[PATCH] kbuild: fix rebuild of generic syscall headers

[Masahiro Yamada <masahiroy@kernel.org>]

Commit fbb5c0606fa4 ("kbuild: add syscall table generation to
scripts/Makefile.asm-headers") started to generate syscall headers
for architectures using generic syscalls.

However, these headers are always rebuilt using GNU Make 4.4.1 or newer.

When using GNU Make 4.4 or older, these headers are not rebuilt when the
command to generate them is changed, despite the use of the if_changed
macro.

scripts/Makefile.asm-headers now uses FORCE, but it is not marked as
.PHONY. To handle the command line change correctly, .*.cmd files must
be included.

Fixes: fbb5c0606fa4 ("kbuild: add syscall table generation to scripts/Makefile.asm-headers")
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/lkml/CAHk-=wibB7SvXnUftBgAt+4-3vEKRpvEgBeDEH=i=j2GvDitoA@mail.gmail.com/
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 scripts/Makefile.asm-headers | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/scripts/Makefile.asm-headers b/scripts/Makefile.asm-headers
index 6b8e8318e810..8a4856e74180 100644
--- a/scripts/Makefile.asm-headers
+++ b/scripts/Makefile.asm-headers
@@ -87,12 +87,20 @@ $(obj)/unistd_compat_%.h: $(syscalltbl) $(syshdr) FORCE
 $(obj)/syscall_table_%.h: $(syscalltbl) $(systbl) FORCE
 	$(call if_changed,systbl)
 
+targets := $(syscall-y)
+
 # Create output directory. Skip it if at least one old header exists
 # since we know the output directory already exists.
 ifeq ($(old-headers),)
 $(shell mkdir -p $(obj))
 endif
 
+PHONY += FORCE
+
 FORCE:
 
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
 .PHONY: $(PHONY)
-- 
2.43.0