Not true. GCC broke compatibility with the memory layout of are string at c++11 and passing those between DLLs with versions of GCC on either side of that change will crash.

The standard doesn't specify memory layout or ABI so as a general rule you can't do this. You can get around it by depending on implementation details like what is implicitly done by chromium

Now you are changing the subject. Allocation, which was the subject, happens the same way on either side of gcc's C++11 boundary. The C++11 break was required by the ISO Standard issued in 2011.

The Gcc and libstdc++ maintainers are extremely careful to maintain ABI compatibility between widely-separated releases, where permitted by the Standard. You can happily call between code compiled with gcc-6 and gcc-10, release or debug, optimized or not.

It is possible to deliberately vary ABI with compiler options, but nobody uses those for shared libraries they distribute, for obvious reasons, with the unique exception of choosing pre-C++11 vs post-C++11 ABI.

I guess you're right. I still am wary about depending on this given the current conversation about ABI evolution with C++. And given that lots of languages can interop with C I think building C interfaces between binaries buys options