Warning stringop-overflow with gcc-10.3.0

[gsjaardema]

I get the following warning when compiling fmt-10.2.1 using g++-10.3.0 with -O3 optimization:

[ 33%] Building CXX object CMakeFiles/fmt.dir/src/format.cc.o
In file included from /fgs/code/TPL/fmt/fmt/include/fmt/format-inl.h:25,
                 from /fgs/code/TPL/fmt/fmt/src/format.cc:8:
In function 'fmt::v10::detail::format_decimal_result<Char*> fmt::v10::detail::format_decimal(Char*, UInt, int) [with Char = char; UInt = unsigned int]',
    inlined from 'constexpr fmt::v10::detail::format_decimal_result<Iterator> fmt::v10::detail::format_decimal(Iterator, UInt, int) [with Char = char; UInt = unsigned int; Iterator = fmt::v10::appender; typename std::enable_if<(! std::is_pointer<typename std::remove_cv<typename std::remove_reference<_Arg>::type>::type>::value), int>::type <anonymous> = 0]' at /fgs/code/TPL/fmt/fmt/include/fmt/format.h:1375:28,
    inlined from 'void fmt::v10::detail::format_hexfloat(Float, int, fmt::v10::detail::float_specs, fmt::v10::detail::buffer<char>&) [with Float = double; typename std::enable_if<(! std::integral_constant<bool, (std::numeric_limits<_Tp>::digits == 106)>::value), int>::type <anonymous> = 0]' at /fgs/code/TPL/fmt/fmt/include/fmt/format.h:3253:23:
/fgs/code/TPL/fmt/fmt/include/fmt/format.h:1331:11: warning: writing 2 bytes into a region of size 0 [-Wstringop-overflow=]
 1331 |     memcpy(dst, src, 2);
      |     ~~~~~~^~~~~~~~~~~~~
/fgs/code/TPL/fmt/fmt/include/fmt/format.h: In function 'void fmt::v10::detail::format_hexfloat(Float, int, fmt::v10::detail::float_specs, fmt::v10::detail::buffer<char>&) [with Float = double; typename std::enable_if<(! std::integral_constant<bool, (std::numeric_limits<_Tp>::digits == 106)>::value), int>::type <anonymous> = 0]':
/fgs/code/TPL/fmt/fmt/include/fmt/format.h:1374:8: note: at offset -2 to object 'buffer' with size 10 declared here
 1374 |   Char buffer[digits10<UInt>() + 1] = {};
      |        ^~~~~~
[ 66%] Building CXX object CMakeFiles/fmt.dir/src/os.cc.o

[gsjaardema]

Might be duplicate of #2708

[vitaut]

Yeah, it's essentially the same issue (a gcc bug). It should be fixed in gcc 11 and in the meantime you could suppress it with FMT_SYSTEM or other means.