linux-kernel - Re: [PATCH v2 12/14] selftests: vDSO: vdso_test_correctness: Use system call wrappers from vdso

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Message-Id: <c3a23032-5e25-429b-b096-e9bc0a72d026@app.fastmail.com>
Date: Fri, 14 Nov 2025 09:01:13 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 "Andy Lutomirski" <luto@...nel.org>, "Thomas Gleixner" <tglx@...utronix.de>,
 "Vincenzo Frascino" <vincenzo.frascino@....com>, shuah <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 12/14] selftests: vDSO: vdso_test_correctness: Use system call
 wrappers from vdso_syscalls.h

On Thu, Nov 13, 2025, at 16:30, Thomas Weißschuh wrote:

> 
>  static void test_one_clock_gettime(int clock, const char *name)
>  {
> +	struct __kernel_timespec start, end;
>  	struct __kernel_old_timespec vdso;
> -	struct timespec start, end;
>  	int vdso_ret, end_ret;
> 
>  	printf("[RUN]\tTesting clock_gettime for clock %s (%d)...\n", name, 

This looks confusing to me: I can see that the existing code is
wrong because it passes a (libc-defined) timespec into the
sys_clock_gettime() that expects __kernel_old_timespec.

It looks like you are changing a sometimes-wrong type into
a consistently wrong type, but then you also change the
sys_clock_gettime() definition to return __kernel_timespec
instead of __kernel_old_timespec, so it ends up working.

Why not always use __kernel_old_timespec for the local variables
and the sys_clock_gettime() calls here?

> @@ -305,7 +291,7 @@ static void test_one_clock_gettime64(int clock, const char *name)
> 
> 	printf("[RUN]\tTesting clock_gettime64 for clock %s (%d)...\n", name, clock);
> 
> -	if (sys_clock_gettime64(clock, &start) < 0) {
> +	if (sys_clock_gettime(clock, &start) < 0) {
> 		if (errno == EINVAL) {
>  			vdso_ret = VDSO_CALL(vdso_clock_gettime64, 2, clock, &vdso);
> 			if (vdso_ret == -EINVAL) {

This looks like the correct fix to me. We were already uses the same
types for syscall and vdso paths, and now the types match the interface.

     Arnd