From 31299a5e0211241171b2222c5633aad4763bf700 Mon Sep 17 00:00:00 2001 From: Vincent Mailhol Date: Wed, 26 Mar 2025 00:59:56 +0900 Subject: bits: add comments and newlines to #if, #else and #endif directives This is a preparation for the upcoming GENMASK_U*() and BIT_U*() changes. After introducing those new macros, there will be a lot of scrolling between the #if, #else and #endif. Add a comment to the #else and #endif preprocessor macros to help keep track of which context we are in. Also, add new lines to better visually separate the non-asm and asm sections. Signed-off-by: Vincent Mailhol Reviewed-by: Andy Shevchenko Signed-off-by: Yury Norov --- include/linux/bits.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'include/linux/bits.h') diff --git a/include/linux/bits.h b/include/linux/bits.h index 14fd0ca9a6cd..e1e517769140 100644 --- a/include/linux/bits.h +++ b/include/linux/bits.h @@ -19,16 +19,21 @@ * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. */ #if !defined(__ASSEMBLY__) + #include #include + #define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(const_true((l) > (h))) -#else + +#else /* defined(__ASSEMBLY__) */ + /* * BUILD_BUG_ON_ZERO is not available in h files included from asm files, * disable the input check if that is the case. */ #define GENMASK_INPUT_CHECK(h, l) 0 -#endif + +#endif /* !defined(__ASSEMBLY__) */ #define GENMASK(h, l) \ (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) -- cgit v1.2.3 From 19408200c094858d952a90bf4977733dc89a4df5 Mon Sep 17 00:00:00 2001 From: Vincent Mailhol Date: Wed, 26 Mar 2025 00:59:57 +0900 Subject: bits: introduce fixed-type GENMASK_U*() Add GENMASK_TYPE() which generalizes __GENMASK() to support different types, and implement fixed-types versions of GENMASK() based on it. The fixed-type version allows more strict checks to the min/max values accepted, which is useful for defining registers like implemented by i915 and xe drivers with their REG_GENMASK*() macros. The strict checks rely on shift-count-overflow compiler check to fail the build if a number outside of the range allowed is passed. Example: #define FOO_MASK GENMASK_U32(33, 4) will generate a warning like: include/linux/bits.h:51:27: error: right shift count >= width of type [-Werror=shift-count-overflow] 51 | type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h))))) | ^~ The result is casted to the corresponding fixed width type. For example, GENMASK_U8() returns an u8. Note that because of the C promotion rules, GENMASK_U8() and GENMASK_U16() will immediately be promoted to int if used in an expression. Regardless, the main goal is not to get the correct type, but rather to enforce more checks at compile time. While GENMASK_TYPE() is crafted to cover all variants, including the already existing GENMASK(), GENMASK_ULL() and GENMASK_U128(), for the moment, only use it for the newly introduced GENMASK_U*(). The consolidation will be done in a separate change. Co-developed-by: Yury Norov Signed-off-by: Lucas De Marchi Acked-by: Jani Nikula Signed-off-by: Vincent Mailhol Reviewed-by: Andy Shevchenko Signed-off-by: Yury Norov --- include/linux/bits.h | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) (limited to 'include/linux/bits.h') diff --git a/include/linux/bits.h b/include/linux/bits.h index e1e517769140..9718c5ae5fc3 100644 --- a/include/linux/bits.h +++ b/include/linux/bits.h @@ -12,6 +12,7 @@ #define BIT_ULL_MASK(nr) (ULL(1) << ((nr) % BITS_PER_LONG_LONG)) #define BIT_ULL_WORD(nr) ((nr) / BITS_PER_LONG_LONG) #define BITS_PER_BYTE 8 +#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) /* * Create a contiguous bitmask starting at bit position @l and ending at @@ -20,11 +21,40 @@ */ #if !defined(__ASSEMBLY__) +/* + * Missing asm support + * + * GENMASK_U*() depend on BITS_PER_TYPE() which relies on sizeof(), + * something not available in asm. Nevertheless, fixed width integers is a C + * concept. Assembly code can rely on the long and long long versions instead. + */ + #include #include +#include #define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(const_true((l) > (h))) +/* + * Generate a mask for the specified type @t. Additional checks are made to + * guarantee the value returned fits in that type, relying on + * -Wshift-count-overflow compiler check to detect incompatible arguments. + * For example, all these create build errors or warnings: + * + * - GENMASK(15, 20): wrong argument order + * - GENMASK(72, 15): doesn't fit unsigned long + * - GENMASK_U32(33, 15): doesn't fit in a u32 + */ +#define GENMASK_TYPE(t, h, l) \ + ((t)(GENMASK_INPUT_CHECK(h, l) + \ + (type_max(t) << (l) & \ + type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h))))) + +#define GENMASK_U8(h, l) GENMASK_TYPE(u8, h, l) +#define GENMASK_U16(h, l) GENMASK_TYPE(u16, h, l) +#define GENMASK_U32(h, l) GENMASK_TYPE(u32, h, l) +#define GENMASK_U64(h, l) GENMASK_TYPE(u64, h, l) + #else /* defined(__ASSEMBLY__) */ /* -- cgit v1.2.3 From 5b572e8a9f3dcd6e3ba80ec5b5ec85472c88cb4c Mon Sep 17 00:00:00 2001 From: Lucas De Marchi Date: Wed, 26 Mar 2025 00:59:58 +0900 Subject: bits: introduce fixed-type BIT_U*() Implement fixed-type BIT_U*() to help drivers add stricter checks, like it was done for GENMASK_U*(). Signed-off-by: Lucas De Marchi Acked-by: Jani Nikula Co-developed-by: Vincent Mailhol Signed-off-by: Vincent Mailhol Reviewed-by: Andy Shevchenko Signed-off-by: Yury Norov --- include/linux/bits.h | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) (limited to 'include/linux/bits.h') diff --git a/include/linux/bits.h b/include/linux/bits.h index 9718c5ae5fc3..7ad056219115 100644 --- a/include/linux/bits.h +++ b/include/linux/bits.h @@ -24,7 +24,7 @@ /* * Missing asm support * - * GENMASK_U*() depend on BITS_PER_TYPE() which relies on sizeof(), + * GENMASK_U*() and BIT_U*() depend on BITS_PER_TYPE() which relies on sizeof(), * something not available in asm. Nevertheless, fixed width integers is a C * concept. Assembly code can rely on the long and long long versions instead. */ @@ -55,6 +55,24 @@ #define GENMASK_U32(h, l) GENMASK_TYPE(u32, h, l) #define GENMASK_U64(h, l) GENMASK_TYPE(u64, h, l) +/* + * Fixed-type variants of BIT(), with additional checks like GENMASK_TYPE(). The + * following examples generate compiler warnings due to -Wshift-count-overflow: + * + * - BIT_U8(8) + * - BIT_U32(-1) + * - BIT_U32(40) + */ +#define BIT_INPUT_CHECK(type, nr) \ + BUILD_BUG_ON_ZERO(const_true((nr) >= BITS_PER_TYPE(type))) + +#define BIT_TYPE(type, nr) ((type)(BIT_INPUT_CHECK(type, nr) + BIT_ULL(nr))) + +#define BIT_U8(nr) BIT_TYPE(u8, nr) +#define BIT_U16(nr) BIT_TYPE(u16, nr) +#define BIT_U32(nr) BIT_TYPE(u32, nr) +#define BIT_U64(nr) BIT_TYPE(u64, nr) + #else /* defined(__ASSEMBLY__) */ /* -- cgit v1.2.3