documentation: update CodingStyle on local variables naming in macros

[linux-2.6-microblaze.git] / Documentation / CodingStyle

diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
index 449a8a1..4d4f06d 100644 (file)
--- a/Documentation/CodingStyle
+++ b/Documentation/CodingStyle
@@ -659,6 +659,19 @@ macros using parameters.
 #define CONSTANT 0x4000
 #define CONSTEXP (CONSTANT | 3)
 
+5) namespace collisions when defining local variables in macros resembling
+functions:
+
+#define FOO(x)                         \
+({                                     \
+       typeof(x) ret;                  \
+       ret = calc_ret(x);              \
+       (ret);                          \
+)}
+
+ret is a common name for a local variable - __foo_ret is less likely
+to collide with an existing variable.
+
 The cpp manual deals with macros exhaustively. The gcc internals manual also
 covers RTL which is used frequently with assembly language in the kernel.