From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56394) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZhhJc-0008CD-CX for qemu-devel@nongnu.org; Thu, 01 Oct 2015 13:06:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZhhJY-0004eN-BV for qemu-devel@nongnu.org; Thu, 01 Oct 2015 13:06:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39753) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZhhJY-0004e4-0d for qemu-devel@nongnu.org; Thu, 01 Oct 2015 13:06:40 -0400 Date: Thu, 1 Oct 2015 14:06:36 -0300 From: Eduardo Habkost Message-ID: <20151001170636.GD1260@thinpad.lan.raisama.net> References: <1443558863-26132-1-git-send-email-ehabkost@redhat.com> <1443558863-26132-3-git-send-email-ehabkost@redhat.com> <560C8DF8.7020700@twiddle.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <560C8DF8.7020700@twiddle.net> Subject: Re: [Qemu-devel] [PATCH 2/2] target-i386: Don't left shift negative constant List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Richard Henderson Cc: Paolo Bonzini , qemu-devel@nongnu.org On Thu, Oct 01, 2015 at 11:35:52AM +1000, Richard Henderson wrote: > On 09/30/2015 06:34 AM, Eduardo Habkost wrote: > >Left shift of negative values is undefined behavior. Detected by clang: > > qemu/target-i386/translate.c:2423:26: runtime error: > > left shift of negative value -8 > > > >This changes the code to reverse the sign after the left shift. > > > >Signed-off-by: Eduardo Habkost > >--- > > target-i386/translate.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > >diff --git a/target-i386/translate.c b/target-i386/translate.c > >index 8b35de1..cc59b7e 100644 > >--- a/target-i386/translate.c > >+++ b/target-i386/translate.c > >@@ -2420,7 +2420,7 @@ static void gen_pusha(DisasContext *s) > > { > > int i; > > gen_op_movl_A0_reg(R_ESP); > >- gen_op_addl_A0_im(-8 << s->dflag); > >+ gen_op_addl_A0_im(-(8 << s->dflag)); > > Better as -8U << s->d_flag? That's even more confusing to me. I wouldn't want to require other people to read the C specification to find out how many type conversions are happening in that statement. (Because I will have to do that, to find out what's the type of "-8U"). I would prefer an expression that doesn't involve any type conversion. But you are more familiar with that code, so it's up to you. -- Eduardo