Can't configure ptrace in non-main thread

[theIDinside]

Using ptrace from another thread than the main thread, even if that thread is the one that does a fork + exec dance, will fail on PTRACE_SETOPTIONS call.

This behavior can be witnessed in the moved-main.cpp file in the rr-waitpid-bug repo.

Just building it with ./build.sh and then running it with

# this will work just fine
./tracer-moved-main

# this will fail by having ptrace setoptions fail
rr record ./tracer-moved-main