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 <mwi...@suse.com>
---
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
