linux-kernel - Re: [PATCH] bitfield: avoid gcc-8 -Wint-in-bool-context warning

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Date:   Tue, 14 Aug 2018 08:57:34 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Berg <johannes@...solutions.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bitfield: avoid gcc-8 -Wint-in-bool-context warning

2018-08-14 7:09 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
> Passing an enum into FIELD_GET() produces a long but harmless warning on
> newer compilers:
>
>                  from include/linux/linkage.h:7,
>                  from include/linux/kernel.h:7,
>                  from include/linux/skbuff.h:17,
>                  from include/linux/if_ether.h:23,
>                  from include/linux/etherdevice.h:25,
>                  from drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c:63:
> drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c: In function 'iwl_mvm_rx_mpdu_mq':
> include/linux/bitfield.h:56:20: error: enum constant in boolean context [-Werror=int-in-bool-context]
>    BUILD_BUG_ON_MSG(!(_mask), _pfx "mask is zero"); \
>                     ^
> ...
> include/linux/bitfield.h:103:3: note: in expansion of macro '__BF_FIELD_CHECK'
>    __BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: "); \
>    ^~~~~~~~~~~~~~~~
> drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c:1025:21: note: in expansion of macro 'FIELD_GET'
>     le16_encode_bits(FIELD_GET(IWL_RX_HE_PHY_SIBG_SYM_OR_USER_NUM_MASK,


How about fixing the root cause
in drivers/net/wireless/intel/iwlwifi/fw/api/rx.h ?


#define IWL_RX_HE_PHY_SIBG_SYM_OR_USER_NUM_MASK   0x1e00000000ULL


enum iwl_rx_he_phy looks really strange.



Passing enum to FIELD_GET is odd,
so I prefer keeping this warned.



> The problem here is that the caller has no idea how the macro gets
> expanding, leading to a false-positive. It can be trivially avoided
> by doing a comparison against zero.
>
> This only recently started appearing as the iwlwifi driver was patched
> to use FIELD_GET.
>
> Fixes: 514c30696fbc ("iwlwifi: add support for IEEE802.11ax")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  include/linux/bitfield.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
> index 65a6981eef7b..3f1ef4450a7c 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -53,7 +53,7 @@
>         ({                                                              \
>                 BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),          \
>                                  _pfx "mask is not constant");          \
> -               BUILD_BUG_ON_MSG(!(_mask), _pfx "mask is zero");        \
> +               BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");    \
>                 BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?           \
>                                  ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
>                                  _pfx "value too large for the field"); \
> --
> 2.18.0
>



-- 
Best Regards
Masahiro Yamada