From patchwork Tue Jul 4 14:10:33 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Weimer X-Patchwork-Id: 21403 Received: (qmail 31285 invoked by alias); 4 Jul 2017 14:10:40 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 30544 invoked by uid 89); 4 Jul 2017 14:10:40 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-26.9 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, RP_MATCHES_RCVD, SPF_HELO_PASS autolearn=ham version=3.3.2 spammy= X-HELO: mx1.redhat.com DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 8147A4E4D3 Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=fweimer@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 8147A4E4D3 From: Florian Weimer Subject: Re: [PATCH] assert: Suppress pedantic warning caused by statement expression [BZ# 21242] To: GNU C Library References: <6619e7e2-248e-08bc-6dc5-7b4d11bea3df@auburn.edu> <925e8a81-86f9-78a6-1578-660c04e39e3c@redhat.com> Message-ID: Date: Tue, 4 Jul 2017 16:10:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: On 07/04/2017 04:00 PM, Florian Weimer wrote: > On 06/26/2017 12:56 PM, Joseph Myers wrote: >> On Sun, 25 Jun 2017, Florian Weimer wrote: >> >>> I think we can use __extension__ if we also expand the expression >>> without __extension__ in an unevaluated context. The tricky part is to >>> find one that is independent of GNU extensions. >>> Perhaps this would work? >>> >>> # define assert(expr) \ >>> ((void) sizeof ((expr) == 0), __extension__ ({ \ >>> if (expr) \ >>> ; /* empty */ \ >>> else \ >>> __assert_fail (#expr, __FILE__, __LINE__, __FUNCTION__); \ >>> })) >>> >>> sizeof suppresses the evaluation of the first occurrence of expr. The >>> comparison is needed because sizeof cannot be applied to function >>> pointers and bitfields. C11 says that expr is compared to zero, so the >>> (expr) == 0 expression is well-formed. >>> >>> What do you think? Should we make this change? >> >> I think that's reasonable (appropriately commented to explain why it's >> done that way). > > This is what I came up with as a patch. > > I would consider this still appropriate during the freeze. It's > something we'd backport to glibc 2.25, too. Hopefully now with attachment. Florian assert: Suppress pedantic warning caused by statement expression 2017-07-04 Florian Weimer [BZ #21242] * assert/assert.h [__GNUC__ && !__STRICT_ANSI__] (assert): Suppress pedantic warning resulting from statement expression. (__ASSERT_FUNCTION): Add missing __extendsion__. diff --git a/assert/assert.h b/assert/assert.h index 22f0195..0ded8c7 100644 --- a/assert/assert.h +++ b/assert/assert.h @@ -91,13 +91,18 @@ __END_DECLS ? __ASSERT_VOID_CAST (0) \ : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION)) # else +/* The first occurrence of EXPR is not evaluated due to the sizeof, + but will trigger any pedantic warnings masked by the __extension__ + for the second occurrence. The explicit comparison against zero is + required to support function pointers and bit fields in this + context. */ # define assert(expr) \ - ({ \ + ((void) sizeof ((expr) == 0), __extension__ ({ \ if (expr) \ ; /* empty */ \ else \ __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION); \ - }) + })) # endif # ifdef __USE_GNU @@ -113,7 +118,7 @@ __END_DECLS C9x has a similar variable called __func__, but prefer the GCC one since it demangles C++ function names. */ # if defined __cplusplus ? __GNUC_PREREQ (2, 6) : __GNUC_PREREQ (2, 4) -# define __ASSERT_FUNCTION __PRETTY_FUNCTION__ +# define __ASSERT_FUNCTION __extension__ __PRETTY_FUNCTION__ # else # if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L # define __ASSERT_FUNCTION __func__