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tools build: Avoid circular .fixdep-in.o.cmd issues

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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.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Link: https://lore.kernel.org/all/Zk-C5Eg84yt6_nml@google.com/
Link: https://lore.kernel.org/r/20240715203325.3832977-3-briannorris@chromium.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Brian Norris 2024-07-15 13:32:43 -07:00 committed by Arnaldo Carvalho de Melo
parent 96f30c8f0a
commit ea974028a0
2 changed files with 2 additions and 12 deletions
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3
tools/build/Build
View File

@ -1,3 +0,0 @@
hostprogs := fixdep
fixdep-y := fixdep.o

11
tools/build/Makefile
View File

@ -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 $@ $<