libstdc++ 文件系统中未初始化的用法?

Question

请考虑以下代码：

#include <filesystem>
int main() {
std::filesystem::path p{"/"};
}

当使用带有标志的 clang10 进行编译时-std=c++17 -fsanitize=memory -g -O1 -stdlib=libstdc++它编译完全正常，但在运行时，内存清理器发现以下错误：

==166467==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x560e38eafc41 in std::basic_ostream<char, std::char_traits<char> >& std::__detail::operator<<<char, std::char_traits<char>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&>(std::basic_ostream<char, std::char_traits<char> >&, std::__detail::_Quoted_string<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, char> const&) /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../include/c++/10.1.0/bits/quoted_string.h:124:32
#1 0x560e38eaf03c in std::basic_ostream<char, std::char_traits<char> >& std::filesystem::__cxx11::operator<<<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, std::filesystem::__cxx11::path const&) /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../include/c++/10.1.0/bits/fs_path.h:441:7
#2 0x560e38eaecdb in main ~/test/test.cpp:15:15
#3 0x7f5d0fa58001 in __libc_start_main (/usr/lib/libc.so.6+0x27001)
#4 0x560e38e3033d in _start (~/test/a.out+0x2133d)
SUMMARY: MemorySanitizer: use-of-uninitialized-value /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/10.1.0/../../../../include/c++/10.1.0/bits/quoted_string.h:124:32 in std::basic_ostream<char, std::char_traits<char> >& std::__detail::operator<<<char, std::char_traits<char>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&>(std::basic_ostream<char, std::char_traits<char> >&, std::__detail::_Quoted_string<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, char> const&)
Exiting

使用-stdlib=libc++编译时，它完全可以正常工作。另请参阅Godbolt(可悲的是，MSAN输出在那里有点非描述性(。

是内存消毒剂过分热心还是有什么问题？我简要地查看了有问题的文件和代码

for (auto __c : __str._M_string)
{
if (__c == __str._M_delim || __c == __str._M_escape) // <- line 124
__ostr << __str._M_escape;
__ostr << __c;
}

对我来说似乎还可以(__str属于std::__detail::_Quoted_string<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&类型，只有一个用户定义的构造函数，该值从参数初始化所有三个成员(。

clang++ -v输出：

clang version 10.0.0 
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-pc-linux-gnu/10.1.0
Found candidate GCC installation: /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/10.1.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0
Found candidate GCC installation: /usr/lib64/gcc/x86_64-pc-linux-gnu/10.1.0
Selected GCC installation: /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/10.1.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64

Answer 1

这是一个误报。

您应该将其报告为清理器错误;它似乎与问题 1238 类似。