Messages in this thread Patch in this message | | | From | Cao jin <> | Subject | [PATCH] x86/cpufeature: explicit comments for duplicate macro | Date | Wed, 28 Aug 2019 14:11:00 +0800 |
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Help people to understand the author's intent of apparent duplication of BUILD_BUG_ON_ZERO(NCAPINTS != n), which is hard to detect by eyes.
CC: Dave Hansen <dave.hansen@intel.com> Suggested-by: Borislav Petkov <bp@alien8.de> Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com> --- Tried my best to describe it accurately, in case of any inaccuracy, feel free to rephrase.
arch/x86/include/asm/cpufeature.h | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 58acda503817..e943174abf1e 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -61,6 +61,17 @@ extern const char * const x86_bug_flags[NBUGINTS*32]; #define CHECK_BIT_IN_MASK_WORD(maskname, word, bit) \ (((bit)>>5)==(word) && (1UL<<((bit)&31) & maskname##word )) +/* + * REQUIRED_MASK_CHECK may seems duplicate, but actually has its reason to + * live here. + * New CPUID leaf added or feature bit adjustment would/may result in increase + * in NCAPINTS. When it does, two required-features.h and here need to be + * modified correspondingly. BUILD_BUG_ON_ZERO assures the modification to be + * carried out, checking NCAPINTS also reminds the additional lines for new + * word. But, required-features.h as a single header file, can't be compiled + * directly, that is why a wrapper is defined there and called here. + * Totally the same case for DISABLED_MASK_BIT_SET. + */ #define REQUIRED_MASK_BIT_SET(feature_bit) \ ( CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 0, feature_bit) || \ CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 1, feature_bit) || \ -- 2.17.0
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