[patch 0/2] x86/vdso: Address sparse warnings

[patch 0/2] x86/vdso: Address sparse warnings

[Thomas Gleixner]

Sparse is unhappy when building the 32-bit VDSO for a 64-bit kernel and
complains about an empty switch statement when all config knobs which guard
the cases are disabled.

The following series cures both.

Thanks,

	tglx
---
 Makefile |    4 ++++
 vma.c    |    2 ++
 2 files changed, 6 insertions(+)

[patch 1/2] x86/vdso: Tweak CHECKFLAGS for 32-bit VDSO build

[Thomas Gleixner]

Sparse complains about a too large shift in the VDSO32 source file:

  arch/x86/entry/vdso/vdso32/vclock_gettime.c: note: in included file (through /home/tglx/work/kernel/tip/tip/arch/x86/entry/vdso/vdso32/../vclock_gettime.c):
  arch/x86/entry/vdso/vdso32/../../../../../lib/vdso/gettimeofday.c:454:26: warning: shift too big (40) for type unsigned long

That's because sparse is invoked with -D__x86_64__ -m64 on the command
line, which causes it to use __BITS_PER_LONG = 64. That causes __GENMASK()
to use a way too big shift value.

Give the CHECKFLAGS which are handed to sparse a similar treatment as
KBUILD_CFLAGS get for the 32-bit VDSO build.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
---
 arch/x86/entry/vdso/Makefile |    4 ++++
 1 file changed, 4 insertions(+)

--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -144,6 +144,10 @@ endif
 
 $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)
 
+CHECKFLAGS_32 := $(subst -m64,-m32,$(CHECKFLAGS))
+CHECKFLAGS_32 := $(subst -D__x86_64__,-D__i386__,$(CHECKFLAGS_32))
+$(obj)/vdso32.so.dbg: CHECKFLAGS = $(CHECKFLAGS_32)
+
 $(obj)/vdso32.so.dbg: $(obj)/vdso32/vdso32.lds $(vobjs32) FORCE
 	$(call if_changed,vdso_and_check)
 

[patch 2/2] x86/vdso: Prevent empty switch case warning

[Thomas Gleixner]

Sparse complains rightfully when CONFIG_PARAVIRT_CLOCK and
CONFIG_HYPERV_TIMER are both not set:

  arch/x86/entry/vdso/vma.c:94:9: warning: switch with no cases

Add a default case to fix that.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
---
 arch/x86/entry/vdso/vma.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -114,6 +114,8 @@ static vm_fault_t vvar_vclock_fault(cons
 		break;
 	}
 #endif /* CONFIG_HYPERV_TIMER */
+	default:
+		break;
 	}
 
 	return VM_FAULT_SIGBUS;

Re: [patch 2/2] x86/vdso: Prevent empty switch case warning

[Thomas Weißschuh]

Hi,

On Sat, Jan 17, 2026 at 10:58:27PM +0100, Thomas Gleixner wrote:
> Sparse complains rightfully when CONFIG_PARAVIRT_CLOCK and
> CONFIG_HYPERV_TIMER are both not set:
> 
>   arch/x86/entry/vdso/vma.c:94:9: warning: switch with no cases
> 
> Add a default case to fix that.
> 
> Signed-off-by: Thomas Gleixner <tglx@kernel.org>
> ---
>  arch/x86/entry/vdso/vma.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -114,6 +114,8 @@ static vm_fault_t vvar_vclock_fault(cons
>  		break;
>  	}
>  #endif /* CONFIG_HYPERV_TIMER */
> +	default:
> +		break;

This makes the code uglier only to pacify sparse.
It turns out all the necessary stub functions are in place to just
delete the ifdefs altogether. Maybe replace them with IS_ENABLED()
to make it clearer to reader what is going on.

>  	}
>  
>  	return VM_FAULT_SIGBUS;
> 

Re: [patch 1/2] x86/vdso: Tweak CHECKFLAGS for 32-bit VDSO build

[Thomas Weißschuh]

On Sat, Jan 17, 2026 at 10:58:25PM +0100, Thomas Gleixner wrote:
> Sparse complains about a too large shift in the VDSO32 source file:
> 
>   arch/x86/entry/vdso/vdso32/vclock_gettime.c: note: in included file (through /home/tglx/work/kernel/tip/tip/arch/x86/entry/vdso/vdso32/../vclock_gettime.c):
>   arch/x86/entry/vdso/vdso32/../../../../../lib/vdso/gettimeofday.c:454:26: warning: shift too big (40) for type unsigned long
> 
> That's because sparse is invoked with -D__x86_64__ -m64 on the command
> line, which causes it to use __BITS_PER_LONG = 64. That causes __GENMASK()
> to use a way too big shift value.
> 
> Give the CHECKFLAGS which are handed to sparse a similar treatment as
> KBUILD_CFLAGS get for the 32-bit VDSO build.
> 
> Signed-off-by: Thomas Gleixner <tglx@kernel.org>

Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

> ---
>  arch/x86/entry/vdso/Makefile |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -144,6 +144,10 @@ endif
>  
>  $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)
>  
> +CHECKFLAGS_32 := $(subst -m64,-m32,$(CHECKFLAGS))
> +CHECKFLAGS_32 := $(subst -D__x86_64__,-D__i386__,$(CHECKFLAGS_32))
> +$(obj)/vdso32.so.dbg: CHECKFLAGS = $(CHECKFLAGS_32)

It would be nice if we had a strict variant of $(subst ...) which errors
out if nothing is substituted.

> +
>  $(obj)/vdso32.so.dbg: $(obj)/vdso32/vdso32.lds $(vobjs32) FORCE
>  	$(call if_changed,vdso_and_check)
>  
> 

Re: [patch 1/2] x86/vdso: Tweak CHECKFLAGS for 32-bit VDSO build

[Thomas Gleixner]

On Mon, Jan 19 2026 at 08:18, Thomas Weißschuh wrote:
> On Sat, Jan 17, 2026 at 10:58:25PM +0100, Thomas Gleixner wrote:
>>  $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)
>>  
>> +CHECKFLAGS_32 := $(subst -m64,-m32,$(CHECKFLAGS))
>> +CHECKFLAGS_32 := $(subst -D__x86_64__,-D__i386__,$(CHECKFLAGS_32))
>> +$(obj)/vdso32.so.dbg: CHECKFLAGS = $(CHECKFLAGS_32)
>
> It would be nice if we had a strict variant of $(subst ...) which errors
> out if nothing is substituted.

Which would fail a arch=i386 build then, no? :)