From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id E2A373938C23; Fri, 1 May 2020 18:55:29 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org E2A373938C23 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1588359329; bh=f3Wy+xSzzpaM+zseaxV9ug5TEHoblTAvp5/5oh9ZH8I=; h=From:To:Subject:Date:In-Reply-To:References:From; b=eZGSDjjqSOX/VlWfbEwnIZidP8wkntstR5dgq1vR21tjm20rcWzPjp5fimsDqgcWh VpjbV/qheoiFDzrR5NaJ0GJ74XDYxR3k4AKgz1koLm1GJxVDaZc5V6ZKtKMLcT2jIb uEgiqFoX3QBiEDWJUtqiNQEoV0Mhtc2f0QzK+x44= From: "sbergman at redhat dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/92893] [10 Regression] Unhelpful -Wstringop-overflow warning for a trailing one-element array Date: Fri, 01 May 2020 18:55:29 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 10.0 X-Bugzilla-Keywords: diagnostic X-Bugzilla-Severity: normal X-Bugzilla-Who: sbergman at redhat dot com X-Bugzilla-Status: RESOLVED X-Bugzilla-Resolution: DUPLICATE X-Bugzilla-Priority: P2 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: 10.0 X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 01 May 2020 18:55:30 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D92893 --- Comment #9 from Stephan Bergmann --- (In reply to Martin Sebor from comment #2) > Defining Str like so works for the test case: >=20 > struct Str { > template Str(Cat c) > { > struct Flex { char c, a[]; } *p =3D (Flex*)get(); > c.add(p->a); > } > }; So I had created "Silence b= ogus -Wstringop-overflow with GCC trunk towards GCC 10" back in last December, a= nd it sufficed to suppress all those warnings when compiling LibreOffice with then-trunk GCC, with optimizations enabled. However, meanwhile GCC has cha= nged again so that at least one place in the LibreOffice code now produces two -Werror=3Dstringop-overflow=3D in one such struct Hack { char c; char a[]; }; workaround. (While in general the workarounds appear to still be effective= in suppressing other such warnings.) Bisecting, I found that first > commit ef29b12cfbb4979a89b3cbadbf485a77c8fd8fce > Author: Martin Sebor > Date: Sat Dec 14 00:52:46 2019 +0000 >=20 > PR middle-end/91582 - missing heap overflow detection for strcpy caused a new "writing 1 byte into a region of size 0" at > In file included from /home/user/libreoffice/include/rtl/string.hxx:41, > from /home/user/libreoffice/include/rtl/ustring.hxx:37, > from /home/user/libreoffice/include/unotest/filters-test= .hxx:14, > from /home/user/libreoffice/unotest/source/cpp/filters-t= est.cxx:14: > In member function =E2=80=98char* rtl::OStringConcat::addData(cha= r*) const [with T1 =3D rtl::OStringLiteral; T2 =3D const char [2]]=E2=80=99, > inlined from =E2=80=98char* rtl::OStringConcat::addData(char*= ) const [with T1 =3D rtl::OStringConcat; T2 =3D rtl::OString]=E2=80=99 at /home/user/libreoffice/include/rtl/stri= ngconcat.hxx:256:114, > inlined from =E2=80=98rtl::OString::OString(rtl::OStringConcat&&) [with T1 =3D rtl::OStringConcat; = T2 =3D rtl::OString]=E2=80=99 at /home/user/libreoffice/include/rtl/string.= hxx:281:34, > inlined from =E2=80=98void test::FiltersTest::recursiveScan(test::fil= terStatus, const rtl::OUString&, const rtl::OUString&, const rtl::OUString&= , SfxFilterFlags, SotClipboardFormatId, unsigned int, bool)=E2=80=99 at /ho= me/user/libreoffice/unotest/source/cpp/filters-test.cxx:111:67: > /home/user/libreoffice/include/rtl/stringconcat.hxx:77:11: error: writing= 1 byte into a region of size 0 [-Werror=3Dstringop-overflow=3D] > 77 | memcpy( buffer, data, length ); > | ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~ > In file included from /home/user/libreoffice/include/rtl/ustring.hxx:37, > from /home/user/libreoffice/include/unotest/filters-test= .hxx:14, > from /home/user/libreoffice/unotest/source/cpp/filters-t= est.cxx:14: > /home/user/libreoffice/include/rtl/string.hxx: In member function =E2=80= =98void test::FiltersTest::recursiveScan(test::filterStatus, const rtl::OUS= tring&, const rtl::OUString&, const rtl::OUString&, SfxFilterFlags, SotClip= boardFormatId, unsigned int, bool)=E2=80=99: > /home/user/libreoffice/include/rtl/string.hxx:280:32: note: at offset 0 t= o object =E2=80=98rtl::OString::OString(rtl::OStringConcat&&) [with= T1 =3D rtl::OStringConcat; T2 =3D rtl= ::OString]::Hack::c=E2=80=99 with size 1 declared here > 280 | struct Hack { char c; char a[]; }; > | ^ and later > commit a9a437ffc4269650e34af92c4fb095b7ed98f94a > Author: Jakub Jelinek > Date: Tue Mar 17 13:36:41 2020 +0100 >=20 > tree-ssa-strlen: Fix up count_nonzero_bytes* [PR94015] started to even cause an additional "writing 4 bytes into a region of size = 1" > In file included from /home/user/libreoffice/include/rtl/string.hxx:41, > from /home/user/libreoffice/include/rtl/ustring.hxx:37, > from /home/user/libreoffice/include/unotest/filters-test= .hxx:14, > from /home/user/libreoffice/unotest/source/cpp/filters-t= est.cxx:14: > In function =E2=80=98char* rtl::addDataHelper(char*, const char*, std::si= ze_t)=E2=80=99, > inlined from =E2=80=98static char* rtl::ToStringHelper::addData(char*, const rtl::OStringLiteral&)=E2=80=99 at /home/user/l= ibreoffice/include/rtl/string.hxx:1907:91, > inlined from =E2=80=98char* rtl::OStringConcat::addData(char*= ) const [with T1 =3D rtl::OStringLiteral; T2 =3D const char [2]]=E2=80=99 a= t /home/user/libreoffice/include/rtl/stringconcat.hxx:222:103, > inlined from =E2=80=98char* rtl::OStringConcat::addData(char*= ) const [with T1 =3D rtl::OStringConcat; T2 =3D rtl::OString]=E2=80=99 at /home/user/libreoffice/include/rtl/stri= ngconcat.hxx:256:114, > inlined from =E2=80=98rtl::OString::OString(rtl::OStringConcat&&) [with T1 =3D rtl::OStringConcat; = T2 =3D rtl::OString]=E2=80=99 at /home/user/libreoffice/include/rtl/string.= hxx:281:34, > inlined from =E2=80=98void test::FiltersTest::recursiveScan(test::fil= terStatus, const rtl::OUString&, const rtl::OUString&, const rtl::OUString&= , SfxFilterFlags, SotClipboardFormatId, unsigned int, bool)=E2=80=99 at /ho= me/user/libreoffice/unotest/source/cpp/filters-test.cxx:111:67: > /home/user/libreoffice/include/rtl/stringconcat.hxx:77:11: error: writing= 4 bytes into a region of size 1 [-Werror=3Dstringop-overflow=3D] > 77 | memcpy( buffer, data, length ); > | ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~ > In file included from /home/user/libreoffice/include/rtl/ustring.hxx:37, > from /home/user/libreoffice/include/unotest/filters-test= .hxx:14, > from /home/user/libreoffice/unotest/source/cpp/filters-t= est.cxx:14: > /home/user/libreoffice/include/rtl/string.hxx: In member function =E2=80= =98void test::FiltersTest::recursiveScan(test::filterStatus, const rtl::OUS= tring&, const rtl::OUString&, const rtl::OUString&, SfxFilterFlags, SotClip= boardFormatId, unsigned int, bool)=E2=80=99: > /home/user/libreoffice/include/rtl/string.hxx:280:32: note: at offset 0 t= o object =E2=80=98rtl::OString::OString(rtl::OStringConcat&&) [with= T1 =3D rtl::OStringConcat; T2 =3D rtl= ::OString]::Hack::c=E2=80=99 with size 1 declared here > 280 | struct Hack { char c; char a[]; }; > | ^ preceding the other warning.=