Messages in this thread |  | | Date | Tue, 14 Aug 2018 16:11:06 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] bitfield: avoid gcc-8 -Wint-in-bool-context warning |
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On Tue, 14 Aug 2018 00:09:34 +0200 Arnd Bergmann <arnd@arndb.de> wrote:
> 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,
Newer compilers will previously be used on older kernels, so I'll add a cc:stable here.
> 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@arndb.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, \
I'm not understanding how a switch from !x to x==0 can fix anything. Help!
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