Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933206AbXLQBs0 (ORCPT ); Sun, 16 Dec 2007 20:48:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760953AbXLQBsT (ORCPT ); Sun, 16 Dec 2007 20:48:19 -0500 Received: from pip15.gyao.ne.jp ([61.122.117.253]:26723 "EHLO mx.gate01.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1760352AbXLQBsS (ORCPT ); Sun, 16 Dec 2007 20:48:18 -0500 Date: Mon, 17 Dec 2007 10:48:05 +0900 From: Paul Mundt To: Andrew Morton Cc: linux-kernel@vger.kernel.org Subject: div64: Rework 64-bit type safety checks in do_div(). Message-ID: <20071217014805.GA15156@linux-sh.org> Mail-Followup-To: Paul Mundt , Andrew Morton , linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2523 Lines: 69 The current do_div() implementation has a bogus pointer compare to generate build warnings on mismatch on 32-bit, unfortunately this not only triggers for size mismatch, but also _any_ type mismatch, even on reasonable 64-bit values: In file included from kernel/sched.c:869: kernel/sched_debug.c: In function 'nsec_high': kernel/sched_debug.c:38: warning: comparison of distinct pointer types lacks a cast kernel/sched_debug.c:41: warning: comparison of distinct pointer types lacks a cast kernel/sched_debug.c: In function 'nsec_low': kernel/sched_debug.c:51: warning: comparison of distinct pointer types lacks a cast ... The options are to either 'fix' all callers of do_div() to make sure they're using a uint64_t explicitly, or to update do_div() to make sure that the value is 64-bits, regardless of specific type. Currently everything that uses the generic do_div() causes a warning when using one of 'u64', 'long long', etc. instead of 'uint64_t'. Half-assed empirical testing indicates that the number of false positives far outweighs any benefits of this type of checking: $ git grep uint64_t | wc -l 947 $ git grep u64 | wc -l 13942 In short, screw uint64_t and its fan club. Signed-off-by: Paul Mundt --- include/asm-generic/div64.h | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h index a4a4937..63e7768 100644 --- a/include/asm-generic/div64.h +++ b/include/asm-generic/div64.h @@ -19,6 +19,7 @@ #include #include +#include #if BITS_PER_LONG == 64 @@ -39,13 +40,11 @@ static inline uint64_t div64_64(uint64_t dividend, uint64_t divisor) extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor); -/* The unnecessary pointer compare is there - * to check for type safety (n must be 64bit) - */ +/* The BUILD_BUG_ON() is there to check for type safety (n must be 64bit) */ # define do_div(n,base) ({ \ uint32_t __base = (base); \ uint32_t __rem; \ - (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \ + BUILD_BUG_ON(sizeof(n) != sizeof(uint64_t)); \ if (likely(((n) >> 32) == 0)) { \ __rem = (uint32_t)(n) % __base; \ (n) = (uint32_t)(n) / __base; \ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/