https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92893
--- Comment #9 from Stephan Bergmann <sbergman at redhat dot com> ---
(In reply to Martin Sebor from comment #2)
> Defining Str like so works for the test case:
>
> struct Str {
> template<typename T1, typename T2> Str(Cat<T1, T2> c)
> {
> struct Flex { char c, a[]; } *p = (Flex*)get();
> c.add(p->a);
> }
> };
So I had created <https://gerrit.libreoffice.org/c/core/+/85161> "Silence bogus
-Wstringop-overflow with GCC trunk towards GCC 10" back in last December, and
it sufficed to suppress all those warnings when compiling LibreOffice with
then-trunk GCC, with optimizations enabled. However, meanwhile GCC has changed
again so that at least one place in the LibreOffice code now produces two
-Werror=stringop-overflow= 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 <mse...@redhat.com>
> Date: Sat Dec 14 00:52:46 2019 +0000
>
> 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-test.cxx:14:
> In member function ‘char* rtl::OStringConcat<T1, T2>::addData(char*) const
> [with T1 = rtl::OStringLiteral; T2 = const char [2]]’,
> inlined from ‘char* rtl::OStringConcat<T1, T2>::addData(char*) const
> [with T1 = rtl::OStringConcat<rtl::OStringLiteral, const char [2]>; T2 =
> rtl::OString]’ at /home/user/libreoffice/include/rtl/stringconcat.hxx:256:114,
> inlined from ‘rtl::OString::OString(rtl::OStringConcat<T1, T2>&&) [with
> T1 = rtl::OStringConcat<rtl::OStringLiteral, const char [2]>; T2 =
> rtl::OString]’ at /home/user/libreoffice/include/rtl/string.hxx:281:34,
> inlined from ‘void test::FiltersTest::recursiveScan(test::filterStatus,
> const rtl::OUString&, const rtl::OUString&, const rtl::OUString&,
> SfxFilterFlags, SotClipboardFormatId, unsigned int, bool)’ at
> /home/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=stringop-overflow=]
> 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-test.cxx:14:
> /home/user/libreoffice/include/rtl/string.hxx: In member function ‘void
> test::FiltersTest::recursiveScan(test::filterStatus, const rtl::OUString&,
> const rtl::OUString&, const rtl::OUString&, SfxFilterFlags,
> SotClipboardFormatId, unsigned int, bool)’:
> /home/user/libreoffice/include/rtl/string.hxx:280:32: note: at offset 0 to
> object ‘rtl::OString::OString(rtl::OStringConcat<T1, T2>&&) [with T1 =
> rtl::OStringConcat<rtl::OStringLiteral, const char [2]>; T2 =
> rtl::OString]::Hack::c’ with size 1 declared here
> 280 | struct Hack { char c; char a[]; };
> | ^
and later
> commit a9a437ffc4269650e34af92c4fb095b7ed98f94a
> Author: Jakub Jelinek <ja...@redhat.com>
> Date: Tue Mar 17 13:36:41 2020 +0100
>
> 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-test.cxx:14:
> In function ‘char* rtl::addDataHelper(char*, const char*, std::size_t)’,
> inlined from ‘static char*
> rtl::ToStringHelper<rtl::OStringLiteral>::addData(char*, const
> rtl::OStringLiteral&)’ at
> /home/user/libreoffice/include/rtl/string.hxx:1907:91,
> inlined from ‘char* rtl::OStringConcat<T1, T2>::addData(char*) const
> [with T1 = rtl::OStringLiteral; T2 = const char [2]]’ at
> /home/user/libreoffice/include/rtl/stringconcat.hxx:222:103,
> inlined from ‘char* rtl::OStringConcat<T1, T2>::addData(char*) const
> [with T1 = rtl::OStringConcat<rtl::OStringLiteral, const char [2]>; T2 =
> rtl::OString]’ at /home/user/libreoffice/include/rtl/stringconcat.hxx:256:114,
> inlined from ‘rtl::OString::OString(rtl::OStringConcat<T1, T2>&&) [with
> T1 = rtl::OStringConcat<rtl::OStringLiteral, const char [2]>; T2 =
> rtl::OString]’ at /home/user/libreoffice/include/rtl/string.hxx:281:34,
> inlined from ‘void test::FiltersTest::recursiveScan(test::filterStatus,
> const rtl::OUString&, const rtl::OUString&, const rtl::OUString&,
> SfxFilterFlags, SotClipboardFormatId, unsigned int, bool)’ at
> /home/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=stringop-overflow=]
> 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-test.cxx:14:
> /home/user/libreoffice/include/rtl/string.hxx: In member function ‘void
> test::FiltersTest::recursiveScan(test::filterStatus, const rtl::OUString&,
> const rtl::OUString&, const rtl::OUString&, SfxFilterFlags,
> SotClipboardFormatId, unsigned int, bool)’:
> /home/user/libreoffice/include/rtl/string.hxx:280:32: note: at offset 0 to
> object ‘rtl::OString::OString(rtl::OStringConcat<T1, T2>&&) [with T1 =
> rtl::OStringConcat<rtl::OStringLiteral, const char [2]>; T2 =
> rtl::OString]::Hack::c’ with size 1 declared here
> 280 | struct Hack { char c; char a[]; };
> | ^
preceding the other warning.
