Add a description, an example and a possible workaround to the
MACRO_ARG_REUSE check.
Signed-off-by: Martin Fernandez <martin.fernandez@xxxxxxxxxxxxx>
Acked-by: Dwaipayan Ray <dwaipayanray1@xxxxxxxxx>
---
Documentation/dev-tools/checkpatch.rst | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index b52452bc2963..86545c65cf7b 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -759,6 +759,26 @@ Indentation and Line Breaks
Macros, Attributes and Symbols
------------------------------
+ **ARG_REUSE**
+ Using the same argument multiple times in the macro definition
+ would lead to unwanted side-effects.
+
+ For example, given a `min` macro defined like::
+
+ #define min(x, y) ((x) < (y) ? (x) : (y))
+
+ If you call it with `min(foo(x), 0)`, it would expand to::
+
+ foo(x) < 0 ? foo(x) : 0
+
+ If `foo` has side-effects or it's an expensive calculation the
+ results might not be what the user intended.
+
+ For a workaround the idea is to define local variables to hold the
+ macro's arguments. Checkout the actual implementation of `min` in
+ include/linux/minmax.h for the full implementation of the
+ workaround.
+
**ARRAY_SIZE**
The ARRAY_SIZE(foo) macro should be preferred over
sizeof(foo)/sizeof(foo[0]) for finding number of elements in an
--
2.30.2
