Messages in this thread Patch in this message | | | From | Rusty Russell <> | Subject | [PATCH 1/4] typesafe: cast_if_type: allow macros functions which take more than one type. | Date | Fri, 25 Jul 2008 12:14:51 +1000 |
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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).
(includes Harvey Harrison <harvey.harrison@gmail.com>'s sparse fix)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Harvey Harrison <harvey.harrison@gmail.com> --- include/linux/compiler-gcc.h | 18 ++++++++++++++++++ include/linux/compiler-intel.h | 2 ++ 2 files changed, 20 insertions(+)
diff -r ecbc022961d8 include/linux/compiler-gcc.h --- a/include/linux/compiler-gcc.h Mon Jul 14 12:30:35 2008 +1000 +++ b/include/linux/compiler-gcc.h Mon Jul 14 20:46:23 2008 +1000 @@ -61,3 +61,21 @@ #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):(expr)), oktype), \ + (desttype)(expr), (expr)) diff -r ecbc022961d8 include/linux/compiler-intel.h --- a/include/linux/compiler-intel.h Mon Jul 14 12:30:35 2008 +1000 +++ b/include/linux/compiler-intel.h Mon Jul 14 20:46:23 2008 +1000 @@ -29,3 +29,5 @@ #endif #define uninitialized_var(x) x + +#define cast_if_type(expr, oktype, desttype) ((desttype)(expr))
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