linux-kernel - [PATCH] kbuild: mark "FORCE" target as secondary

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Message-Id: <20240717124253.2275084-1-arnd@kernel.org>
Date: Wed, 17 Jul 2024 14:42:44 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Arnd Bergmann <arnd@...db.de>
Cc: linux-kbuild@...r.kernel.org,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] kbuild: mark "FORCE" target as secondary

From: Arnd Bergmann <arnd@...db.de>

Starting with make-4.4.1, Kbuild uses the special .NOTINTERMEDIATE
target to mark all targets as not intermediate, which slightly changes
the behavior compared to older versions of make.

This causes a build regression with my change to the system call table
scripts now in scripts/Makefile.asm-headers, forcing a rebuild of the
generated files with every make invocation and effectively breaking
incremental builds.

I have narrowed down the change in behavior to the way that the
'FORCE' target is treated: If this is marked as not intermediate,
the $(if_changed) macro always evaluates it as a missing prerequisite,
but if it is marked as .SECONDARY, it works like before.

Cc: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org
Fixes: 875ef1a57f32 ("kbuild: use .NOTINTERMEDIATE for future GNU Make versions")
Fixes: fbb5c0606fa4 ("kbuild: add syscall table generation to scripts/Makefile.asm-headers")
Closes: https://lore.kernel.org/lkml/91b10591-1554-4860-8843-01c6cfd7de13@app.fastmail.com/T/#m4c979c42d0c086f616e41b4ca76f2873902b8a25
Signed-off-by: Arnd Bergmann <arnd@...db.de>
----
I'm still a bit confused by the way this works in detail, hopefully
Masahiro Yamada can either confirm that this is a correct fix or provide
a better one.
---
 scripts/Kbuild.include | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index faf37bafa3f8..aa1ffaeb8fc0 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -267,6 +267,7 @@ endif
 # deleted files.
 ifneq ($(and $(filter notintermediate, $(.FEATURES)),$(filter-out 4.4,$(MAKE_VERSION))),)
 .NOTINTERMEDIATE:
+.SECONDARY: FORCE
 else
 .SECONDARY:
 endif
-- 
2.39.2