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bitfield: avoid gcc-8 -Wint-in-bool-context warning 

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,

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.

Link: http://lkml.kernel.org/r/20180813220950.194841-1-arnd@arndb.de
Fixes: 514c30696f ("iwlwifi: add support for IEEE802.11ax")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Arnd Bergmann 2018-08-17 15:43:36 -07:00 committed by Linus Torvalds
parent 6ed191ca90
commit e36488c83b
1 changed files with 1 additions and 1 deletions
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2
include/linux/bitfield.h
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@ -53,7 +53,7 @@
({ \ ({ \
BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \ BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \
_pfx "mask is not constant"); \ _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) ? \ BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \
~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \ ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
_pfx "value too large for the field"); \ _pfx "value too large for the field"); \