diff mbox series

[2/2] kbuild: add more comments for KBUILD_NOCMDDEP=1

Message ID 20221229091501.916296-2-masahiroy@kernel.org (mailing list archive)
State New, archived
Headers show
Series [1/2] kbuild: rename cmd_$@ to savedcmd_$@ in *.cmd files | expand

Commit Message

Masahiro Yamada Dec. 29, 2022, 9:15 a.m. UTC 
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 <masahiroy@kernel.org>
---

 scripts/Kbuild.include | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Nicolas Schier Dec. 29, 2022, 2:11 p.m. UTC | #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 <masahiroy@kernel.org>
> ---
> 
>  scripts/Kbuild.include | 6 ++++++
>  1 file changed, 6 insertions(+)
> 

Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
diff mbox series

Patch

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