linux-kernel - Re: [PATCH v4 2/3] tools build: Avoid circular .fixdep-in.o.cmd issues

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Message-ID: <ZpYngEl9XKumuow5@krava>
Date: Tue, 16 Jul 2024 09:55:44 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Brian Norris <briannorris@...omium.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Thomas Richter <tmricht@...ux.ibm.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>, bpf@...r.kernel.org,
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v4 2/3] tools build: Avoid circular .fixdep-in.o.cmd
 issues

On Mon, Jul 15, 2024 at 01:32:43PM -0700, Brian Norris wrote:
> The 'fixdep' tool is used to post-process dependency files for various
> reasons, and it runs after every object file generation command. This
> even includes 'fixdep' itself.
> 
> In Kbuild, this isn't actually a problem, because it uses a single
> command to generate fixdep (a compile-and-link command on fixdep.c), and
> afterward runs the fixdep command on the accompanying .fixdep.cmd file.
> 
> In tools/ builds (which notably is maintained separately from Kbuild),
> fixdep is generated in several phases:
> 
>  1. fixdep.c -> fixdep-in.o
>  2. fixdep-in.o -> fixdep
> 
> Thus, fixdep is not available in the post-processing for step 1, and
> instead, we generate .cmd files that look like:
> 
>   ## from tools/objtool/libsubcmd/.fixdep.o.cmd
>   # cannot find fixdep (/path/to/linux/tools/objtool/libsubcmd//fixdep)
>   [...]
> 
> These invalid .cmd files are benign in some respects, but cause problems
> in others (such as the linked reports).
> 
> Because the tools/ build system is rather complicated in its own right
> (and pointedly different than Kbuild), I choose to simply open-code the
> rule for building fixdep, and avoid the recursive-make indirection that
> produces the problem in the first place.
> 
> Link: https://lore.kernel.org/all/Zk-C5Eg84yt6_nml@google.com/
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
> 
> (no changes since v3)
> 
> Changes in v3:
>  - Drop unnecessary tools/build/Build

Acked-by: Jiri Olsa <jolsa@...nel.org>

so usually Arnaldo takes changes for tools/build, Arnaldo, could you please take a look?
but still there'are the tools/lib/bpf bits..

thanks,
jirka

> 
>  tools/build/Build    |  3 ---
>  tools/build/Makefile | 11 ++---------
>  2 files changed, 2 insertions(+), 12 deletions(-)
>  delete mode 100644 tools/build/Build
> 
> diff --git a/tools/build/Build b/tools/build/Build
> deleted file mode 100644
> index 76d1a4960973..000000000000
> --- a/tools/build/Build
> +++ /dev/null
> @@ -1,3 +0,0 @@
> -hostprogs := fixdep
> -
> -fixdep-y := fixdep.o
> diff --git a/tools/build/Makefile b/tools/build/Makefile
> index 17cdf01e29a0..fea3cf647f5b 100644
> --- a/tools/build/Makefile
> +++ b/tools/build/Makefile
> @@ -43,12 +43,5 @@ ifneq ($(wildcard $(TMP_O)),)
>  	$(Q)$(MAKE) -C feature OUTPUT=$(TMP_O) clean >/dev/null
>  endif
>  
> -$(OUTPUT)fixdep-in.o: FORCE
> -	$(Q)$(MAKE) $(build)=fixdep
> -
> -$(OUTPUT)fixdep: $(OUTPUT)fixdep-in.o
> -	$(QUIET_LINK)$(HOSTCC) $(KBUILD_HOSTLDFLAGS) -o $@ $<
> -
> -FORCE:
> -
> -.PHONY: FORCE
> +$(OUTPUT)fixdep: $(srctree)/tools/build/fixdep.c
> +	$(QUIET_CC)$(HOSTCC) $(KBUILD_HOSTLDFLAGS) -o $@ $<
> -- 
> 2.45.2.993.g49e7a77208-goog
> 
>