From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754019AbbFSILC (ORCPT ); Fri, 19 Jun 2015 04:11:02 -0400 Received: from mail-wg0-f52.google.com ([74.125.82.52]:35213 "EHLO mail-wg0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753356AbbFSIKt (ORCPT ); Fri, 19 Jun 2015 04:10:49 -0400 Date: Fri, 19 Jun 2015 10:10:44 +0200 From: Ingo Molnar To: Borislav Petkov Cc: LKML , Thomas Gleixner , "H. Peter Anvin" , Linus Torvalds Subject: Re: [PATCH] x86/head_32: Fix overflow warning with 32-bit binutils Message-ID: <20150619081044.GA32169@gmail.com> References: <1434700295-17721-1-git-send-email-bp@alien8.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1434700295-17721-1-git-send-email-bp@alien8.de> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Borislav Petkov wrote: > From: Borislav Petkov > > When building the kernel with 32-bit binutils built with support only > for the i386 target, we get the following warning: > > arch/x86/kernel/head_32.S:66: Warning: shift count out of range (32 is not between 0 and 31) > > The problem is that in that case, binutils' internal type representation > is 32-bit wide and the shift range overflows. > > In order to fix this, manipulate the shift expression which creates the > 4GiB constant to not overflow the shift count. > > Reported-and-tested-by: Enrico Mioso > Suggested-by: Michael Matz > Signed-off-by: Borislav Petkov > --- > arch/x86/kernel/head_32.S | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S > index 53eeb226657c..c601d1de5ae5 100644 > --- a/arch/x86/kernel/head_32.S > +++ b/arch/x86/kernel/head_32.S > @@ -63,8 +63,8 @@ > #endif > > /* Number of possible pages in the lowmem region */ > -LOWMEM_PAGES = (((1<<32) - __PAGE_OFFSET) >> PAGE_SHIFT) > - > +LOWMEM_PAGES = (((2<<31) - __PAGE_OFFSET) >> PAGE_SHIFT) > + Hm, so if internally GAS uses 64-bit types, couldn't we 'make sure' it's a 64-bit type, by using something like 31LL? Assuming GAS understands that? Or if the internal representation is 32 bits, then 2<<31 is just a fancy way of saying '0', right? So this could be written as: LOWMEM_PAGES = (-__PAGE_OFFSET >> PAGE_SHIFT) or: LOWMEM_PAGES = ((0 - __PAGE_OFFSET) >> PAGE_SHIFT) right? Or did it get it all wrong? Thanks, Ingo