From: Alice Ryhl <aliceryhl@google.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: Andrew Ballance <andrewjballance@gmail.com>,
Joel Fernandes <joelagnelf@nvidia.com>,
rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
John Hubbard <jhubbard@nvidia.com>,
Alexandre Courbot <acourbot@nvidia.com>,
Timur Tabi <ttabi@nvidia.com>,
Alistair Popple <apopple@nvidia.com>,
Miguel Ojeda <ojeda@kernel.org>
Subject: Re: Printing with overflow checks can cause modpost errors
Date: Fri, 12 Sep 2025 11:45:16 +0200 [thread overview]
Message-ID: <CAH5fLgiP2DRcGy04YdsWS9+N1=_CCNEtAGrCn31vUHjnDLW9xw@mail.gmail.com> (raw)
In-Reply-To: <CANiq72kZgZdU4Dut3rmcWT-cujyJaP_99ekis_XdfQ-7LmgZ5Q@mail.gmail.com>
On Fri, Sep 12, 2025 at 10:28 AM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Fri, Sep 12, 2025 at 6:08 AM Andrew Ballance
> <andrewjballance@gmail.com> wrote:
> >
> > The pointer passed is const so rustc should assume that the c side does
> > not change offset, but looks like rustc does not do that.
>
> That is not possible -- a const pointer does not guarantee the value
> will not be changed.
I believe this code is using an immutable reference and not just a
pointer, so it would be UB to use it to write to `offset`, and so it
would be valid to assume it has not changed. But I think that in most
scenarios, Rust only optimizes using that information when the
reference appears as a function argument, which is not the case here.
Alice
next prev parent reply other threads:[~2025-09-12 9:45 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-11 21:31 Printing with overflow checks can cause modpost errors Joel Fernandes
2025-09-12 0:27 ` Andrew Ballance
2025-09-12 2:53 ` Joel Fernandes
2025-09-12 4:08 ` Andrew Ballance
2025-09-12 8:27 ` Miguel Ojeda
2025-09-12 9:45 ` Alice Ryhl [this message]
2025-09-12 10:08 ` Miguel Ojeda
2025-09-16 10:32 ` Joel Fernandes
2025-09-16 10:48 ` Joel Fernandes
2025-09-16 18:52 ` Joel Fernandes
2025-09-17 23:18 ` Timur Tabi
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