Bug(?) of libstdc++ (COW is still used)

[Takashi Yano]

Hi,

I noticed that the libstdc++ on Cygwin still uses COW (copy-on-write),
which is inhibited since C++11.

The following code:

#include <string>
#include <cassert>
#include <cstdio>

int main()
{
	std::string a("AAAA");
	std::string b;
	b = a;
    
	printf("%d\n", _GLIBCXX_USE_CXX11_ABI);
	printf("%p, %p: %s\n", a.c_str(), b.c_str(), b.c_str());
	b[0] = 'B';
	printf("%p, %p: %s\n", a.c_str(), b.c_str(), b.c_str());

    return 0;
}

outputs

0
0xa00000648, 0xa00000648: AAAA
0xa00000648, 0xa00000568: BAAA

$ cygcheck -c libstdc++6
Cygwin Package Information
Package              Version    Status
libstdc++6           14.4.0-1       OK

Due to this, glslc in shaderc package sometimes crashes in libglslang.a
because of Use-After-Free problem.

Is there any reason that libstdc++ on Cygwin still uses COW
(_GLIBCXX_USE_CXX11_ABI = 0 setting), even though it is inhibited
since C++11?

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>