Just noticed in the GDB output that GDB is trying to run wrong executable. It so happened that I did forget to perform one step, deleting the original .cpp file and copy my own. Corrected that, refreshed the project and did a clean rebuild, but still same error:
No source file named /home/pratip/stm32plus-master/examples/usart_send_sync/usart_send_sync.cpp.
monitor halt
continue
Continuing.
Note: automatically using hardware breakpoints for read-only addresses.
Program received signal SIGINT, Interrupt.
main () at ../ESP8266Test.cpp:145
145 test.run();
No source file named /home/pratip/stm32plus-master/examples/usart_send_sync/usart_send_sync.cpp.
monitor halt
continue
Continuing.
Note: automatically using hardware breakpoints for read-only addresses.
Program received signal SIGINT, Interrupt.
main () at ../ESP8266Test.cpp:145
145 test.run();