- you’re on 64-bit, so you probably want x/gx (or x/16gx, etc.) to print out 64-bit words (the g means “giant”). That’ll make the addresses on the stack more useful. (x/ax works too, and will attempt to resolve addresses to symbols if possible, at the cost of making the output not aligned in columns).
- the stack overflow is detected by using a canary value, basically a random series of bytes sitting after the string on the stack (your canary for example is 0x00 0x80 0xf7 0x8a 0x8a 0xbb 0x58 0xb6). This gets checked at the end of the function; on a mismatch, the function calls __stack_chk_fail which prints an error and aborts the program. The canary is pretty clever: it starts with a null byte so that it won’t be leaked by normal string functions, and the true canary is stored somewhere else in memory (not th stack) so it can’t be easily leaked or corrupted.