[PATCH v2 2/3] checksyscalls: only run when necessary

["Thomas Weißschuh" <linux@weissschuh.net>]

Currently checksyscalls.sh is unconditionally executed during each build.
Most of these executions are unnecessary.

Only run checksyscalls.sh if one of its inputs have changed.

This new logic does not work for the multiple invocations done for MIPS.
The effect is that checksyscalls.sh is still executed unconditionally.
However this is not worse than before.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 Kbuild                   | 12 +++++++++---
 scripts/checksyscalls.sh |  5 +++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/Kbuild b/Kbuild
index 13324b4bbe23..515cc6a27477 100644
--- a/Kbuild
+++ b/Kbuild
@@ -47,12 +47,18 @@ $(rq-offsets-file): kernel/sched/rq-offsets.s FORCE
 
 # Check for missing system calls
 
+missing-syscalls-file := .tmp_missing-syscalls
+
+targets += $(missing-syscalls-file)
+
 quiet_cmd_syscalls = CALL    $<
-      cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
+      cmd_syscalls = DEPFILE=$(depfile) $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags); touch $@
+
+$(missing-syscalls-file): scripts/checksyscalls.sh $(rq-offsets-file) FORCE
+	$(call if_changed_dep,syscalls)
 
 PHONY += missing-syscalls
-missing-syscalls: scripts/checksyscalls.sh $(rq-offsets-file)
-	$(call cmd,syscalls)
+missing-syscalls: $(missing-syscalls-file)
 
 # Check the manual modification of atomic headers
 
diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
index 9becaf8d7b78..a6d0882f07e1 100755
--- a/scripts/checksyscalls.sh
+++ b/scripts/checksyscalls.sh
@@ -273,3 +273,8 @@ syscall_list() {
 
 (ignore_list && syscall_list ${reference_table}) | \
 $* -Wno-error -Wno-unused-macros -E -x c - > /dev/null
+
+# For fixdep
+if [ -n "${DEPFILE}" ]; then
+	echo "${0}: ${0} ${reference_table}" >> "${DEPFILE}"
+fi

-- 
2.53.0