linux-kernel - Re: [PATCH V2] of: fix clang -Wunsequenced for be32_to

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Date:   Tue, 30 Apr 2019 09:28:35 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Phong Tran <tranmanphong@...il.com>
Cc:     robh+dt@...nel.org, Frank Rowand <frowand.list@...il.com>,
        pantelis.antoniou@...sulko.com, David.Laight@...lab.com,
        hch@...radead.org, Nathan Chancellor <natechancellor@...il.com>,
        devicetree@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH V2] of: fix clang -Wunsequenced for be32_to_cpu()

On Tue, Apr 30, 2019 at 7:58 AM Phong Tran <tranmanphong@...il.com> wrote:
>
> Now, make the loop explicit to avoid clang warning.
>
> ./include/linux/of.h:238:37: warning: multiple unsequenced modifications
> to 'cell' [-Wunsequenced]
>                 r = (r << 32) | be32_to_cpu(*(cell++));
>                                                   ^~
> ./include/linux/byteorder/generic.h:95:21: note: expanded from macro
> 'be32_to_cpu'
>                     ^
> ./include/uapi/linux/byteorder/little_endian.h:40:59: note: expanded
> from macro '__be32_to_cpu'
>                                                           ^
> ./include/uapi/linux/swab.h:118:21: note: expanded from macro '__swab32'
>         ___constant_swab32(x) :                 \
>                            ^
> ./include/uapi/linux/swab.h:18:12: note: expanded from macro
> '___constant_swab32'
>         (((__u32)(x) & (__u32)0x000000ffUL) << 24) |            \
>                   ^
>
> Signed-off-by: Phong Tran <tranmanphong@...il.com>

Thanks for the patch.
Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/460
Suggested-by: David Laight <David.Laight@...LAB.COM>

> ---
>  include/linux/of.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/of.h b/include/linux/of.h
> index e240992e5cb6..71ca25ac01f6 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -234,8 +234,8 @@ extern struct device_node *of_find_all_nodes(struct device_node *prev);
>  static inline u64 of_read_number(const __be32 *cell, int size)
>  {
>         u64 r = 0;
> -       while (size--)
> -               r = (r << 32) | be32_to_cpu(*(cell++));
> +       for(; size--; cell++)
> +               r = (r << 32) | be32_to_cpu(*cell);
>         return r;
>  }
>
> --
> 2.21.0
>


--
Thanks,
~Nick Desaulniers