[PATCH 00/13] selftests: Fix problems seen when building with -Werror

[PATCH 00/13] selftests: Fix problems seen when building with -Werror

[Guenter Roeck]

This series fixes build errors observed when trying to build selftests
with -Werror.

----------------------------------------------------------------
Guenter Roeck (13):
      clone3: clone3_cap_checkpoint_restore: Fix build errors seen with -Werror
      selftests: ntsync: Fix build errors -seen with -Werror
      selftests/filesystems: fclog: Fix build errors seen with -Werror
      selftests/filesystems: file_stressor: Fix build error seen with -Werror
      selftests/filesystems: anon_inode_test: Fix build error seen with -Werror
      selftest: af_unix: Support compilers without flex-array-member-not-at-end support
      selftest/futex: Comment out test_futex_mpol
      selftests: net: netlink-dumps: Avoid uninitialized variable error
      selftests/seccomp: Fix build error seen with -Werror
      selftests: net: Work around build error seen with -Werror
      selftests/fs/mount-notify: Fix build failure seen with -Werror
      selftests/fs/mount-notify-ns: Fix build failures seen with -Werror
      selftests: net: tfo: Fix build error seen with -Werror

 tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c      | 4 ----
 tools/testing/selftests/drivers/ntsync/ntsync.c                     | 4 ++--
 tools/testing/selftests/filesystems/anon_inode_test.c               | 1 +
 tools/testing/selftests/filesystems/fclog.c                         | 1 +
 tools/testing/selftests/filesystems/file_stressor.c                 | 2 --
 .../testing/selftests/filesystems/mount-notify/mount-notify_test.c  | 3 ++-
 .../selftests/filesystems/mount-notify/mount-notify_test_ns.c       | 3 ++-
 tools/testing/selftests/futex/functional/futex_numa_mpol.c          | 2 ++
 tools/testing/selftests/net/af_unix/Makefile                        | 2 +-
 tools/testing/selftests/net/lib/ksft.h                              | 6 ++++--
 tools/testing/selftests/net/netlink-dumps.c                         | 2 +-
 tools/testing/selftests/net/tfo.c                                   | 3 ++-
 tools/testing/selftests/seccomp/seccomp_bpf.c                       | 3 ++-
 13 files changed, 20 insertions(+), 16 deletions(-)

[PATCH 01/13] clone3: clone3_cap_checkpoint_restore: Fix build errors seen with -Werror

[Guenter Roeck]

Fix:

clone3_cap_checkpoint_restore.c:56:7: error: unused variable 'ret'
   56 |                 int ret;
      |                     ^~~
clone3_cap_checkpoint_restore.c:57:8: error: unused variable 'tmp'
   57 |                 char tmp = 0;
      |                      ^~~
clone3_cap_checkpoint_restore.c:138:6: error: unused variable 'ret'
  138 |         int ret = 0;

by removing the unused variables.

Fixes: 1d27a0be16d6 ("selftests: add clone3() CAP_CHECKPOINT_RESTORE test")
Cc: Adrian Reber <areber@redhat.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 .../testing/selftests/clone3/clone3_cap_checkpoint_restore.c  | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
index 3c196fa86c99..976e92c259fc 100644
--- a/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
+++ b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
@@ -53,9 +53,6 @@ static int call_clone3_set_tid(struct __test_metadata *_metadata,
 	}
 
 	if (pid == 0) {
-		int ret;
-		char tmp = 0;
-
 		TH_LOG("I am the child, my PID is %d (expected %d)", getpid(), set_tid[0]);
 
 		if (set_tid[0] != getpid())
@@ -135,7 +132,6 @@ TEST(clone3_cap_checkpoint_restore)
 {
 	pid_t pid;
 	int status;
-	int ret = 0;
 	pid_t set_tid[1];
 
 	test_clone3_supported();
-- 
2.43.0

[PATCH 02/13] selftests: ntsync: Fix build errors -seen with -Werror

[Guenter Roeck]

Fix

ntsync.c:1286:20: error: call to undeclared function 'gettid';
	ISO C99 and later do not support implicit function declarations
 1286 |         wait_args.owner = gettid();
      |                           ^
ntsync.c:1280:8: error: unused variable 'index'
 1280 |         __u32 index, count, i;
      |               ^~~~~
ntsync.c:1281:6: error: unused variable 'ret'
 1281 |         int ret;

by adding the missing include file and removing the unused variables.

Fixes: a22860e57b54 ("selftests: ntsync: Add a stress test for contended waits.")
Cc: Elizabeth Figura <zfigura@codeweavers.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/drivers/ntsync/ntsync.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/drivers/ntsync/ntsync.c b/tools/testing/selftests/drivers/ntsync/ntsync.c
index 3aad311574c4..d3df94047e4d 100644
--- a/tools/testing/selftests/drivers/ntsync/ntsync.c
+++ b/tools/testing/selftests/drivers/ntsync/ntsync.c
@@ -11,6 +11,7 @@
 #include <fcntl.h>
 #include <time.h>
 #include <pthread.h>
+#include <unistd.h>
 #include <linux/ntsync.h>
 #include "../../kselftest_harness.h"
 
@@ -1277,8 +1278,7 @@ static int stress_device, stress_start_event, stress_mutex;
 static void *stress_thread(void *arg)
 {
 	struct ntsync_wait_args wait_args = {0};
-	__u32 index, count, i;
-	int ret;
+	__u32 count, i;
 
 	wait_args.timeout = UINT64_MAX;
 	wait_args.count = 1;
-- 
2.43.0

[PATCH 03/13] selftests/filesystems: fclog: Fix build errors seen with -Werror

[Guenter Roeck]

Fix

fclog.c:37:21: error: call to undeclared function 'open'
fclog.c:37:47: error: use of undeclared identifier 'O_RDONLY'; did you mean 'MS_RDONLY'?
fclog.c:37:56: error: use of undeclared identifier 'O_CLOEXEC'

by adding the missing include file.

Fixes: df579e471111b ("selftests/filesystems: add basic fscontext log tests")
Cc: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/filesystems/fclog.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/filesystems/fclog.c b/tools/testing/selftests/filesystems/fclog.c
index 912a8b755c3b..d7cc3aaa8672 100644
--- a/tools/testing/selftests/filesystems/fclog.c
+++ b/tools/testing/selftests/filesystems/fclog.c
@@ -6,6 +6,7 @@
 
 #include <assert.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <sched.h>
 #include <stdio.h>
 #include <stdlib.h>
-- 
2.43.0

[PATCH 04/13] selftests/filesystems: file_stressor: Fix build error seen with -Werror

[Guenter Roeck]

Fix

file_stressor.c:112:9: error: unused variable 'pid_self'

by dropping the unused variable.

Fixes: aab154a442f9b ("selftests: add file SLAB_TYPESAFE_BY_RCU recycling stressor")
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/filesystems/file_stressor.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/tools/testing/selftests/filesystems/file_stressor.c b/tools/testing/selftests/filesystems/file_stressor.c
index 01dd89f8e52f..4f314270298d 100644
--- a/tools/testing/selftests/filesystems/file_stressor.c
+++ b/tools/testing/selftests/filesystems/file_stressor.c
@@ -109,8 +109,6 @@ FIXTURE_TEARDOWN(file_stressor)
 TEST_F_TIMEOUT(file_stressor, slab_typesafe_by_rcu, 900 * 2)
 {
 	for (int i = 0; i < self->nr_procs; i++) {
-		pid_t pid_self;
-
 		self->pids_openers[i] = fork();
 		ASSERT_GE(self->pids_openers[i], 0);
 
-- 
2.43.0

[PATCH 05/13] selftests/filesystems: anon_inode_test: Fix build error seen with -Werror

[Guenter Roeck]

Fix

anon_inode_test.c:45:12: error: call to undeclared function 'execveat'

by adding the missing include file.

Fixes: f8ca403ae77cb ("selftests/filesystems: add exec() test for anonymous inodes")
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
This patch does not fix:

anon_inode_test.c: In function ‘anon_inode_no_exec’:
anon_inode_test.c:46:19: error: argument 3 null where non-null expected

because I have no idea how to do that.

 tools/testing/selftests/filesystems/anon_inode_test.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/filesystems/anon_inode_test.c b/tools/testing/selftests/filesystems/anon_inode_test.c
index 73e0a4d4fb2f..5ddcfd2927f9 100644
--- a/tools/testing/selftests/filesystems/anon_inode_test.c
+++ b/tools/testing/selftests/filesystems/anon_inode_test.c
@@ -4,6 +4,7 @@
 
 #include <fcntl.h>
 #include <stdio.h>
+#include <unistd.h>
 #include <sys/stat.h>
 
 #include "../kselftest_harness.h"
-- 
2.43.0

[PATCH 06/13] selftest: af_unix: Support compilers without flex-array-member-not-at-end support

[Guenter Roeck]

Fix:

gcc: error: unrecognized command-line option ‘-Wflex-array-member-not-at-end’

by making the compiler option dependent on its support.

Fixes: 1838731f1072c ("selftest: af_unix: Add -Wall and -Wflex-array-member-not-at-end to CFLAGS.")
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/net/af_unix/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile
index 528d14c598bb..04e82a8d21db 100644
--- a/tools/testing/selftests/net/af_unix/Makefile
+++ b/tools/testing/selftests/net/af_unix/Makefile
@@ -1,4 +1,4 @@
-CFLAGS += $(KHDR_INCLUDES) -Wall -Wflex-array-member-not-at-end
+CFLAGS += $(KHDR_INCLUDES) -Wall $(call cc-option,-Wflex-array-member-not-at-end)
 
 TEST_GEN_PROGS := \
 	diag_uid \
-- 
2.43.0

[PATCH 07/13] selftest/futex: Comment out test_futex_mpol

[Guenter Roeck]

test_futex_mpol() is not called, resulting in

futex_numa_mpol.c:134:13: error: ‘test_futex_mpol’ defined but not used

if built with -Werror. Disable the function but keep it in case it was
supposed to be used.

Fixes: d35ca2f64272 ("selftests/futex: Refactor futex_numa_mpol with kselftest_harness.h")
Cc: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/futex/functional/futex_numa_mpol.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/futex/functional/futex_numa_mpol.c b/tools/testing/selftests/futex/functional/futex_numa_mpol.c
index d037a3f10ee8..8e3d17d66684 100644
--- a/tools/testing/selftests/futex/functional/futex_numa_mpol.c
+++ b/tools/testing/selftests/futex/functional/futex_numa_mpol.c
@@ -131,10 +131,12 @@ static void test_futex(void *futex_ptr, int err_value)
 	__test_futex(futex_ptr, err_value, FUTEX2_SIZE_U32 | FUTEX_PRIVATE_FLAG | FUTEX2_NUMA);
 }
 
+#ifdef NOTUSED
 static void test_futex_mpol(void *futex_ptr, int err_value)
 {
 	__test_futex(futex_ptr, err_value, FUTEX2_SIZE_U32 | FUTEX_PRIVATE_FLAG | FUTEX2_NUMA | FUTEX2_MPOL);
 }
+#endif
 
 TEST(futex_numa_mpol)
 {
-- 
2.43.0

[PATCH 08/13] selftests: net: netlink-dumps: Avoid uninitialized variable error

[Guenter Roeck]

Building netlink-dumps with -Werror results in

netlink-dumps.c: In function ‘dump_extack’:
../kselftest_harness.h:788:35: error: ‘ret’ may be used uninitialized

Problem is that the loop which initializes 'ret' may exit early without
initializing the variable if recv() returns an error. Always initialize
'ret' to solve the problem.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/net/netlink-dumps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/netlink-dumps.c b/tools/testing/selftests/net/netlink-dumps.c
index 7618ebe528a4..f4fc0c9910f2 100644
--- a/tools/testing/selftests/net/netlink-dumps.c
+++ b/tools/testing/selftests/net/netlink-dumps.c
@@ -112,7 +112,7 @@ static const struct {
 TEST(dump_extack)
 {
 	int netlink_sock;
-	int i, cnt, ret;
+	int i, cnt, ret = FOUND_ERR;
 	char buf[8192];
 	int one = 1;
 	ssize_t n;
-- 
2.43.0

[PATCH 09/13] selftests/seccomp: Fix build error seen with -Werror

[Guenter Roeck]

Fix:

seccomp_bpf.c: In function ‘UPROBE_setup’:
seccomp_bpf.c:5175:74: error: pointer type mismatch in conditional expression

by type casting the argument to get_uprobe_offset().

Fixes: 9ffc7a635c35a ("selftests/seccomp: validate uprobe syscall passes through seccomp")
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 874f17763536..2584f4f5c062 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -5172,7 +5172,8 @@ FIXTURE_SETUP(UPROBE)
 		ASSERT_GE(bit, 0);
 	}
 
-	offset = get_uprobe_offset(variant->uretprobe ? probed_uretprobe : probed_uprobe);
+	offset = get_uprobe_offset(variant->uretprobe ?
+				   (void *)probed_uretprobe : (void *)probed_uprobe);
 	ASSERT_GE(offset, 0);
 
 	if (variant->uretprobe)
-- 
2.43.0

[PATCH 10/13] selftests: net: Work around build error seen with -Werror

[Guenter Roeck]

Fix

ksft.h: In function ‘ksft_ready’:
ksft.h:27:9: error: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’

ksft.h: In function ‘ksft_wait’:
ksft.h:51:9: error: ignoring return value of ‘read’ declared with attribute ‘warn_unused_result’

by checking and then ignoring the return value of the affected functions.

Fixes: 2b6d490b82668 ("selftests: drv-net: Factor out ksft C helpers")
Cc: Joe Damato <jdamato@fastly.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/net/lib/ksft.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/lib/ksft.h b/tools/testing/selftests/net/lib/ksft.h
index 17dc34a612c6..b3d3f7e28e98 100644
--- a/tools/testing/selftests/net/lib/ksft.h
+++ b/tools/testing/selftests/net/lib/ksft.h
@@ -24,7 +24,8 @@ static inline void ksft_ready(void)
 		fd = STDOUT_FILENO;
 	}
 
-	write(fd, msg, sizeof(msg));
+	if (write(fd, msg, sizeof(msg)))
+		;
 	if (fd != STDOUT_FILENO)
 		close(fd);
 }
@@ -48,7 +49,8 @@ static inline void ksft_wait(void)
 		fd = STDIN_FILENO;
 	}
 
-	read(fd, &byte, sizeof(byte));
+	if (read(fd, &byte, sizeof(byte)))
+		;
 	if (fd != STDIN_FILENO)
 		close(fd);
 }
-- 
2.43.0

[PATCH 11/13] selftests/fs/mount-notify: Fix build failure seen with -Werror

[Guenter Roeck]

Fix

mount-notify_test.c: In function ‘fanotify_rmdir’:
mount-notify_test.c:467:17: error:
	ignoring return value of ‘chdir’ declared with attribute ‘warn_unused_result’

by checking and then ignoring the return value of chdir().

Fixes: e1c24b52adb22 ("selftests: add tests for mount notification")
Cc: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 .../selftests/filesystems/mount-notify/mount-notify_test.c     | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/filesystems/mount-notify/mount-notify_test.c b/tools/testing/selftests/filesystems/mount-notify/mount-notify_test.c
index e4b7c2b457ee..c53383d4167c 100644
--- a/tools/testing/selftests/filesystems/mount-notify/mount-notify_test.c
+++ b/tools/testing/selftests/filesystems/mount-notify/mount-notify_test.c
@@ -464,7 +464,8 @@ TEST_F(fanotify, rmdir)
 	ASSERT_GE(ret, 0);
 
 	if (ret == 0) {
-		chdir("/");
+		if (chdir("/"))
+			;
 		unshare(CLONE_NEWNS);
 		mount("", "/", NULL, MS_REC|MS_PRIVATE, NULL);
 		umount2("/a", MNT_DETACH);
-- 
2.43.0

[PATCH 12/13] selftests/fs/mount-notify-ns: Fix build failures seen with -Werror

[Guenter Roeck]

Fix

mount-notify_test_ns.c: In function ‘fanotify_rmdir’:
mount-notify_test_ns.c:494:17: error:
	ignoring return value of ‘chdir’ declared with attribute ‘warn_unused_result’

by checking and then ignoring the return value of chdir().

Fixes: 781091f3f5945 ("selftests/fs/mount-notify: add a test variant running inside userns")
Cc: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 .../selftests/filesystems/mount-notify/mount-notify_test_ns.c  | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/filesystems/mount-notify/mount-notify_test_ns.c b/tools/testing/selftests/filesystems/mount-notify/mount-notify_test_ns.c
index 9f57ca46e3af..949c76797f92 100644
--- a/tools/testing/selftests/filesystems/mount-notify/mount-notify_test_ns.c
+++ b/tools/testing/selftests/filesystems/mount-notify/mount-notify_test_ns.c
@@ -491,7 +491,8 @@ TEST_F(fanotify, rmdir)
 	ASSERT_GE(ret, 0);
 
 	if (ret == 0) {
-		chdir("/");
+		if (chdir("/"))
+			;
 		unshare(CLONE_NEWNS);
 		mount("", "/", NULL, MS_REC|MS_PRIVATE, NULL);
 		umount2("/a", MNT_DETACH);
-- 
2.43.0

[PATCH 13/13] selftests: net: tfo: Fix build error seen with -Werror

[Guenter Roeck]

Fix

tfo.c: In function ‘run_server’:
tfo.c:84:9: error: ignoring return value of ‘read’ declared with attribute ‘warn_unused_result’

by evaluating and then ignoring the return value from the read() call.

Fixes: c65b5bb2329e3 ("selftests: net: add passive TFO test binary")
Cc: David Wei <dw@davidwei.uk>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 tools/testing/selftests/net/tfo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/tfo.c b/tools/testing/selftests/net/tfo.c
index eb3cac5e583c..0126e600a36b 100644
--- a/tools/testing/selftests/net/tfo.c
+++ b/tools/testing/selftests/net/tfo.c
@@ -81,7 +81,8 @@ static void run_server(void)
 	if (getsockopt(connfd, SOL_SOCKET, SO_INCOMING_NAPI_ID, &opt, &len) < 0)
 		error(1, errno, "getsockopt(SO_INCOMING_NAPI_ID)");
 
-	read(connfd, buf, 64);
+	if (read(connfd, buf, 64))
+		;
 	fprintf(outfile, "%d\n", opt);
 
 	fclose(outfile);
-- 
2.43.0

Re: [PATCH 00/13] selftests: Fix problems seen when building with -Werror

[Jakub Kicinski]

On Thu,  4 Dec 2025 08:17:14 -0800 Guenter Roeck wrote:
> This series fixes build errors observed when trying to build selftests
> with -Werror.

If your intention is to make -Werror the default please stop.
Defaulting WERROR to enabled is one of the silliest things we have done
in recent past.

People will try to use new compilers on a kernel after it has already
been released. Not being able to build the kernel because of some false
positive warning in another subsystem is so annoying :|

Re: [PATCH 10/13] selftests: net: Work around build error seen with -Werror

[Jakub Kicinski]

On Thu,  4 Dec 2025 08:17:24 -0800 Guenter Roeck wrote:
> -	write(fd, msg, sizeof(msg));
> +	if (write(fd, msg, sizeof(msg)))
> +		;

At least add an perror here ?

Re: [PATCH 00/13] selftests: Fix problems seen when building with -Werror

[Guenter Roeck]

On Thu, Dec 04, 2025 at 08:27:54AM -0800, Jakub Kicinski wrote:
> On Thu,  4 Dec 2025 08:17:14 -0800 Guenter Roeck wrote:
> > This series fixes build errors observed when trying to build selftests
> > with -Werror.
> 
> If your intention is to make -Werror the default please stop.
> Defaulting WERROR to enabled is one of the silliest things we have done
> in recent past.
> 

No, that is not the idea, and not the intention.

The Google infrastructure builds the kernel, including selftests, with
-Werror enabled. This triggers a number of build errors when trying to
build selftests with the 6.18 kernel. That means I have three options:
1) Disable -Werror in selftest builds and accept that some real problems
   will slip through. Not really a good option, and not acceptable.
2) Fix the problems in the upstream kernel and backport.
3) Fix the problems downstream only. Not really a good option but I guess
   we'll have to do it if this series (and/or follow-up patches needed to
   support glibc older than 2.36) is rejected.

We'll have to carry the patches downstream if 2) is rejected, but at
the very least I wanted to give it a try.

Guenter

Re: [PATCH 10/13] selftests: net: Work around build error seen with -Werror

[Guenter Roeck]

On Thu, Dec 04, 2025 at 08:30:29AM -0800, Jakub Kicinski wrote:
> On Thu,  4 Dec 2025 08:17:24 -0800 Guenter Roeck wrote:
> > -	write(fd, msg, sizeof(msg));
> > +	if (write(fd, msg, sizeof(msg)))
> > +		;
> 
> At least add an perror here ?

Makes sense. I'll do that in all patches unless someone has a better idea.

Thanks,
Guenter

Re: [PATCH 06/13] selftest: af_unix: Support compilers without flex-array-member-not-at-end support

[Jakub Kicinski]

On Thu,  4 Dec 2025 08:17:20 -0800 Guenter Roeck wrote:
> -CFLAGS += $(KHDR_INCLUDES) -Wall -Wflex-array-member-not-at-end
> +CFLAGS += $(KHDR_INCLUDES) -Wall $(call cc-option,-Wflex-array-member-not-at-end)

Hm, the Claude code review we have hooked up to patchwork says:

  Is cc-option available in the selftest build environment? Looking at
  tools/testing/selftests/lib.mk (included at line 14), it doesn't include
  scripts/Makefile.compiler where cc-option is defined. When cc-option is
  undefined, $(call cc-option,...) expands to an empty string, which means
  the -Wflex-array-member-not-at-end flag won't be added even on compilers
  that support it.

  This defeats the purpose of commit 1838731f1072c which added the warning
  flag to catch flexible array issues.

  For comparison, tools/testing/selftests/nolibc/Makefile explicitly
  includes scripts/Makefile.compiler before using cc-option.

Testing it:

$ make -C tools/testing/selftests/ TARGETS=net/af_unix Q= V=1
make: Entering directory '/home/kicinski/devel/linux/tools/testing/selftests'
make[1]: Entering directory '/home/kicinski/devel/linux/tools/testing/selftests/net/af_unix'
gcc -isystem /home/kicinski/devel/linux/usr/include -Wall  -D_GNU_SOURCE=     diag_uid.c  -o /home/kicinski/devel/linux/tools/testing/selftests/net/af_unix/diag_uid

looks like the flag just disappears. Even tho:

gcc version 15.2.1 

Re: [PATCH 00/13] selftests: Fix problems seen when building with -Werror

[Jakub Kicinski]

On Thu, 4 Dec 2025 09:16:16 -0800 Guenter Roeck wrote:
> On Thu, Dec 04, 2025 at 08:27:54AM -0800, Jakub Kicinski wrote:
> > On Thu,  4 Dec 2025 08:17:14 -0800 Guenter Roeck wrote:  
> > > This series fixes build errors observed when trying to build selftests
> > > with -Werror.  
> > 
> > If your intention is to make -Werror the default please stop.
> > Defaulting WERROR to enabled is one of the silliest things we have done
> > in recent past.
> 
> No, that is not the idea, and not the intention.
> 
> The Google infrastructure builds the kernel, including selftests, with
> -Werror enabled. This triggers a number of build errors when trying to
> build selftests with the 6.18 kernel. That means I have three options:
> 1) Disable -Werror in selftest builds and accept that some real problems
>    will slip through. Not really a good option, and not acceptable.
> 2) Fix the problems in the upstream kernel and backport.
> 3) Fix the problems downstream only. Not really a good option but I guess
>    we'll have to do it if this series (and/or follow-up patches needed to
>    support glibc older than 2.36) is rejected.
> 
> We'll have to carry the patches downstream if 2) is rejected, but at
> the very least I wanted to give it a try.

Understood, of course we should fix the warnings!
If we're fixing warnings, tho, I wouldn't have mentioned -Werror in 
the _subject_. It doesn't affect which warnings are enabled, AFAIK?

Re: [PATCH 00/13] selftests: Fix problems seen when building with -Werror

[Guenter Roeck]

On Thu, Dec 04, 2025 at 09:43:20AM -0800, Jakub Kicinski wrote:
> On Thu, 4 Dec 2025 09:16:16 -0800 Guenter Roeck wrote:
> > On Thu, Dec 04, 2025 at 08:27:54AM -0800, Jakub Kicinski wrote:
> > > On Thu,  4 Dec 2025 08:17:14 -0800 Guenter Roeck wrote:  
> > > > This series fixes build errors observed when trying to build selftests
> > > > with -Werror.  
> > > 
> > > If your intention is to make -Werror the default please stop.
> > > Defaulting WERROR to enabled is one of the silliest things we have done
> > > in recent past.
> > 
> > No, that is not the idea, and not the intention.
> > 
> > The Google infrastructure builds the kernel, including selftests, with
> > -Werror enabled. This triggers a number of build errors when trying to
> > build selftests with the 6.18 kernel. That means I have three options:
> > 1) Disable -Werror in selftest builds and accept that some real problems
> >    will slip through. Not really a good option, and not acceptable.
> > 2) Fix the problems in the upstream kernel and backport.
> > 3) Fix the problems downstream only. Not really a good option but I guess
> >    we'll have to do it if this series (and/or follow-up patches needed to
> >    support glibc older than 2.36) is rejected.
> > 
> > We'll have to carry the patches downstream if 2) is rejected, but at
> > the very least I wanted to give it a try.
> 
> Understood, of course we should fix the warnings!
> If we're fixing warnings, tho, I wouldn't have mentioned -Werror in 
> the _subject_. It doesn't affect which warnings are enabled, AFAIK?

I'll update the subjects and descriptions accordingly.

Thanks,
Guenter

Re: [PATCH 06/13] selftest: af_unix: Support compilers without flex-array-member-not-at-end support

[Guenter Roeck]

On Thu, Dec 04, 2025 at 09:40:54AM -0800, Jakub Kicinski wrote:
> On Thu,  4 Dec 2025 08:17:20 -0800 Guenter Roeck wrote:
> > -CFLAGS += $(KHDR_INCLUDES) -Wall -Wflex-array-member-not-at-end
> > +CFLAGS += $(KHDR_INCLUDES) -Wall $(call cc-option,-Wflex-array-member-not-at-end)
> 
> Hm, the Claude code review we have hooked up to patchwork says:
> 
>   Is cc-option available in the selftest build environment? Looking at
>   tools/testing/selftests/lib.mk (included at line 14), it doesn't include
>   scripts/Makefile.compiler where cc-option is defined. When cc-option is
>   undefined, $(call cc-option,...) expands to an empty string, which means
>   the -Wflex-array-member-not-at-end flag won't be added even on compilers
>   that support it.
> 
>   This defeats the purpose of commit 1838731f1072c which added the warning
>   flag to catch flexible array issues.
> 
>   For comparison, tools/testing/selftests/nolibc/Makefile explicitly
>   includes scripts/Makefile.compiler before using cc-option.
> 
> Testing it:
> 
> $ make -C tools/testing/selftests/ TARGETS=net/af_unix Q= V=1
> make: Entering directory '/home/kicinski/devel/linux/tools/testing/selftests'
> make[1]: Entering directory '/home/kicinski/devel/linux/tools/testing/selftests/net/af_unix'
> gcc -isystem /home/kicinski/devel/linux/usr/include -Wall  -D_GNU_SOURCE=     diag_uid.c  -o /home/kicinski/devel/linux/tools/testing/selftests/net/af_unix/diag_uid
> 
> looks like the flag just disappears. Even tho:
> 
> gcc version 15.2.1 

Oops :). I didn't expect that, sorry. Thanks for finding!

... and I guess it's time to set up AI in my environment.

Guenter

Re: [PATCH 00/13] selftests: Fix problems seen when building with -Werror

[Kees Cook]

On Thu, Dec 04, 2025 at 09:16:16AM -0800, Guenter Roeck wrote:
> On Thu, Dec 04, 2025 at 08:27:54AM -0800, Jakub Kicinski wrote:
> > On Thu,  4 Dec 2025 08:17:14 -0800 Guenter Roeck wrote:
> > > This series fixes build errors observed when trying to build selftests
> > > with -Werror.
> > 
> > If your intention is to make -Werror the default please stop.
> > Defaulting WERROR to enabled is one of the silliest things we have done
> > in recent past.
> > 
> 
> No, that is not the idea, and not the intention.
> 
> The Google infrastructure builds the kernel, including selftests, with
> -Werror enabled. This triggers a number of build errors when trying to
> build selftests with the 6.18 kernel. That means I have three options:
> 1) Disable -Werror in selftest builds and accept that some real problems
>    will slip through. Not really a good option, and not acceptable.
> 2) Fix the problems in the upstream kernel and backport.

The series fixes build warnings that appear regardless of -Werror,
yes? That on its face is an improvement, so maybe just adjust the
Subject/changelogs?

-- 
Kees Cook

Re: [PATCH 00/13] selftests: Fix problems seen when building with -Werror

[Guenter Roeck]

On Thu, Dec 04, 2025 at 12:03:29PM -0800, Kees Cook wrote:
> On Thu, Dec 04, 2025 at 09:16:16AM -0800, Guenter Roeck wrote:
> > On Thu, Dec 04, 2025 at 08:27:54AM -0800, Jakub Kicinski wrote:
> > > On Thu,  4 Dec 2025 08:17:14 -0800 Guenter Roeck wrote:
> > > > This series fixes build errors observed when trying to build selftests
> > > > with -Werror.
> > > 
> > > If your intention is to make -Werror the default please stop.
> > > Defaulting WERROR to enabled is one of the silliest things we have done
> > > in recent past.
> > > 
> > 
> > No, that is not the idea, and not the intention.
> > 
> > The Google infrastructure builds the kernel, including selftests, with
> > -Werror enabled. This triggers a number of build errors when trying to
> > build selftests with the 6.18 kernel. That means I have three options:
> > 1) Disable -Werror in selftest builds and accept that some real problems
> >    will slip through. Not really a good option, and not acceptable.
> > 2) Fix the problems in the upstream kernel and backport.
> 
> The series fixes build warnings that appear regardless of -Werror,
> yes? That on its face is an improvement, so maybe just adjust the
> Subject/changelogs?
> 
Yes, I'll do that.

Thanks,
Guenter