linux-kernel - Re: [PATCH] soc: renesas: rmobile-sysc: fix -Wvoid-pointer-to-enum-cast warning

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Date:   Wed, 30 Aug 2023 10:24:56 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Magnus Damm <magnus.damm@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] soc: renesas: rmobile-sysc: fix -Wvoid-pointer-to-enum-cast
 warning

Hi Justin,

On Tue, Aug 15, 2023 at 12:11 AM Justin Stitt <justinstitt@...gle.com> wrote:
> When building with clang 18 I see the following warning:
> |      drivers/soc/renesas/rmobile-sysc.c:193:22: warning: cast to smaller integer
> |               type 'enum pd_types' from 'const void *' [-Wvoid-pointer-to-enum-cast]
> |        193 |                 add_special_pd(np, (enum pd_types)id->data);
>
> This is due to the fact that `id->data` is a void* and `enum pd_types`
> has the size of an integer. This cast from pointer-width to int-width
> causes truncation and possible data loss. Instead, cast to `uintptr_t`
> which has the same width as void*.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1910
> Reported-by: Nathan Chancellor <nathan@...nel.org>

scripts/checkpatch.pl:

    WARNING: Reported-by: should be immediately followed by Closes:
with a URL to the report

Hence changing the Link: tag to a Closes: tag.

> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Note: It should be noted that there is likely no data loss occurring in
> this case since the enum only has a few fields. The narrowing cast from
> pointer to int will not lose any data.

Indeed, the theoretical narrowing could only happen on a 64-bit
platform, while this driver is only used on arm32.

Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
i.e. will queue in renesas-devel for v6.7.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds