[PATCH] x86/init: Initialize wall clock in get_rtc_noop()

[PATCH] x86/init: Initialize wall clock in get_rtc_noop()

[Naman Jain]

get_rtc_noop() is used when an RTC is unavailable, but leaves its output
argument untouched. When CONFIG_INIT_STACK_ALL_ZERO is not enabled,
timekeeping_init() may therefore receive a nonzero invalid persistent
clock value and warn:
"Persistent clock returned invalid value"

Initialize the output to zero, the documented representation of an
unsupported persistent clock.

Fixes: c311ed6183f4 ("x86/init: Allow DT configured systems to disable RTC at boot time")
Cc: stable@vger.kernel.org
Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
---
 arch/x86/kernel/x86_init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index 252c5827d0634..3b9b41820c84c 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -37,7 +37,7 @@ static void iommu_shutdown_noop(void) { }
 bool __init bool_x86_init_noop(void) { return false; }
 void x86_op_int_noop(int cpu) { }
 int set_rtc_noop(const struct timespec64 *now) { return -EINVAL; }
-void get_rtc_noop(struct timespec64 *now) { }
+void get_rtc_noop(struct timespec64 *now) { *now = (struct timespec64){0}; }
 
 static __initconst const struct of_device_id of_cmos_match[] = {
 	{ .compatible = "motorola,mc146818" },
-- 
2.43.0

RE: [PATCH] x86/init: Initialize wall clock in get_rtc_noop()

[Dexuan Cui]

> From: Naman Jain <namjain@linux.microsoft.com>
> Sent: Monday, August 31, 2026 1:25 AM

LGTM.

Reviewed-by: Dexuan Cui <decui@microsoft.com>

Re: [PATCH] x86/init: Initialize wall clock in get_rtc_noop()

[Hardik Garg]

Reviewed-by: Hardik Garg <hargar@linux.microsoft.com>

Re: [PATCH] x86/init: Initialize wall clock in get_rtc_noop()

[Roman Kisel]

On Mon, Aug 31, 2026 at 08:25:28AM +0000, Naman Jain wrote:
> get_rtc_noop() is used when an RTC is unavailable, but leaves its output
> argument untouched. When CONFIG_INIT_STACK_ALL_ZERO is not enabled,
> timekeeping_init() may therefore receive a nonzero invalid persistent
> clock value and warn:
> "Persistent clock returned invalid value"
> 
> Initialize the output to zero, the documented representation of an
> unsupported persistent clock.
> 
> Fixes: c311ed6183f4 ("x86/init: Allow DT configured systems to disable RTC at boot time")
> Cc: stable@vger.kernel.org
> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
> ---
>  arch/x86/kernel/x86_init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
> index 252c5827d0634..3b9b41820c84c 100644
> --- a/arch/x86/kernel/x86_init.c
> +++ b/arch/x86/kernel/x86_init.c
> @@ -37,7 +37,7 @@ static void iommu_shutdown_noop(void) { }
>  bool __init bool_x86_init_noop(void) { return false; }
>  void x86_op_int_noop(int cpu) { }
>  int set_rtc_noop(const struct timespec64 *now) { return -EINVAL; }
> -void get_rtc_noop(struct timespec64 *now) { }
> +void get_rtc_noop(struct timespec64 *now) { *now = (struct timespec64){0}; }

Hi Naman,

Could be

*now = (struct timespec64){};

to save a byte :)

LGTM.
Reviewed-by: Roman Kisel <vdso@mailbox.org>

>  
>  static __initconst const struct of_device_id of_cmos_match[] = {
>  	{ .compatible = "motorola,mc146818" },
> -- 
> 2.43.0
>