From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752421AbdBUPcK (ORCPT <rfc822;w@1wt.eu>);
        Tue, 21 Feb 2017 10:32:10 -0500
Received: from smtp.transmode.se ([31.15.61.139]:56381 "EHLO smtp.transmode.se"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752219AbdBUPcD (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 21 Feb 2017 10:32:03 -0500
X-Greylist: delayed 470 seconds by postgrey-1.27 at vger.kernel.org; Tue, 21 Feb 2017 10:32:02 EST
From: Joakim Tjernlund <joakim.tjernlund@infinera.com>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Joakim Tjernlund <joakim.tjernlund@infinera.com>
Subject: [PATCH 2/2] compiler.h: fix C++ uninitialized const issue
Date: Tue, 21 Feb 2017 16:24:05 +0100
Message-Id: <20170221152405.7552-2-joakim.tjernlund@infinera.com>
X-Mailer: git-send-email 2.10.2
In-Reply-To: <20170221152405.7552-1-joakim.tjernlund@infinera.com>
References: <20170221152405.7552-1-joakim.tjernlund@infinera.com>
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

C++ does not like the union { typeof(x) __val; char __c[1]; } __u
construct for const types:
 error: uninitialized const member in
 'union atomic_read(const atomic_t*)::<anonymous>'
Address this by creating a C++ version of READ_ONCE where this union is
initialized: union { void _u(){}; typeof(x) __val; char __c[1]; } __u={0}

To please gcc 6.3.0 also add in a _u(){} as default ctor.

This makes C++ happy enough to build.

Signed-off-by: Joakim Tjernlund <joakim.tjernlund@infinera.com>
---
 include/linux/compiler.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index cf0fa5d..0a047fd 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -300,6 +300,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  * required ordering.
  */
 
+#ifndef __cplusplus
 #define __READ_ONCE(x, check)						\
 ({									\
 	union { typeof(x) __val; char __c[1]; } __u;			\
@@ -309,6 +310,17 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
 	__u.__val;							\
 })
+#else
+#define __READ_ONCE(x, check)						\
+({									\
+	union { void _u(){}; typeof(x) __val; char __c[1]; } __u={0};	\
+	if (check)							\
+		__read_once_size(&(x), __u.__c, sizeof(x));		\
+	else								\
+		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
+	__u.__val;							\
+})
+#endif
 #define READ_ONCE(x) __READ_ONCE(x, 1)
 
 /*
-- 
2.10.2