Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751191AbaLOMzM (ORCPT ); Mon, 15 Dec 2014 07:55:12 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50335 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750723AbaLOMzH (ORCPT ); Mon, 15 Dec 2014 07:55:07 -0500 Date: Mon, 15 Dec 2014 14:54:26 +0200 From: "Michael S. Tsirkin" To: Russell King - ARM Linux Cc: Will Deacon , "linux-arch@vger.kernel.org" , Arnd Bergmann , Catalin Marinas , "linux-kernel@vger.kernel.org" , Christopher Covington , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 03/18] arm64/uaccess: fix sparse errors Message-ID: <20141215125426.GA27583@redhat.com> References: <1418575877-21488-1-git-send-email-mst@redhat.com> <1418575877-21488-4-git-send-email-mst@redhat.com> <20141215111716.GG20738@arm.com> <20141215112310.GG11285@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141215112310.GG11285@n2100.arm.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 15, 2014 at 11:23:11AM +0000, Russell King - ARM Linux wrote: > On Mon, Dec 15, 2014 at 11:17:16AM +0000, Will Deacon wrote: > > On Sun, Dec 14, 2014 at 04:52:09PM +0000, Michael S. Tsirkin wrote: > > > virtio wants to read bitwise types from userspace using get_user. At the > > > moment this triggers sparse errors, since the value is passed through an > > > integer. > > > > > > Fix that up using __force. > > > > > > Signed-off-by: Michael S. Tsirkin > > > --- > > > arch/arm64/include/asm/uaccess.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > > > index 3bf8f4e..8d66bcf 100644 > > > --- a/arch/arm64/include/asm/uaccess.h > > > +++ b/arch/arm64/include/asm/uaccess.h > > > @@ -147,7 +147,7 @@ do { \ > > > default: \ > > > BUILD_BUG(); \ > > > } \ > > > - (x) = (__typeof__(*(ptr)))__gu_val; \ > > > + (x) = (__force __typeof__(*(ptr)))__gu_val; \ > > > } while (0) > > > > > > #define __get_user(x, ptr) \ > > > > Acked-by: Will Deacon > > This also means you can do stuff like: > > u32 *p; > __le32 v; > > err = get_user(p, v); > > which is not right. Both the dereferenced pointer type and the destination > type should be compatible, and if one is a bitwise type but the other isn't, > that seems like a valid case to warn. I just verified this case: #define __force __attribute__((force)) #define __bitwise__ __attribute__((bitwise)) #define get_user(x, ptr) \ do {\ unsigned long __gu_val = 0; \ (x) = (__force __typeof__(*(ptr)))__gu_val; \ } while (0) typedef unsigned u32; typedef u32 __bitwise__ __le32; static u32 *p; static __le32 v; int main(int argc, char **argv) { get_user(v, p); return 0; } Produces a warning as expected. So I think the above comment is a result of a mistake. Can you confirm please? > I don't see any use of get_user() in drivers/virtio in mainline, so I can't > check further. this is an example of the case which I'm fixing: #define __force __attribute__((force)) #define __bitwise__ __attribute__((bitwise)) #define get_user(x, ptr) \ do {\ unsigned long __gu_val = 0; \ (x) = (__typeof__(*(ptr)))__gu_val; \ } while (0) typedef unsigned u32; typedef u32 __bitwise__ __le32; static __le32 *p; static __le32 v; int main(int argc, char **argv) { get_user(v, p); return 0; } the code is correct but produces a warning: a.c:18:9: warning: cast to restricted __le32 The cast near __typeof__ above needs __force, this is what my patch does. > -- > FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up > according to speedtest.net. -- 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/