch64/09700031-next-next-all/builder-live.log.gz

Happened on ppc64 and s390x, too (and likely on x86_64, too, but that
failed earlier during the build due to an unrelated problem).

Reverting this change fixed the problem.

Ciao, Thorsten

 
> Build fixdep with the tools kbuild infrastructure, so fixdep runs on
> itself.  Due to the recursive dependency, its dependency file is
> incomplete the very first time it gets built.  In that case build it a
> second time to achieve fixdep inception.
> 
> Reported-by: Arthur Marsh <arthur.marsh@...ernode.on.net>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>  tools/build/Build    |  2 ++
>  tools/build/Makefile | 23 +++++++++++++++++++++--
>  2 files changed, 23 insertions(+), 2 deletions(-)
>  create mode 100644 tools/build/Build
> 
> diff --git a/tools/build/Build b/tools/build/Build
> new file mode 100644
> index 0000000..1c7e598
> --- /dev/null
> +++ b/tools/build/Build
> @@ -0,0 +1,2 @@
> +hostprogs	:= fixdep
> +fixdep-y	:= fixdep.o
> diff --git a/tools/build/Makefile b/tools/build/Makefile
> index 63ef218..a5b3c29 100644
> --- a/tools/build/Makefile
> +++ b/tools/build/Makefile
> @@ -37,5 +37,24 @@ ifneq ($(wildcard $(TMP_O)),)
>  	$(Q)$(MAKE) -C feature OUTPUT=$(TMP_O) clean >/dev/null
>  endif
>  
> -$(OUTPUT)fixdep: $(srctree)/tools/build/fixdep.c
> -	$(QUIET_CC)$(HOSTCC) $(KBUILD_HOSTCFLAGS) $(KBUILD_HOSTLDFLAGS) -o $@ $<
> +include $(srctree)/tools/build/Makefile.include
> +
> +FIXDEP		:= $(OUTPUT)fixdep
> +FIXDEP_IN	:= $(OUTPUT)fixdep-in.o
> +
> +# To track fixdep's dependencies properly, fixdep needs to run on itself.
> +# Build it twice the first time.
> +$(FIXDEP_IN): FORCE
> +	$(Q)if [ ! -f $(FIXDEP) ]; then						\
> +		$(MAKE) $(build)=fixdep HOSTCFLAGS="$(KBUILD_HOSTCFLAGS)";	\
> +		rm -f $(FIXDEP).o;						\
> +	fi
> +	$(Q)$(MAKE) $(build)=fixdep HOSTCFLAGS="$(KBUILD_HOSTCFLAGS)"
> +
> +
> +$(FIXDEP): $(FIXDEP_IN)
> +	$(QUIET_LINK)$(HOSTCC) $(FIXDEP_IN) $(KBUILD_HOSTLDFLAGS) -o $@
> +
> +FORCE:
> +
> +.PHONY: FORCE
>