linux-kernel - Re: [PATCH v5 13/36] bit_spinlock: Support Clang's context analysis

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Message-ID: <3b070057-5fda-410e-a047-d9061d56a82f@acm.org>
Date: Fri, 19 Dec 2025 12:47:43 -0800
From: Bart Van Assche <bvanassche@....org>
To: Marco Elver <elver@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
 Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...nel.org>,
 Will Deacon <will@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
 Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
 Chris Li <sparse@...isli.org>, "Paul E. McKenney" <paulmck@...nel.org>,
 Alexander Potapenko <glider@...gle.com>, Arnd Bergmann <arnd@...db.de>,
 Christoph Hellwig <hch@....de>, Dmitry Vyukov <dvyukov@...gle.com>,
 Eric Dumazet <edumazet@...gle.com>, Frederic Weisbecker
 <frederic@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Herbert Xu <herbert@...dor.apana.org.au>, Ian Rogers <irogers@...gle.com>,
 Jann Horn <jannh@...gle.com>, Joel Fernandes <joelagnelf@...dia.com>,
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 <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>,
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Subject: Re: [PATCH v5 13/36] bit_spinlock: Support Clang's context analysis

On 12/19/25 7:40 AM, Marco Elver wrote:
> +/*
> + * For static context analysis, we need a unique token for each possible bit
> + * that can be used as a bit_spinlock. The easiest way to do that is to create a
> + * fake context that we can cast to with the __bitlock(bitnum, addr) macro
> + * below, which will give us unique instances for each (bit, addr) pair that the
> + * static analysis can use.
> + */
> +context_lock_struct(__context_bitlock) { };
> +#define __bitlock(bitnum, addr) (struct __context_bitlock *)(bitnum + (addr))

Will this cause static analyzers to complain about out-of-bounds
accesses for (bitnum + (addr)), which is equivalent to &(addr)[bitnum]?

Thanks,

Bart.