Exercise on using the 'gdb' debugger with our 'esp.s' program
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1) preparing to use the debugger:

$ as -g esp.s -o esp.o
$ as -g eax2hex.s -o eax2hex.o
$ ld esp.o eax2hex.o -o esp
$ gdb esp


2) Executing the application under control of the debugger:

(gdb) li			// list instructions
(gdb) b 27			// set breakpoint
(gdb) run			// run until breakpoint is hit
(gdb) i r			// inspect CPU registers
(gdb) stepi			// single-step one instruction
(gdb) cont			// continue running program
(gdb) quit			// terminate the debugger