linux-kernel - Re: [PATCH v8 5/7] rust: str: add radix prefixed integer parsing functions

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Message-ID: <87zfheddk8.fsf@kernel.org>
Date: Fri, 21 Mar 2025 08:53:59 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Miguel Ojeda" <miguel.ojeda.sandonis@...il.com>
Cc: "Miguel Ojeda" <ojeda@...nel.org>,  "Alex Gaynor"
 <alex.gaynor@...il.com>,  "Boqun Feng" <boqun.feng@...il.com>,  "Gary Guo"
 <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,  "Benno
 Lossin" <benno.lossin@...ton.me>,  "Alice Ryhl" <aliceryhl@...gle.com>,
  "Masahiro Yamada" <masahiroy@...nel.org>,  "Nathan Chancellor"
 <nathan@...nel.org>,  "Nicolas Schier" <nicolas@...sle.eu>,  "Luis
 Chamberlain" <mcgrof@...nel.org>,  "Trevor Gross" <tmgross@...ch.edu>,
  "Adam Bratschi-Kaye" <ark.email@...il.com>,
  <rust-for-linux@...r.kernel.org>,  <linux-kernel@...r.kernel.org>,
  <linux-kbuild@...r.kernel.org>,  "Petr Pavlu" <petr.pavlu@...e.com>,
  "Sami Tolvanen" <samitolvanen@...gle.com>,  "Daniel Gomez"
 <da.gomez@...sung.com>,  "Simona Vetter" <simona.vetter@...ll.ch>,  "Greg
 KH" <gregkh@...uxfoundation.org>,  "Fiona Behrens" <me@...enk.dev>,
  "Daniel Almeida" <daniel.almeida@...labora.com>,
  <linux-modules@...r.kernel.org>
Subject: Re: [PATCH v8 5/7] rust: str: add radix prefixed integer parsing
 functions

"Miguel Ojeda" <miguel.ojeda.sandonis@...il.com> writes:

> On Thu, Feb 27, 2025 at 3:39 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>>
>> +                    // SAFETY: We checked that `val` will fit in `Self` above.
>> +                    let val: Self = unsafe { val.try_into().unwrap_unchecked() };
>
> This is wrong -- `val` can be the maximum, and thus it does not fit
> since it is 2's complement, even if later the complement would.
>
> In fact, it is caught by the doctest when run with debug assertions enabled:
>
>    /// assert_eq!(Ok(-128), i8::from_str(b_str!("-128")));
>
> We try to put 128 into `i8`, which of course does not work...

Thanks for catching this! I have to start running tests with debug
assertions, it makes no sense not to do so.

I'll send a new version now, hope it will make the cut.


Best regards,
Andreas Hindborg