For reasons I do not understand, when searching for clues as to why my Eclispe Oxygen + CDT 9.3.2 running on Fedora 27 could not reliably debug my code, Google put up this question / answer as something to look at.
Basically my problem has been that a fairly simply C++ program, using C++ 11 features (specifically shared_ptr), was un-debuggable in Eclipse Oxygen 2 + CDT 9.3.2 on top of Fedora 27 (which has gdb version 8.0.1 installed from the standard package repo). Stepping into a few method calls resulted in a hung debug session, nothing going on, terminate Eclipse to recover.
If I debugged the binary using gdb on the command line, all was good; I could set break points, etc, everything worked as it should. But from inside Eclipse, nothing doing.
However, putting -std=c++11 into the project settings as shown by Andreas solved the problem. I have very little idea why. I thought I'd put this up in case someone else ran into a similar problem.
g++ is at version 7.2.1