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 <[email protected]>
Suggested-by: Borislav Petkov <[email protected]>
Signed-off-by: Cao jin <[email protected]>
---
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
On Wed, Aug 28, 2019 at 02:11:00PM +0800, Cao jin wrote:
For the future:
> Subject: Re: [PATCH] x86/cpufeature: explicit comments for duplicate macro
your subject needs to have a verb and start with a capital letter after
the subsystem/path prefix. In this case, something like this, for
example:
Subject: [PATCH] x86/cpufeature: Explain the macro duplication
> 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 <[email protected]>
> Suggested-by: Borislav Petkov <[email protected]>
> Signed-off-by: Cao jin <[email protected]>
> ---
> Tried my best to describe it accurately, in case of any inaccuracy, feel
> free to rephrase.
Yap, I fixed it up.
Thanks!
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
The following commit has been merged into the x86/cleanups branch of tip:
Commit-ID: cbb1133b563a63901cf778220eb17e3ff1425aed
Gitweb: https://git.kernel.org/tip/cbb1133b563a63901cf778220eb17e3ff1425aed
Author: Cao Jin <[email protected]>
AuthorDate: Wed, 28 Aug 2019 14:11:00 +08:00
Committer: Borislav Petkov <[email protected]>
CommitterDate: Wed, 28 Aug 2019 08:38:39 +02:00
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 <[email protected]>
Signed-off-by: Cao Jin <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
arch/x86/include/asm/cpufeature.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 58acda5..59bf91c 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -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) || \
On 8/28/19 2:42 PM, Borislav Petkov wrote:
> On Wed, Aug 28, 2019 at 02:11:00PM +0800, Cao jin wrote:
>
> For the future:
>
>> Subject: Re: [PATCH] x86/cpufeature: explicit comments for duplicate macro
>
> your subject needs to have a verb and start with a capital letter after
> the subsystem/path prefix. In this case, something like this, for
> example:
>
> Subject: [PATCH] x86/cpufeature: Explain the macro duplication
>
Kept that in mind. Thanks very much!
--
Sincerely,
Cao jin