From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33675) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fGmgB-0005PY-BF for qemu-devel@nongnu.org; Thu, 10 May 2018 10:36:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fGmgA-00082b-Io for qemu-devel@nongnu.org; Thu, 10 May 2018 10:36:23 -0400 Received: from orth.archaic.org.uk ([2001:8b0:1d0::2]:41582) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fGmgA-00080D-Bf for qemu-devel@nongnu.org; Thu, 10 May 2018 10:36:22 -0400 From: Peter Maydell Date: Thu, 10 May 2018 15:36:18 +0100 Message-Id: <20180510143618.23673-1-peter.maydell@linaro.org> Subject: [Qemu-devel] [PATCH] atomic.h: Work around gcc spurious "unused value" warning List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: patches@linaro.org, Richard Henderson , Paolo Bonzini Some versions of gcc produce a spurious warning if the result of __atomic_compare_echange_n() is not used and the type involved is a signed 8 bit value: error: value computed is not used [-Werror=unused-value] This has been seen on at least gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609 Work around this by using an explicit cast to void to indicate that we don't care about the return value. We don't currently use our atomic_cmpxchg() macro on any signed 8 bit types, but the upcoming support for the Arm v8.1-Atomics will require it. Signed-off-by: Peter Maydell --- Sending out my workaround as an actual patch. If this is OK I'll put in via target-arm.next as it's a dependency for the v8.1-atomics series. include/qemu/atomic.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h index d73c9e14d7..9ed39effd3 100644 --- a/include/qemu/atomic.h +++ b/include/qemu/atomic.h @@ -187,7 +187,7 @@ /* Returns the eventual value, failed or not */ #define atomic_cmpxchg__nocheck(ptr, old, new) ({ \ typeof_strip_qual(*ptr) _old = (old); \ - __atomic_compare_exchange_n(ptr, &_old, new, false, \ + (void)__atomic_compare_exchange_n(ptr, &_old, new, false, \ __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \ _old; \ }) -- 2.17.0