Sparse emits errors about ilog2() in array indices because of the use of __ilog2_32() and __ilog2_64(), rightly so (https://www.spinics.net/lists/linux-sparse/msg03471.html). Create a const_ilog2() variant that works with sparse for this scenario. (Note: checkpatch.pl complains about missing parentheses, but that appears to be a false positive. I can get rid of the warning simply by inserting whitespace, making checkpatch "see" the whole macro). Signed-off-by: Martin Wilck <mwilck@xxxxxxxx> --- include/linux/log2.h | 35 ++++++++++++++++++++++++----------- 1 file changed, 24 insertions(+), 11 deletions(-) diff --git a/include/linux/log2.h b/include/linux/log2.h index 41a1ae0..2af7f778 100644 --- a/include/linux/log2.h +++ b/include/linux/log2.h @@ -72,16 +72,13 @@ unsigned long __rounddown_pow_of_two(unsigned long n) } /** - * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value + * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value * @n: parameter * - * constant-capable log of base 2 calculation - * - this can be used to initialise global variables from constant data, hence - * the massive ternary operator construction - * - * selects the appropriately-sized optimised version depending on sizeof(n) + * Use this where sparse expects a true constant expression, e.g. for array + * indices. */ -#define ilog2(n) \ +#define const_ilog2(n) \ ( \ __builtin_constant_p(n) ? ( \ (n) < 2 ? 0 : \ @@ -147,10 +144,26 @@ unsigned long __rounddown_pow_of_two(unsigned long n) (n) & (1ULL << 4) ? 4 : \ (n) & (1ULL << 3) ? 3 : \ (n) & (1ULL << 2) ? 2 : \ - 1 ) : \ - (sizeof(n) <= 4) ? \ - __ilog2_u32(n) : \ - __ilog2_u64(n) \ + 1) : \ + -1) + +/** + * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value + * @n: parameter + * + * constant-capable log of base 2 calculation + * - this can be used to initialise global variables from constant data, hence + * the massive ternary operator construction + * + * selects the appropriately-sized optimised version depending on sizeof(n) + */ +#define ilog2(n) \ +( \ + __builtin_constant_p(n) ? \ + const_ilog2(n) : \ + (sizeof(n) <= 4) ? \ + __ilog2_u32(n) : \ + __ilog2_u64(n) \ ) /** -- 2.16.1
