On 8/23/26 22:14, Fabian Franz wrote:
> Since commit 3ed403bbc967 ("treewide: Remove CLOCK_TICK_RATE") deleted
> the (otherwise empty) arch/um/include/asm/timex.h, UML builds resolve
> <asm/timex.h> to arch/x86/include/asm/timex.h via the HEADER_ARCH
> include path. That pulls <asm/tsc.h>, whose get_cycles() uses
> cpu_feature_enabled(), into virtually every translation unit, starting
> with asm-offsets.c. This newly expands parts of UML's copy of
> <asm/cpufeature.h> that no longer compile, and "make ARCH=um" now dies
> in prepare0:
>
> arch/um/include/asm/cpufeature.h:52:39: error: implicit declaration
> of function 'DISABLED_MASK_BIT_SET'
> arch/um/include/asm/cpufeature.h:115:17: error: implicit declaration
> of function '_static_cpu_has'; did you mean '__static_cpu_has'?
To ensure everyone is aware of it: Thomas Weißschuh (now CCed) a few
days ago already submitted a fix for a problem that to my untrained eyes
looks like the same problem (do not hesitate to correct me!):
https://lore.kernel.org/all/[email protected]/
Ciao, Thorsten
> Two independent breakages meet here:
>
> 1. cpu_feature_enabled() and this_cpu_has() still test
> DISABLED_MASK_BIT_SET()/REQUIRED_MASK_BIT_SET(). Those used to
> come from <asm/disabled-features.h>/<asm/required-features.h> via
> <asm/cpufeatures.h>, but since commit 8f97566c8a81
> ("x86/cpufeatures: Remove {disabled,required}-features.h") they
> live in the generated <asm/cpufeaturemasks.h>, which only the
> arch/x86 archprepare rule generates. ARCH=um never generates nor
> includes it, so the references have been dangling since then.
>
> 2. The _static_cpu_has() macro expands to itself. Commit
> 3eaa50e1e255 ("x86/cpu: Hide and rename static_cpu_has()") renamed
> the inline function _static_cpu_has() -> __static_cpu_has() and
> the macro static_cpu_has() -> _static_cpu_has(), but in the UML
> header the macro's out-of-line branch kept calling
> _static_cpu_has(), which now names the macro itself and is left
> unexpanded by the preprocessor.
>
> Fix the macro to call __static_cpu_has(), as the x86 header does, and
> drop the mask based short-circuits from cpu_feature_enabled() and
> this_cpu_has(). UML has no compile-time feature masking to express:
> capabilities are copied from the host's CPUID at boot, see commit
> d8fb32f4790f ("um: Add support for host CPU flags and alignment"),
> and generating cpufeaturemasks.h from a UML .config would wrongly
> mark features disabled simply because the gating CONFIG_X86_* symbols
> do not exist for ARCH=um.
>
> Fixes: 3eaa50e1e255 ("x86/cpu: Hide and rename static_cpu_has()")
> Fixes: 8f97566c8a81 ("x86/cpufeatures: Remove {disabled,required}-features.h")
> Signed-off-by: Fabian Franz <[email protected]>
> Assisted-By: Claude Fable 5 <[email protected]>
> ---
> arch/um/include/asm/cpufeature.h | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/arch/um/include/asm/cpufeature.h
> b/arch/um/include/asm/cpufeature.h
> index f7770083c0a4..20b2c7ead62e 100644
> --- a/arch/um/include/asm/cpufeature.h
> +++ b/arch/um/include/asm/cpufeature.h
> @@ -37,8 +37,7 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
> test_cpu_cap(c, bit)
>
> #define this_cpu_has(bit) \
> - (__builtin_constant_p(bit) && REQUIRED_MASK_BIT_SET(bit) ? 1 : \
> - x86_this_cpu_test_bit(bit, cpu_info.x86_capability))
> + x86_this_cpu_test_bit(bit, cpu_info.x86_capability)
>
> /*
> * This macro is for detection of features which need kernel
> @@ -48,8 +47,7 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
> * supporting a possible guest feature where host support for it
> * is not relevant.
> */
> -#define cpu_feature_enabled(bit) \
> - (__builtin_constant_p(bit) && DISABLED_MASK_BIT_SET(bit) ? 0 :
> _static_cpu_has(bit))
> +#define cpu_feature_enabled(bit) _static_cpu_has(bit)
>
> #define boot_cpu_has(bit) cpu_has(&boot_cpu_data, bit)
>
> @@ -112,7 +110,7 @@ static __always_inline bool __static_cpu_has(u16 bit)
> ( \
> __builtin_constant_p(boot_cpu_has(bit)) ? \
> boot_cpu_has(bit) : \
> - _static_cpu_has(bit) \
> + __static_cpu_has(bit) \
> )
>
> #define cpu_has_bug(c, bit) cpu_has(c, (bit))
>
> --
> 2.43.0
>
> Every ARCH=um build has failed since the 7.3 merge window.
>
> #regzbot introduced: 3ed403bbc967
>
> Steps to reproduce on master:
>
> make ARCH=um O=/tmp/um-build defconfig
> make ARCH=um O=/tmp/um-build -j$(nproc)
>
> fails with:
>
> /home/ubuntu/projects/linux/arch/x86/include/asm/tsc.h: In function
> ‘get_cycles’:
> /home/ubuntu/projects/linux/arch/um/include/asm/cpufeature.h:52:39: error:
> implicit declaration of function ‘DISABLED_MASK_BIT_SET’
> [-Werror=implicit-function-declaration]
> 52 | (__builtin_constant_p(bit) && DISABLED_MASK_BIT_SET(bit) ? 0
> : _static_cpu_has(bit))
> | ^~~~~~~~~~~~~~~~~~~~~
> /home/ubuntu/projects/linux/arch/x86/include/asm/tsc.h:79:14: note: in
> expansion of macro ‘cpu_feature_enabled’
> 79 | if (!cpu_feature_enabled(X86_FEATURE_TSC))
> | ^~~~~~~~~~~~~~~~~~~
> /home/ubuntu/projects/linux/arch/um/include/asm/cpufeature.h:115:17: error:
> implicit declaration of function ‘_static_cpu_has’; did you mean
> ‘__static_cpu_has’? [-Werror=implicit-function-declaration]
> 115 | _static_cpu_has(bit) \
> | ^~~~~~~~~~~~~~~
> /home/ubuntu/projects/linux/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))
> |
> ^~~~~~~~~~~~~~~
>
> If this is known please disregard. I am also not 100% sure if this is the
> right fix or if it's better to bring back the macros to um.
>
> In any case it would be good for um to build again on the master branch out
> of the box.
>
> Thanks,
> Fabian
