Commit cbb1133b authored Aug 28, 2019 by Cao Jin Committed by Borislav Petkov Aug 28, 2019

x86/cpufeature: Explain the macro duplication



Explain the intent behind the duplication of the

  BUILD_BUG_ON_ZERO(NCAPINTS != n)

check in *_MASK_CHECK and its immediate use in the *MASK_BIT_SET macros
too.

 [ bp: Massage. ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Cao Jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nadav Amit <namit@vmware.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190828061100.27032-1-caoj.fnst@cn.fujitsu.com

parent 248d327e

arch/x86/include/asm/cpufeature.h

+7 −0

Original line number	Diff line number	Diff line
		@@ -61,6 +61,13 @@ 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,DISABLED}_MASK_CHECK below may seem duplicated with the
		* following BUILD_BUG_ON_ZERO() check but when NCAPINTS gets changed, all
		* header macros which use NCAPINTS need to be changed. The duplicated macro
		* use causes the compiler to issue errors for all headers so that all usage
		* sites can be corrected.
		*/
		#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) \|\| \