From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753748AbYATJwe (ORCPT ); Sun, 20 Jan 2008 04:52:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753462AbYATJwY (ORCPT ); Sun, 20 Jan 2008 04:52:24 -0500 Received: from ozlabs.org ([203.10.76.45]:60774 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751841AbYATJwX (ORCPT ); Sun, 20 Jan 2008 04:52:23 -0500 From: Rusty Russell To: Linus Torvalds Subject: [PATCH 4/6] typesafe: cast_if_type to allow macros functions which take more than one type. Date: Sun, 20 Jan 2008 20:51:42 +1100 User-Agent: KMail/1.9.6 (enterprise 0.20070907.709405) Cc: Andrew Morton , linux-kernel@vger.kernel.org, Jeff Garzik , Tejun Heo References: <200801202046.14746.rusty@rustcorp.com.au> <200801202048.34796.rusty@rustcorp.com.au> <200801202050.41495.rusty@rustcorp.com.au> In-Reply-To: <200801202050.41495.rusty@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200801202051.42958.rusty@rustcorp.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Signed-off-by: Rusty Russell diff -r e6626cc7bdc2 include/linux/compiler-gcc.h --- a/include/linux/compiler-gcc.h Sun Jan 20 18:51:51 2008 +1100 +++ b/include/linux/compiler-gcc.h Sun Jan 20 18:57:14 2008 +1100 @@ -53,3 +53,20 @@ #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. */ +#define cast_if_type(expr, oktype, desttype) \ + __builtin_choose_expr(__builtin_types_compatible_p(typeof(1?(expr):NULL), \ + oktype), \ + (desttype)(expr), (expr)) diff -r e6626cc7bdc2 include/linux/compiler-intel.h --- a/include/linux/compiler-intel.h Sun Jan 20 18:51:51 2008 +1100 +++ b/include/linux/compiler-intel.h Sun Jan 20 18:57:14 2008 +1100 @@ -29,3 +29,5 @@ #endif #define uninitialized_var(x) x + +#define cast_if_type(expr, oktype, desttype) ((desttype)(expr))