Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754565AbaGKXq2 (ORCPT ); Fri, 11 Jul 2014 19:46:28 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:30141 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751221AbaGKXq1 (ORCPT ); Fri, 11 Jul 2014 19:46:27 -0400 Date: Sat, 12 Jul 2014 01:45:48 +0200 From: Daniel Kiper To: Boris Ostrovsky Cc: linux-kernel@vger.kernel.org, x86@kernel.org, xen-devel@lists.xenproject.org, andrew.cooper3@citrix.com, david.vrabel@citrix.com, hpa@zytor.com, ian.campbell@citrix.com, jbeulich@suse.com, jeremy@goop.org, konrad.wilk@oracle.com, matt.fleming@intel.com, mingo@redhat.com, stefano.stabellini@eu.citrix.com, tglx@linutronix.de Subject: Re: [PATCH 2/2] arch/x86/xen: Silence compiler warnings Message-ID: <20140711234548.GM13620@olila.local.net-space.pl> References: <1405108461-3223-1-git-send-email-daniel.kiper@oracle.com> <1405108461-3223-3-git-send-email-daniel.kiper@oracle.com> <53C04322.1050000@oracle.com> <20140711201050.GJ13620@olila.local.net-space.pl> <53C049DB.3050904@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <53C049DB.3050904@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 11, 2014 at 04:32:27PM -0400, Boris Ostrovsky wrote: > On 07/11/2014 04:10 PM, Daniel Kiper wrote: > >On Fri, Jul 11, 2014 at 04:03:46PM -0400, Boris Ostrovsky wrote: > >>On 07/11/2014 03:54 PM, Daniel Kiper wrote: > >>>Compiler complains in the following way when x86 32-bit kernel > >>>with Xen support is build: > >>> > >>> CC arch/x86/xen/enlighten.o > >>>arch/x86/xen/enlighten.c: In function ‘xen_start_kernel’: > >>>arch/x86/xen/enlighten.c:1726:3: warning: right shift count >= width of type [enabled by default] > >>> > >>>Such line contains following EFI initialization code: > >>> > >>>boot_params.efi_info.efi_systab_hi = (__u32)(__pa(efi_systab_xen) >> 32); > >>> > >>>There is no issue if x86 64-bit kernel is build. However, 32-bit case > >>>generate warning (even if that code will not be executed because Xen > >>>does not work on 32-bit EFI platforms) due to __pa() returning unsigned long > >>>type which has 32-bits width. So move whole EFI initialization stuff > >>>to separate function and build its body conditionally to avoid above > >>>mentioned warning on x86 32-bit architecture. > >>> > >>>Signed-off-by: Daniel Kiper > >>>--- > >>> arch/x86/xen/enlighten.c | 35 ++++++++++++++++++++++------------- > >>> 1 file changed, 22 insertions(+), 13 deletions(-) > >>> > >>>diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c > >>>index bc89647..6abec74 100644 > >>>--- a/arch/x86/xen/enlighten.c > >>>+++ b/arch/x86/xen/enlighten.c > >>>@@ -1516,12 +1516,32 @@ static void __init xen_pvh_early_guest_init(void) > >>> #endif > >>> } > >>>+static void __init xen_efi_init(void) > >>>+{ > >>>+#ifdef CONFIG_XEN_EFI > >>>+ efi_system_table_t *efi_systab_xen; > >>>+ > >>>+ efi_systab_xen = xen_efi_probe(); > >>>+ > >>>+ if (efi_systab_xen == NULL) > >>>+ return; > >>>+ > >>>+ strncpy((char *)&boot_params.efi_info.efi_loader_signature, "Xen", > >>>+ sizeof(boot_params.efi_info.efi_loader_signature)); > >>>+ boot_params.efi_info.efi_systab = (__u32)__pa(efi_systab_xen); > >>>+ boot_params.efi_info.efi_systab_hi = (__u32)(__pa(efi_systab_xen) >> 32); > >>>+ > >>>+ set_bit(EFI_BOOT, &efi.flags); > >>>+ set_bit(EFI_PARAVIRT, &efi.flags); > >>>+ set_bit(EFI_64BIT, &efi.flags); > >>>+#endif > >>>+} > >>>+ > >>> /* First C function to be called on Xen boot */ > >>> asmlinkage __visible void __init xen_start_kernel(void) > >>> { > >>> struct physdev_set_iopl set_iopl; > >>> int rc; > >>>- efi_system_table_t *efi_systab_xen; > >>> if (!xen_start_info) > >>> return; > >>>@@ -1717,18 +1737,7 @@ asmlinkage __visible void __init xen_start_kernel(void) > >>> xen_setup_runstate_info(0); > >>>- efi_systab_xen = xen_efi_probe(); > >>>- > >>>- if (efi_systab_xen) { > >>>- strncpy((char *)&boot_params.efi_info.efi_loader_signature, "Xen", > >>>- sizeof(boot_params.efi_info.efi_loader_signature)); > >>>- boot_params.efi_info.efi_systab = (__u32)__pa(efi_systab_xen); > >>>- boot_params.efi_info.efi_systab_hi = (__u32)(__pa(efi_systab_xen) >> 32); > >>>- > >>>- set_bit(EFI_BOOT, &efi.flags); > >>>- set_bit(EFI_PARAVIRT, &efi.flags); > >>>- set_bit(EFI_64BIT, &efi.flags); > >>>- } > >>>+ xen_efi_init(); > >>I'd put ifdef CONFIG_XEN_EFI around the call instead of having it > >>inside the routine. > >Well, I thought about that a bit and I prefer function like Konrad. > >Could you agree with him which solution do you (as maintainers) prefer? > > > > I am not arguing against having a separate routine. All I am saying > is that calling xen_efi_init() when CONFIG_XEN_EFI is not defined > doesn't look logical. It will also add an unnecessary call (although Ahh... I misunderstood you. However, your proposal, as below: #ifdef CONFIG_XEN_EFI xen_efi_init(); #endif does not solve the problem because this vulnerable shift will be still visible for compiler during x86 32-bit kernel build. > compiler may optimize it out). Please loot at arch/x86/xen/enlighten.c:xen_check_mwait() and arch/x86/xen/enlighten.c:xen_boot_params_init_edd() (probably there are more stuff like that around). As I can see this is fairly common solution and probably compiler cope with it quite well. Have a nice weekend, Daniel -- 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/