Hi Brian Kelly
Every project has to pass through the Reset_handler, and then go to the initialization part and then jump to main part. This doesn't seams to be a debugger problem but a problem in the program. I would expect that you already test this code with a IDE, if not, please try to first test the project with an IDE and also try to locate the problem in your UART setup, I noticed that you are in the default_IRS handler, It could be that you do not enable the gated clock before you use the peripheral, which leads to the hardfault error.
Hope this could help you.
Best Regards
Jorge Alcala