The cmd-check for KBUILD_NOCMDDEP=1 may not be clear until you see
commit c4d5ee13984f ("kbuild: make KBUILD_NOCMDDEP=1 handle empty
built-in.o").
When a phony target (i.e. FORCE) is the only prerequisite, Kbuild
uses a tricky way to detect that the target does not exist.
Add more comments.
Signed-off-by: Masahiro Yamada <[email protected]>
---
scripts/Kbuild.include | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 1a7514f49089..4648ab8f11d4 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -170,9 +170,13 @@ cmd = @$(if $(cmd_$(1)),set -e; $($(quiet)log_print) $(delete-on-interrupt) $(cm
ifneq ($(KBUILD_NOCMDDEP),1)
# Check if both commands are the same including their order. Result is empty
# string if equal. User may override this check using make KBUILD_NOCMDDEP=1
+# If the target does not exist, the *.cmd file should not be included so
+# $(savedcmd_$@) gets empty. Then, target will be built even if $(newer-prereqs)
+# happens to become empty.
cmd-check = $(filter-out $(subst $(space),$(space_escape),$(strip $(savedcmd_$@))), \
$(subst $(space),$(space_escape),$(strip $(cmd_$1))))
else
+# We still need to detect missing targets.
cmd-check = $(if $(strip $(savedcmd_$@)),,1)
endif
@@ -186,6 +190,8 @@ make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1))))
# Find any prerequisites that are newer than target or that do not exist.
# PHONY targets skipped in both cases.
+# If there is no prerequisite other than phony targets, $(newer-prereqs) becomes
+# empty even if the target does not exist. cmd-check saves this corner case.
newer-prereqs = $(filter-out $(PHONY),$?)
# It is a typical mistake to forget the FORCE prerequisite. Check it here so
--
2.34.1
On Thu, Dec 29, 2022 at 06:15:01PM +0900 Masahiro Yamada wrote:
> The cmd-check for KBUILD_NOCMDDEP=1 may not be clear until you see
> commit c4d5ee13984f ("kbuild: make KBUILD_NOCMDDEP=1 handle empty
> built-in.o").
>
> When a phony target (i.e. FORCE) is the only prerequisite, Kbuild
> uses a tricky way to detect that the target does not exist.
>
> Add more comments.
>
> Signed-off-by: Masahiro Yamada <[email protected]>
> ---
>
> scripts/Kbuild.include | 6 ++++++
> 1 file changed, 6 insertions(+)
>
Reviewed-by: Nicolas Schier <[email protected]>
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