cast_if_type: allow macros functions which take more than one type. To create functions which can take two types, but still warn on any other types, we need a way of casting one type and no others. To make things more complex, it should correctly handle function args, NULL, and be usable in initializers. __builtin_choose_expr was introduced in gcc 3.1 (kernel needs >= 3.2 anyway). Signed-off-by: Rusty Russell --- include/linux/compiler-gcc.h | 19 +++++++++++++++++++ include/linux/compiler-intel.h | 2 ++ 2 files changed, 21 insertions(+) diff -r bde8a949d956 include/linux/compiler-gcc.h --- a/include/linux/compiler-gcc.h Mon Apr 07 15:27:30 2008 +1000 +++ b/include/linux/compiler-gcc.h Mon Apr 07 16:19:49 2008 +1000 @@ -53,3 +53,22 @@ #define noinline __attribute__((noinline)) #define __attribute_const__ __attribute__((__const__)) #define __maybe_unused __attribute__((unused)) + +/** + * cast_if_type - allow an alternate type + * @expr: the expression to optionally cast + * @oktype: the type to allow. + * @desttype: the type to cast to. + * + * This is used to accept a particular alternate type for an expression: + * because any other types will not be cast, they will cause a warning as + * normal. + * + * Note that the unnecessary trinary forces functions to devolve into + * function pointers as users expect, but means @expr must be a pointer or + * integer. + */ +#define cast_if_type(expr, oktype, desttype) \ + __builtin_choose_expr(__builtin_types_compatible_p(typeof(1?(expr):0),\ + oktype), \ + (desttype)(expr), (expr)) diff -r bde8a949d956 include/linux/compiler-intel.h --- a/include/linux/compiler-intel.h Mon Apr 07 15:27:30 2008 +1000 +++ b/include/linux/compiler-intel.h Mon Apr 07 16:19:49 2008 +1000 @@ -29,3 +29,5 @@ #endif #define uninitialized_var(x) x + +#define cast_if_type(expr, oktype, desttype) ((desttype)(expr))