From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Wang, Zhihong" <zhihong.wang@intel.com>
Subject: Re: [PATCH 1/3] eal/x86: fix build with clang for old AVX
Date: Thu, 4 Feb 2016 03:35:53 +0000
Message-ID: <8F6C2BD409508844A0EFC19955BE0941033ACABA@SHSMSX103.ccr.corp.intel.com>
References: <1454525799-25552-1-git-send-email-thomas.monjalon@6wind.com>
 <1454525799-25552-2-git-send-email-thomas.monjalon@6wind.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
To: Thomas Monjalon <thomas.monjalon@6wind.com>, "dev@dpdk.org" <dev@dpdk.org>
Return-path: <dev-bounces@dpdk.org>
Received: from mga09.intel.com (mga09.intel.com [134.134.136.24])
 by dpdk.org (Postfix) with ESMTP id 5A7DC8D90
 for <dev@dpdk.org>; Thu,  4 Feb 2016 04:35:56 +0100 (CET)
In-Reply-To: <1454525799-25552-2-git-send-email-thomas.monjalon@6wind.com>
Content-Language: en-US
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>

> Subject: [PATCH 1/3] eal/x86: fix build with clang for old AVX
>=20
> When configuring RTE_MACHINE to "default", rte_memcpy implementation
> is the default one (old AVX).
> In this code, clang raises a warning thanks to -Wsometimes-uninitialized:
>=20
> rte_memcpy.h:838:6: error:
> variable 'srcofs' is used uninitialized whenever 'if' condition is false
>         if (dstofss > 0) {
>             ^~~~~~~~~~~
> rte_memcpy.h:849:6: note: uninitialized use occurs here
>         if (srcofs =3D=3D 0) {
>             ^~~~~~
>=20
> It is fixed by initializing srcofs to 0.
>=20
> Fixes: 1ae817f9f887 ("eal/x86: tune memcpy for platforms without AVX512")
>=20
> Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>
> ---
>  lib/librte_eal/common/include/arch/x86/rte_memcpy.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)


Hi Thomas,

Thanks for pointing this out!
My last hasty modification on this is not correct.

The patch below will fix it. All modifications are tested.
Sorry for all the hassle! :'(

"srcofs" should be calculated based on source address anyway.


--- a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
+++ b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
@@ -512,8 +512,9 @@ COPY_BLOCK_64_BACK31:
 	/**
 	 * Make store aligned when copy size exceeds 512 bytes
 	 */
-	dstofss =3D 32 - ((uintptr_t)dst & 0x1F);
+	dstofss =3D (uintptr_t)dst & 0x1F;
 	if (dstofss > 0) {
+		dstofss =3D 32 - dstofss;
 		n -=3D dstofss;
 		rte_mov32((uint8_t *)dst, (const uint8_t *)src);
 		src =3D (const uint8_t *)src + dstofss;
@@ -834,14 +835,15 @@ COPY_BLOCK_64_BACK15:
 	 * unaligned copy functions require up to 15 bytes
 	 * backwards access.
 	 */
-	dstofss =3D 16 - ((uintptr_t)dst & 0x0F) + 16;
+	dstofss =3D (uintptr_t)dst & 0x0F;
 	if (dstofss > 0) {
+		dstofss =3D 16 - dstofss + 16;
 		n -=3D dstofss;
 		rte_mov32((uint8_t *)dst, (const uint8_t *)src);
 		src =3D (const uint8_t *)src + dstofss;
 		dst =3D (uint8_t *)dst + dstofss;
-		srcofs =3D ((uintptr_t)src & 0x0F);
 	}
+	srcofs =3D ((uintptr_t)src & 0x0F);
=20
 	/**
 	 * For aligned copy