From 9c10cba536874641bbc70a53588d6a59c9292e2e Mon Sep 17 00:00:00 2001 From: Geert Uytterhoeven Date: Fri, 3 Jul 2026 14:56:11 +0300 Subject: bitfield: Add less-checking __FIELD_{GET,PREP}() The BUILD_BUG_ON_MSG() check against "~0ull" works only with "unsigned (long) long" _mask types. For constant masks, that condition is usually met, as GENMASK() yields an UL value. The few places where the constant mask is stored in an intermediate variable were fixed by changing the variable type to u64. However, for non-constant masks, smaller unsigned types should be valid, too, but currently lead to "result of comparison of constant 18446744073709551615 with expression of type ... is always false"-warnings with clang and W=1. Hence refactor the __BF_FIELD_CHECK() helper, and factor out __FIELD_{GET,PREP}(). The later lack the single problematic check, but are otherwise identical to FIELD_{GET,PREP}(), and are intended to be used in the fully non-const variants later. Signed-off-by: Geert Uytterhoeven Signed-off-by: Yury Norov (NVIDIA) [Linux commit: 2a6c045640c38a407a39cd40c3c4d8dd2fd89aa8] Signed-off-by: Mikhail Kshevetskiy Reviewed-by: David Lechner Reviewed-by: Simon Glass Signed-off-by: Scott Wood Acked-by: Gerald Van Baren Reviewed-by: Andre Przywara Signed-off-by: Masahiro Yamada --- include/linux/bitfield.h | 36 ++++++++++++++++++++++++++++-------- 1 file changed, 28 insertions(+), 8 deletions(-) (limited to 'include/linux/bitfield.h') diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h index 63928f17322..ef81901bc41 100644 --- a/include/linux/bitfield.h +++ b/include/linux/bitfield.h @@ -60,7 +60,7 @@ #define __bf_cast_unsigned(type, x) ((__unsigned_scalar_typeof(type))(x)) -#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx) \ +#define __BF_FIELD_CHECK_MASK(_mask, _val, _pfx) \ ({ \ BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \ _pfx "mask is not constant"); \ @@ -69,13 +69,33 @@ ~((_mask) >> __bf_shf(_mask)) & \ (0 + (_val)) : 0, \ _pfx "value too large for the field"); \ - BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \ - __bf_cast_unsigned(_reg, ~0ull), \ - _pfx "type of reg too small for mask"); \ __BUILD_BUG_ON_NOT_POWER_OF_2((_mask) + \ (1ULL << __bf_shf(_mask))); \ }) +#define __BF_FIELD_CHECK_REG(mask, reg, pfx) \ + BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) > \ + __bf_cast_unsigned(reg, ~0ull), \ + pfx "type of reg too small for mask") + +#define __BF_FIELD_CHECK(mask, reg, val, pfx) \ + ({ \ + __BF_FIELD_CHECK_MASK(mask, val, pfx); \ + __BF_FIELD_CHECK_REG(mask, reg, pfx); \ + }) + +#define __FIELD_PREP(mask, val, pfx) \ + ({ \ + __BF_FIELD_CHECK_MASK(mask, val, pfx); \ + ((typeof(mask))(val) << __bf_shf(mask)) & (mask); \ + }) + +#define __FIELD_GET(mask, reg, pfx) \ + ({ \ + __BF_FIELD_CHECK_MASK(mask, 0U, pfx); \ + (typeof(mask))(((reg) & (mask)) >> __bf_shf(mask)); \ + }) + /** * FIELD_MAX() - produce the maximum value representable by a field * @_mask: shifted mask defining the field's length and position @@ -112,8 +132,8 @@ */ #define FIELD_PREP(_mask, _val) \ ({ \ - __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \ - ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \ + __BF_FIELD_CHECK_REG(_mask, 0ULL, "FIELD_PREP: "); \ + __FIELD_PREP(_mask, _val, "FIELD_PREP: "); \ }) #define __BF_CHECK_POW2(n) BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0) @@ -152,8 +172,8 @@ */ #define FIELD_GET(_mask, _reg) \ ({ \ - __BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: "); \ - (typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask)); \ + __BF_FIELD_CHECK_REG(_mask, _reg, "FIELD_GET: "); \ + __FIELD_GET(_mask, _reg, "FIELD_GET: "); \ }) extern void __compiletime_error("value doesn't fit into mask") -- cgit v1.3.1 From da10fca9b062bde09144d65a0559676c658ac0ae Mon Sep 17 00:00:00 2001 From: Geert Uytterhoeven Date: Fri, 3 Jul 2026 14:56:12 +0300 Subject: bitfield: Add non-constant field_{prep, get}() helpers MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The existing FIELD_{GET,PREP}() macros are limited to compile-time constants. However, it is very common to prepare or extract bitfield elements where the bitfield mask is not a compile-time constant. To avoid this limitation, the AT91 clock driver and several other drivers already have their own non-const field_{prep,get}() macros. Make them available for general use by adding them to , and improve them slightly: 1. Avoid evaluating macro parameters more than once, 2. Replace "ffs() - 1" by "__ffs()", 3. Support 64-bit use on 32-bit architectures, 4. Wire field_{get,prep}() to FIELD_{GET,PREP}() when mask is actually constant. This is deliberately not merged into the existing FIELD_{GET,PREP}() macros, as people expressed the desire to keep stricter variants for increased safety, or for performance critical paths. Yury: use __mask within new macros. Signed-off-by: Geert Uytterhoeven Acked-by: Alexandre Belloni Acked-by: Jonathan Cameron Acked-by: Crt Mori Acked-by: Nuno Sá Acked-by: Richard Genoud Reviewed-by: Andy Shevchenko Reviewed-by: Yury Norov (NVIDIA) Signed-off-by: Yury Norov (NVIDIA) [Linux commit: c1c6ab80b25c8db1e2ef5ae3ac8075d2c242ae13] Signed-off-by: Mikhail Kshevetskiy Reviewed-by: David Lechner Reviewed-by: Simon Glass --- include/linux/bitfield.h | 59 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) (limited to 'include/linux/bitfield.h') diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h index ef81901bc41..18cf57aeb2c 100644 --- a/include/linux/bitfield.h +++ b/include/linux/bitfield.h @@ -16,6 +16,7 @@ * FIELD_{GET,PREP} macros take as first parameter shifted mask * from which they extract the base mask and shift amount. * Mask must be a compilation time constant. + * field_{get,prep} are variants that take a non-const mask. * * Example: * @@ -223,4 +224,62 @@ __MAKE_OP(64) #undef __MAKE_OP #undef ____MAKE_OP +#define __field_prep(mask, val) \ + ({ \ + __auto_type __mask = (mask); \ + typeof(__mask) __val = (val); \ + unsigned int __shift = BITS_PER_TYPE(__mask) <= 32 ? \ + __ffs(__mask) : __ffs64(__mask); \ + (__val << __shift) & __mask; \ + }) + +#define __field_get(mask, reg) \ + ({ \ + __auto_type __mask = (mask); \ + typeof(__mask) __reg = (reg); \ + unsigned int __shift = BITS_PER_TYPE(__mask) <= 32 ? \ + __ffs(__mask) : __ffs64(__mask); \ + (__reg & __mask) >> __shift; \ + }) + +/** + * field_prep() - prepare a bitfield element + * @mask: shifted mask defining the field's length and position, must be + * non-zero + * @val: value to put in the field + * + * Return: field value masked and shifted to its final destination + * + * field_prep() masks and shifts up the value. The result should be + * combined with other fields of the bitfield using logical OR. + * Unlike FIELD_PREP(), @mask is not limited to a compile-time constant. + * Typical usage patterns are a value stored in a table, or calculated by + * shifting a constant by a variable number of bits. + * If you want to ensure that @mask is a compile-time constant, please use + * FIELD_PREP() directly instead. + */ +#define field_prep(mask, val) \ + (__builtin_constant_p(mask) ? __FIELD_PREP(mask, val, "field_prep: ") \ + : __field_prep(mask, val)) + +/** + * field_get() - extract a bitfield element + * @mask: shifted mask defining the field's length and position, must be + * non-zero + * @reg: value of entire bitfield + * + * Return: extracted field value + * + * field_get() extracts the field specified by @mask from the + * bitfield passed in as @reg by masking and shifting it down. + * Unlike FIELD_GET(), @mask is not limited to a compile-time constant. + * Typical usage patterns are a value stored in a table, or calculated by + * shifting a constant by a variable number of bits. + * If you want to ensure that @mask is a compile-time constant, please use + * FIELD_GET() directly instead. + */ +#define field_get(mask, reg) \ + (__builtin_constant_p(mask) ? __FIELD_GET(mask, reg, "field_get: ") \ + : __field_get(mask, reg)) + #endif -- cgit v1.3.1