From: "Arnd Bergmann" <arnd@arndb.de>
To: "Anshuman Khandual" <anshuman.khandual@arm.com>,
linux-kernel@vger.kernel.org
Cc: "Ard Biesheuvel" <ardb@kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Yury Norov" <yury.norov@gmail.com>,
"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
Linux-Arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH V3 1/2] uapi: Define GENMASK_U128
Date: Tue, 20 Aug 2024 08:35:37 +0200 [thread overview]
Message-ID: <8b780eda-bb64-4baf-8e24-501baf8ed8db@app.fastmail.com> (raw)
In-Reply-To: <17020e56-b0a9-4705-8ee3-c675eca99490@arm.com>
On Tue, Aug 20, 2024, at 03:25, Anshuman Khandual wrote:
> On 8/19/24 12:43, Arnd Bergmann wrote:
>
> Should not the second shift operation warn about the possible
> overflow scenario ? But actually it does not. Or the compiler
> is too smart in detecting what's happening next in the overall
> equation and do the needful while creating the mask below the
> highest bit.
Not sure about the reasoning behind the compiler warning for
one but not the other, but I know that we rely on similar
behavior in places like:
#define upper_32_bits(n) ((u32)(((n) >> 16) >> 16))
which is intended to return a zero without a compiler
warning when passing an 'unsigned long' input on 32-bit
architectures.
Arnd
next prev parent reply other threads:[~2024-08-20 6:35 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-01 7:16 [PATCH V3 0/2] uapi: Add support for GENMASK_U128() Anshuman Khandual
2024-08-01 7:16 ` [PATCH V3 1/2] uapi: Define GENMASK_U128 Anshuman Khandual
2024-08-16 6:28 ` Anshuman Khandual
2024-08-17 13:57 ` Yury Norov
2024-08-19 3:18 ` Anshuman Khandual
2024-08-19 7:13 ` Arnd Bergmann
2024-08-20 1:25 ` Anshuman Khandual
2024-08-20 6:35 ` Arnd Bergmann [this message]
2024-08-01 7:16 ` [PATCH V3 2/2] lib/test_bits.c: Add tests for GENMASK_U128() Anshuman Khandual
2024-08-20 3:36 ` Anshuman Khandual
2024-08-01 14:43 ` [PATCH V3 0/2] uapi: Add support " Yury Norov
2024-08-02 1:30 ` Anshuman Khandual
2024-08-02 17:34 ` Yury Norov
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