[PATCH v2 0/3] checksyscalls: only run when necessary

[PATCH v2 0/3] checksyscalls: only run when necessary

[Thomas Weißschuh]

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.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Changes in v2:
- Also send to kbuild maintainers
- Link to v1: https://patch.msgid.link/20260303-kbuild-missing-syscalls-v1-0-3b4d69b68c75@weissschuh.net

---
Thomas Weißschuh (3):
      checksyscalls: move path to reference table to a variable
      checksyscalls: only run when necessary
      checksyscalls: move instance functionality into generic code

 Kbuild                   | 14 ++++++++++----
 arch/mips/Makefile       |  6 ++----
 scripts/checksyscalls.sh |  9 ++++++++-
 3 files changed, 20 insertions(+), 9 deletions(-)
---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260212-kbuild-missing-syscalls-e328de3c4b54

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

[PATCH v2 1/3] checksyscalls: move path to reference table to a variable

[Thomas Weißschuh]

An upcoming patch will need to reuse this path.

Move it into a reusable variable.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 scripts/checksyscalls.sh | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
index 1e5d2eeb726d..9becaf8d7b78 100755
--- a/scripts/checksyscalls.sh
+++ b/scripts/checksyscalls.sh
@@ -10,6 +10,8 @@
 # checksyscalls.sh gcc gcc-options
 #
 
+reference_table="$(dirname $0)/../arch/x86/entry/syscalls/syscall_32.tbl"
+
 ignore_list() {
 cat << EOF
 #include <asm/types.h>
@@ -269,5 +271,5 @@ syscall_list() {
 	done
 }
 
-(ignore_list && syscall_list $(dirname $0)/../arch/x86/entry/syscalls/syscall_32.tbl) | \
+(ignore_list && syscall_list ${reference_table}) | \
 $* -Wno-error -Wno-unused-macros -E -x c - > /dev/null

-- 
2.53.0

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

[Thomas Weißschuh]

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

[PATCH v2 3/3] checksyscalls: move instance functionality into generic code

[Thomas Weißschuh]

On MIPS the checksyscalls.sh script may be executed multiple times.
Currently these multiple executions are executed on each build as kbuild
see that the commands have changed each time.

Use a dedicated stamp file for each different invocation to avoid the
spurious executions.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 Kbuild             | 4 ++--
 arch/mips/Makefile | 6 ++----
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/Kbuild b/Kbuild
index 515cc6a27477..fb547bc5ff41 100644
--- a/Kbuild
+++ b/Kbuild
@@ -47,11 +47,11 @@ $(rq-offsets-file): kernel/sched/rq-offsets.s FORCE
 
 # Check for missing system calls
 
-missing-syscalls-file := .tmp_missing-syscalls
+missing-syscalls-file := .tmp_missing-syscalls$(missing_syscalls_instance)
 
 targets += $(missing-syscalls-file)
 
-quiet_cmd_syscalls = CALL    $<
+quiet_cmd_syscalls = CALL    $< $(if $(missing_syscalls_instance),for $(missing_syscalls_instance))
       cmd_syscalls = DEPFILE=$(depfile) $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags); touch $@
 
 $(missing-syscalls-file): scripts/checksyscalls.sh $(rq-offsets-file) FORCE
diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index d9057e29bc62..6705fa5d9211 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -421,12 +421,10 @@ CLEAN_FILES += vmlinux.32 vmlinux.64
 
 archprepare:
 ifdef CONFIG_MIPS32_N32
-	@$(kecho) '  Checking missing-syscalls for N32'
-	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_flags="-mabi=n32"
+	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_instance="N32" missing_syscalls_flags="-mabi=n32"
 endif
 ifdef CONFIG_MIPS32_O32
-	@$(kecho) '  Checking missing-syscalls for O32'
-	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_flags="-mabi=32"
+	$(Q)$(MAKE) $(build)=. missing-syscalls missing_syscalls_instance="O32" missing_syscalls_flags="-mabi=32"
 endif
 
 install:

-- 
2.53.0

Re: [PATCH v2 3/3] checksyscalls: move instance functionality into generic code

[Nicolas Schier]

On Tue, 24 Mar 2026 18:16:47 +0100, Thomas Weißschuh <linux@weissschuh.net> wrote:
> diff --git a/Kbuild b/Kbuild
> index 515cc6a27477..fb547bc5ff41 100644
> --- a/Kbuild
> +++ b/Kbuild
> @@ -47,11 +47,11 @@ $(rq-offsets-file): kernel/sched/rq-offsets.s FORCE
>  
>  # Check for missing system calls
>  
> -missing-syscalls-file := .tmp_missing-syscalls
> +missing-syscalls-file := .tmp_missing-syscalls$(missing_syscalls_instance)
>  
>  targets += $(missing-syscalls-file)
>  
> -quiet_cmd_syscalls = CALL    $<
> +quiet_cmd_syscalls = CALL    $< $(if $(missing_syscalls_instance),for $(missing_syscalls_instance))

Nice solution!

$(addprefix) shortens a bit here:

quiet_cmd_syscalls = CALL    $< $(addprefix for ,$(missing_syscalls_instance))

-- 
Nicolas

Re: [PATCH v2 0/3] checksyscalls: only run when necessary

[Arnd Bergmann]

On Tue, Mar 24, 2026, at 18:16, Thomas Weißschuh wrote:
> 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.
>
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

Nice series!

Acked-by: Arnd Bergmann <arnd@arndb.de>

At some point, we should revisit the syscall table use and just have
a shared table across all architectures for the syscalls above 402,
which are almost identical already. That requires a bit of scripting
but will let us just drop the checksyscalls script that hasn't
been all that useful for a while now.

      Arnd

Re: [PATCH v2 0/3] checksyscalls: only run when necessary

[Nicolas Schier]

On 2026-03-24 18:29:13+01:00, Arnd Bergmann wrote:
> On Tue, Mar 24, 2026, at 18:16, Thomas Weißschuh wrote:
> 
> > 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.
> >
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> 
> Nice series!
> 

yes, nice series with good ideas.  Thanks!


Reviewed-by: Nicolas Schier <nsc@kernel.org>