linux.git/include/linux/bitfield.h, branch v6.12.80

bitfield: suppress "dubious: x & !y" sparse warning

2024-02-28T11:53:39+00:00

There's a somewhat common pattern of using FIELD_PREP()
even for single bits, e.g.

 cmd->info1 |= FIELD_PREP(HTT_SRNG_SETUP_CMD_INFO1_RING_FLAGS_MSI_SWAP,
                          !!(params.flags & HAL_SRNG_FLAGS_MSI_SWAP));

which might as well be written as

 if (params.flags & HAL_SRNG_FLAGS_MSI_SWAP)
   cmd->info1 |= HTT_SRNG_SETUP_CMD_INFO1_RING_FLAGS_MSI_SWAP;

(since info1 is fully initialized to start with), but in
a long chain of FIELD_PREP() this really seems fine.

However, it triggers a sparse warning, in the check in
the macro for whether a constant value fits into the mask,
as this contains a "& (_val)". In this case, this really
is always intentional, so just suppress the warning by
adding "0+" to the expression, indicating explicitly that
this is correct.

Signed-off-by: Johannes Berg 
Signed-off-by: Kalle Valo 
Link: https://msgid.link/20240223100146.d243b6b1a9a1.I033828b1187c6bccf086e31400f7e933bb8373e7@changeid

bitfield: add FIELD_PREP_CONST()

2023-01-19T13:46:25+00:00

Neither FIELD_PREP() nor *_encode_bits() can be used
in constant contexts (such as initializers), but we
don't want to define shift constants for all masks
just for use in initializers, and having checks that
the values fit is also useful.

Therefore, add FIELD_PREP_CONST() which is a smaller
version of FIELD_PREP() that can only take constant
arguments and has less friendly (but not less strict)
error checks, and expands to a constant value.

Signed-off-by: Johannes Berg 
Link: https://lore.kernel.org/r/20230118142652.53f20593504b.Iaeea0aee77a6493d70e573b4aa55c91c00e01e4b@changeid
Signed-off-by: Johannes Berg

bitfield: add explicit inclusions to the example

2022-03-24T02:00:33+00:00

It's not obvious that bitfield.h doesn't guarantee the bits.h inclusion
and the example in the former is confusing.  Some developers think that
it's okay to just include bitfield.h to get it working.  Change example
to explicitly include necessary headers in order to avoid confusion.

Link: https://lkml.kernel.org/r/20220207123341.47533-1-andriy.shevchenko@linux.intel.com
Fixes: 3e9b3112ec74 ("add basic register-field manipulation macros")
Depends-on: 8bd9cb51daac ("locking/atomics, asm-generic: Move some macros from  to a new  file")
Signed-off-by: Andy Shevchenko 
Reported-by: Jan Dąbroś 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

bitfield.h: Fix "type of reg too small for mask" test

2021-12-11T08:09:45+00:00

The test: 'mask > (typeof(_reg))~0ull' only works correctly when both
sides are unsigned, consider:

 - 0xff000000 vs (int)~0ull
 - 0x000000ff vs (int)~0ull

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Josh Poimboeuf 
Link: https://lore.kernel.org/r/20211110101324.950210584@infradead.org

bitfield.h: don't compile-time validate _val in FIELD_FIT

2020-08-10T19:16:51+00:00

When ur_load_imm_any() is inlined into jeq_imm(), it's possible for the
compiler to deduce a case where _val can only have the value of -1 at
compile time. Specifically,

/* struct bpf_insn: _s32 imm */
u64 imm = insn->imm; /* sign extend */
if (imm >> 32) { /* non-zero only if insn->imm is negative */
  /* inlined from ur_load_imm_any */
  u32 __imm = imm >> 32; /* therefore, always 0xffffffff */
  if (__builtin_constant_p(__imm) && __imm > 255)
    compiletime_assert_XXX()

This can result in tripping a BUILD_BUG_ON() in __BF_FIELD_CHECK() that
checks that a given value is representable in one byte (interpreted as
unsigned).

FIELD_FIT() should return true or false at runtime for whether a value
can fit for not. Don't break the build over a value that's too large for
the mask. We'd prefer to keep the inlining and compiler optimizations
though we know this case will always return false.

Cc: stable@vger.kernel.org
Fixes: 1697599ee301a ("bitfield.h: add FIELD_FIT() helper")
Link: https://lore.kernel.org/kernel-hardening/CAK7LNASvb0UDJ0U5wkYYRzTAdnEs64HjXpEUL7d=V0CXiAXcNw@mail.gmail.com/
Reported-by: Masahiro Yamada 
Debugged-by: Sami Tolvanen 
Signed-off-by: Jakub Kicinski 
Signed-off-by: Nick Desaulniers 
Signed-off-by: David S. Miller

bitfield.h: add FIELD_MAX() and field_max()

2020-03-12T22:48:37+00:00

Define FIELD_MAX(), which supplies the maximum value that can be
represented by a field value.  Define field_max() as well, to go
along with the lower-case forms of the field mask functions.

Signed-off-by: Alex Elder 
Acked-by: Jakub Kicinski 
Signed-off-by: David S. Miller

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174

2019-05-30T18:26:41+00:00

Based on 1 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license version 2 as
  published by the free software foundation this program is
  distributed in the hope that it will be useful but without any
  warranty without even the implied warranty of merchantability or
  fitness for a particular purpose see the gnu general public license
  for more details

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 655 file(s).

Signed-off-by: Thomas Gleixner 
Reviewed-by: Allison Randal 
Reviewed-by: Kate Stewart 
Reviewed-by: Richard Fontana 
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070034.575739538@linutronix.de
Signed-off-by: Greg Kroah-Hartman

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

2018-08-17T23:20:27+00:00

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: 514c30696fbc ("iwlwifi: add support for IEEE802.11ax")
Signed-off-by: Arnd Bergmann 
Cc: Masahiro Yamada 
Cc: Johannes Berg 
Cc: Jakub Kicinski 
Cc: Andy Shevchenko 
Cc: Al Viro 
Cc: David Laight 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

bitfield: add u8 helpers

2018-06-27T15:58:49+00:00

There's no reason why we shouldn't pack/unpack bits into/from
u8 values/registers/etc., so add u8 helpers.

Use the ____MAKE_OP() macro directly to avoid having nonsense
le8_encode_bits() and similar functions.

Reviewed-by: Andy Shevchenko 
Signed-off-by: Johannes Berg 
Signed-off-by: Kalle Valo

bitfield: fix *_encode_bits()

2018-06-27T15:58:48+00:00

There's a bug in *_encode_bits() in using ~field_multiplier() for
the check whether or not the constant value fits into the field,
this is wrong and clearly ~field_mask() was intended. This was
triggering for me for both constant and non-constant values.

Additionally, make this case actually into an compile error.
Declaring the extern function that will never exist with just a
warning is pointless as then later we'll just get a link error.

While at it, also fix the indentation in those lines I'm touching.

Finally, as suggested by Andy Shevchenko, add some tests and for
that introduce also u8 helpers. The tests don't compile without
the fix, showing that it's necessary.

Fixes: 00b0c9b82663 ("Add primitives for manipulating bitfields both in host- and fixed-endian.")
Reviewed-by: Andy Shevchenko 
Signed-off-by: Johannes Berg 
Signed-off-by: Kalle Valo