Re: [PATCH] um: Use asm-generic/timex.h over the host architecture one

[SJ Park <sj@kernel.org>]

On Wed, 19 Aug 2026 09:24:21 +0200 Thomas Weißschuh <thomas.weissschuh@linutronix.de> wrote:

> The removal of the architecture-specific asm/timex.h was meant to fall
> back to asm-generic/timex.h. However on UML, the host architecture
> headers are earlier on the include path and therefore asm/timex.h from
> the host architecture is used.
> On x86 that header in turn requires the generation of cpufeaturemasks.h,
> which is not set up for UML and the build fails.
> 
> In file included from ../arch/x86/include/asm/tsc.h:9,
>                  from ../arch/x86/include/asm/timex.h:6,
>                  from ../include/linux/timex.h:67,
>                  from ../include/linux/time32.h:13,
>                  from ../include/linux/time.h:60,
>                  from ../include/linux/jiffies.h:10,
>                  from ../include/linux/ktime.h:25,
>                  from ../include/linux/timer.h:6,
>                  from ../include/linux/uprobes.h:18,
>                  from ../include/linux/mm_types.h:16,
>                  from ../include/linux/mmzone.h:22,
>                  from ../include/linux/gfp.h:7,
>                  from ../include/linux/slab.h:17,
>                  from ../include/linux/crypto.h:18,
>                  from ../arch/um/kernel/asm-offsets.c:6:
> arch/x86/include/asm/tsc.h: In function ‘get_cycles’:
> arch/um/include/asm/cpufeature.h:52:39: error: implicit declaration of function ‘DISABLED_MASK_BIT_SET’ [-Wimplicit-function-declaration]
>    52 |         (__builtin_constant_p(bit) && DISABLED_MASK_BIT_SET(bit) ? 0 : _static_cpu_has(bit))
>       |                                       ^~~~~~~~~~~~~~~~~~~~~
> arch/x86/include/asm/tsc.h:79:14: note: in expansion of macro ‘cpu_feature_enabled’
>    79 |         if (!cpu_feature_enabled(X86_FEATURE_TSC))
>       |              ^~~~~~~~~~~~~~~~~~~
> arch/um/include/asm/cpufeature.h:115:17: error: implicit declaration of function ‘_static_cpu_has’ [-Wimplicit-function-declaration]
>   115 |                 _static_cpu_has(bit)                            \
>       |                 ^~~~~~~~~~~~~~~
> arch/um/include/asm/cpufeature.h:52:72: note: in expansion of macro ‘_static_cpu_has’
>    52 |         (__builtin_constant_p(bit) && DISABLED_MASK_BIT_SET(bit) ? 0 : _static_cpu_has(bit))
>       |                                                                        ^~~~~~~~~~~~~~~
> arch/x86/include/asm/tsc.h:79:14: note: in expansion of macro ‘cpu_feature_enabled’
>    79 |         if (!cpu_feature_enabled(X86_FEATURE_TSC))
>       |              ^~~~~~~~~~~~~~~~~~~
> arch/um/include/asm/cpufeature.h:115:17: note: ‘_static_cpu_has’ is a function-like macro and might be used incorrectly
> arch/um/include/asm/cpufeature.h:52:72: note: in expansion of macro ‘_static_cpu_has’
>    52 |         (__builtin_constant_p(bit) && DISABLED_MASK_BIT_SET(bit) ? 0 : _static_cpu_has(bit))
>       |                                                                        ^~~~~~~~~~~~~~~
> arch/x86/include/asm/tsc.h:79:14: note: in expansion of macro ‘cpu_feature_enabled’
>    79 |         if (!cpu_feature_enabled(X86_FEATURE_TSC))
>       |              ^~~~~~~~~~~~~~~~~~~
> 
> The x86-specific timex.h also doesn't make sense on UML in general.
> 
> Reintroduce the UML-specific asm/timex.h and add a comment to document
> its necessity.

I got the same issue, and confirmed this patch fixes it on my setup.  Thank you
for sharing this patch.

> 
> Fixes: 3ed403bbc967 ("treewide: Remove CLOCK_TICK_RATE")
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

Tested-by: SJ Park <sj@kernel.org>


Thanks,
SJ

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