From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50040) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZhZF6-00051z-P6 for qemu-devel@nongnu.org; Thu, 01 Oct 2015 04:29:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZhZF1-0005AF-Ts for qemu-devel@nongnu.org; Thu, 01 Oct 2015 04:29:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37497) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZhZF1-0005AB-OL for qemu-devel@nongnu.org; Thu, 01 Oct 2015 04:29:27 -0400 References: <1443558863-26132-1-git-send-email-ehabkost@redhat.com> <1443558863-26132-2-git-send-email-ehabkost@redhat.com> <560BE355.60901@redhat.com> <560C44F4.6030200@twiddle.net> From: Paolo Bonzini Message-ID: <560CEEE4.6080505@redhat.com> Date: Thu, 1 Oct 2015 10:29:24 +0200 MIME-Version: 1.0 In-Reply-To: <560C44F4.6030200@twiddle.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/2] target-i386: Use 1UL for bit shift List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Richard Henderson , Eduardo Habkost , qemu-devel@nongnu.org On 30/09/2015 22:24, Richard Henderson wrote: > On 09/30/2015 11:27 PM, Paolo Bonzini wrote: >> >> >> On 29/09/2015 22:34, Eduardo Habkost wrote: >>> Fix undefined behavior detected by clang runtime check: >>> >>> qemu/target-i386/cpu.c:1494:15: runtime error: >>> left shift of 1 by 31 places cannot be represented in type 'int' >>> >>> While doing that, add extra parenthesis for clarity. >>> >>> Reported-by: Peter Maydell >>> Signed-off-by: Eduardo Habkost >>> --- >>> target-i386/cpu.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/target-i386/cpu.c b/target-i386/cpu.c >>> index 2b914b2..6af6db9 100644 >>> --- a/target-i386/cpu.c >>> +++ b/target-i386/cpu.c >>> @@ -1491,7 +1491,7 @@ static void >>> report_unavailable_features(FeatureWord w, uint32_t mask) >>> int i; >>> >>> for (i = 0; i < 32; ++i) { >>> - if (1 << i & mask) { >>> + if ((1UL << i) & mask) { >> >> 1U is enough. >> >> Paolo >> >> ps: Ego ceterum censeo that these warnings are useless and uglify the >> code unnecessarily. But it looks like I'm in a minority so the patch is >> okay. > > I totally agree. There are no ones-compliment machines anymore, and so > the whole point of that "undefined" in the C standard is moot. Let's > all accept that shifts of signed quantities do exactly what we expect. > > Without looking, I don't suppose either compiler has a switch to disable > just the shift part of ubsan? Nope, I already asked. :) Paolo