linux-kernel - Re: [PATCH] mm/vmstat: Fix -Wenum-enum-conversion warning in vmstat.h

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <a2e8a76a-9fad-4e3e-bce1-bf8a9d180464@app.fastmail.com>
Date: Fri, 11 Oct 2024 14:05:00 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Aleksei Vetrov" <vvvvvv@...gle.com>,
 "Nathan Chancellor" <nathan@...nel.org>
Cc: "Shivamurthy Shastri" <shivamurthy.shastri@...utronix.de>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Vlastimil Babka" <vbabka@...e.cz>, "Matthew Wilcox" <willy@...radead.org>,
 "Johannes Weiner" <hannes@...xchg.org>,
 "Anna-Maria Gleixner" <anna-maria@...utronix.de>,
 "Thomas Gleixner" <tglx@...utronix.de>, llvm@...ts.linux.dev
Subject: Re: [PATCH] mm/vmstat: Fix -Wenum-enum-conversion warning in vmstat.h

On Thu, Oct 10, 2024, at 10:40, Aleksei Vetrov wrote:
> On Mon, Oct 07, 2024 at 05:51:36PM -0700, Nathan Chancellor wrote:
>> For what it's worth, I never really saw Matthew's comment around what
>> value does this warning provide addressed. I was the one who originally
>> moved it into W=1 at the request of Arnd because he felt that instances
>> of this warning could be bugs and they should be audited.  However, I
>> have not seen many instances of this warning pop up in new code through
>> 0day build reports and the ones that I have seen seem to be intentional,
>> as they are using enums like integral values, such as here. If that is
>> just going to result in a bunch of patches like this adding unnecessary
>> casts, I think it would just be better to consider disabling this
>> warning altogether or at the very least, moving it to W=2 (which is for
>> warnings that are noisy but might contain bugs), since more people are
>> using W=1 as their normal build configuration nowadays.
>
> If time has proven that this warning has never found an unintended enum
> conversion, then it is worth to disable it for everyone. As you said in
> the original thread ([PATCH] kbuild: Disable two Clang specific
> enumeration warnings), W=2 is not run by any CI, so I would prefer to
> disable it completely.
>
> Alternatives considered:
>
> * Enable -Wenum-enum-conversion only for 0day build reports through
>   KCFLAGS. It will eliminate noise for regular users while keeping
>   developers informed about new instances of this warning.
> * -Wno-error=enum-enum-conversion to keep warning but don't block
>   compilation for CONFIG_WERROR users.
>
> Arnd Bergmann, what do you think? Have you found it useful after all?

I'm fairly sure I saw users mix up 'dma_data_direction' with
'dma_transfer_direction' and unrelated enum-enum mixups in
amdgpu. There were probably more.

I think what happened is that in clang-18 and earlier, the
warning option caught mistakes of passing the wrong enum 
to a function and a few others, but it did not catch arithmetic
operations between enums, so clang-19 now produces a lot more
output than older versions, and I don't think we can
control those independently.

       Arnd