From: David Laight <David.Laight@ACULAB.COM>
To: 'Arnd Bergmann' <arnd@kernel.org>, Will Deacon <will@kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
Arnd Bergmann <arnd@arndb.de>, Matt Evans <mev@rivosinc.com>
Cc: Boqun Feng <boqun.feng@gmail.com>,
Mark Rutland <mark.rutland@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: RE: [PATCH] asm-generic: avoid __generic_cmpxchg_local warnings
Date: Thu, 2 Mar 2023 16:40:00 +0000 [thread overview]
Message-ID: <60996fd3604b403ab67e8f73854264ee@AcuMS.aculab.com> (raw)
In-Reply-To: <20230302090032.3740505-1-arnd@kernel.org>
...
> I had another look at why the cast is even needed for atomic_cmpxchg(),
> and as Matt describes the problem here is that atomic_t contains a
> signed 'int', but cmpxchg() takes an 'unsigned long' argument, and
> converting between the two leads to a 64-bit sign-extension of
> negative 32-bit atomics.
How about:
signed_var + 0u + 0ull;
Converts 32bit signed to 64bit unsigned without sign extension.
Compiler will throw it all away if not needed.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
prev parent reply other threads:[~2023-03-02 16:40 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-02 9:00 [PATCH] asm-generic: avoid __generic_cmpxchg_local warnings Arnd Bergmann
2023-03-02 16:40 ` David Laight [this message]
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