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(Postfix) with ESMTPSA id 723183F703; Tue, 21 Feb 2023 02:37:00 -0800 (PST) Date: Tue, 21 Feb 2023 10:36:53 +0000 From: Mark Rutland To: Lin Yujun Cc: catalin.marinas@arm.com, will@kernel.org, broonie@kernel.org, kristina.martsenko@arm.com, james.morse@arm.com, maz@kernel.org, ardb@kernel.org, samitolvanen@google.com, andreyknvl@gmail.com, masahiroy@kernel.org, joey.gouly@arm.com, anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, wanghai38@huawei.com Subject: Re: [PATCH -next] arm64: Optimize the comparison of unsigned expressions to avoid compiling error Message-ID: References: <20230221012740.2929481-1-linyujun809@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20230221012740.2929481-1-linyujun809@huawei.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230221_023709_591988_9884693C X-CRM114-Status: GOOD ( 21.39 ) X-BeenThere: linux-arm-kernel@lists.infradead.org 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05:37:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37264 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232813AbjBUKhF (ORCPT ); Tue, 21 Feb 2023 05:37:05 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id AFF92252AF for ; Tue, 21 Feb 2023 02:37:03 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D716DFEC; Tue, 21 Feb 2023 02:37:45 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.16.87]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 723183F703; Tue, 21 Feb 2023 02:37:00 -0800 (PST) Date: Tue, 21 Feb 2023 10:36:53 +0000 From: Mark Rutland To: Lin Yujun Cc: catalin.marinas@arm.com, will@kernel.org, broonie@kernel.org, kristina.martsenko@arm.com, james.morse@arm.com, maz@kernel.org, ardb@kernel.org, samitolvanen@google.com, andreyknvl@gmail.com, masahiroy@kernel.org, joey.gouly@arm.com, anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, wanghai38@huawei.com Subject: Re: [PATCH -next] arm64: Optimize the comparison of unsigned expressions to avoid compiling error Message-ID: References: <20230221012740.2929481-1-linyujun809@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230221012740.2929481-1-linyujun809@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 21, 2023 at 09:27:40AM +0800, Lin Yujun wrote: > while compile arch/arm64/include/asm/cpufeature.h with > -Werror=type-limits enabled, errors shown as below: > > ./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_4kb_granule': > ./arch/arm64/include/asm/cpufeature.h:653:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits] > return (val >= ID_AA64MMFR0_TGRAN4_SUPPORTED_MIN) && > ^~ > ./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_64kb_granule': > ./arch/arm64/include/asm/cpufeature.h:666:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits] > return (val >= ID_AA64MMFR0_TGRAN64_SUPPORTED_MIN) && > ^~ When is the `-Werror=type-limits` flag enabled by the build system? We have patterns like this all over the kernel, and I don't think this is indicative of a real problem, and I don't think that we need to change code to make this warning disappear. > Modify the return judgment statement, use > "((val - min) < (val - max - 1))" to confirm that returns > true in “min <= val <= max” cases, false in other cases. That expression is far less clear than the existing code, so I do not think that is a good idea. > Fixes: 79d82cbcbb3d ("arm64/kexec: Test page size support with new TGRAN range values") What functional error does this fix? What configuration is broken? Thanks, Mark. > Signed-off-by: Lin Yujun > --- > arch/arm64/include/asm/cpufeature.h | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) > > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > index 03d1c9d7af82..0a6bda025141 100644 > --- a/arch/arm64/include/asm/cpufeature.h > +++ b/arch/arm64/include/asm/cpufeature.h > @@ -54,6 +54,9 @@ enum ftr_type { > #define FTR_VISIBLE_IF_IS_ENABLED(config) \ > (IS_ENABLED(config) ? FTR_VISIBLE : FTR_HIDDEN) > > +#define IN_RANGE_INCLUSIVE(val, min, max) \ > + (((val) - (min)) < ((val) - (max) - 1)) > + > struct arm64_ftr_bits { > bool sign; /* Value is signed ? */ > bool visible; > @@ -693,8 +696,9 @@ static inline bool system_supports_4kb_granule(void) > val = cpuid_feature_extract_unsigned_field(mmfr0, > ID_AA64MMFR0_EL1_TGRAN4_SHIFT); > > - return (val >= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN) && > - (val <= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX); > + return IN_RANGE_INCLUSIVE(val, > + ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN, > + ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX); > } > > static inline bool system_supports_64kb_granule(void) > @@ -706,8 +710,9 @@ static inline bool system_supports_64kb_granule(void) > val = cpuid_feature_extract_unsigned_field(mmfr0, > ID_AA64MMFR0_EL1_TGRAN64_SHIFT); > > - return (val >= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN) && > - (val <= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX); > + return IN_RANGE_INCLUSIVE(val, > + ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN, > + ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX); > } > > static inline bool system_supports_16kb_granule(void) > @@ -719,8 +724,9 @@ static inline bool system_supports_16kb_granule(void) > val = cpuid_feature_extract_unsigned_field(mmfr0, > ID_AA64MMFR0_EL1_TGRAN16_SHIFT); > > - return (val >= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN) && > - (val <= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX); > + return IN_RANGE_INCLUSIVE(val, > + ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN, > + ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX); > } > > static inline bool system_supports_mixed_endian_el0(void) > -- > 2.34.1 >