documentation: update CodingStyle on local variables naming in macros

Describe proper naming convention for local variables in macros
resembling functions.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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)
 
 #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.
 
 The cpp manual deals with macros exhaustively. The gcc internals manual also
 covers RTL which is used frequently with assembly language in the kernel.