We will now set a break point for debugging our code by entering:
This will set a break point at the beginning of the _start label.
We can now begin our program execution by entering:
Your terminal should now look similar to the output below:
break _start
We can now begin our program execution by entering:
run
|-Register group: general------------------------------------------------------------------------------------------------------------------------------------------------| |eax 0x0 0 ecx 0x0 0 edx 0x0 0 | |ebx 0x0 0 esp 0xffffd950 0xffffd950 ebp 0x0 0x0 | |esi 0x0 0 edi 0x0 0 eip 0x8049000 0x8049000 <_start> | |eflags 0x202 [ IF ] cs 0x23 35 ss 0x2b 43 | |ds 0x2b 43 es 0x2b 43 fs 0x0 0 | |gs 0x0 0 k0 0x0 0 k1 0x0 0 | |k2 0x0 0 k3 0x0 0 k4 0x0 0 | |k5 0x0 0 k6 0x0 0 k7 0x0 0 | | | | | | | | | | | | | | | | | | | | | | | |------------------------------------------------------------------------------------------------------------------------------------------------------------------------| |B+> 0x8049000 <_start> mov eax,0x4 | | 0x8049005 <_start+5> mov ebx,0x1 | | 0x804900a <_start+10> lea ecx,ds:0x804a000 | | 0x8049010 <_start+16> mov edx,0xd | | 0x8049015 <_start+21> int 0x80 | | 0x8049017 <print_hex_message> mov eax,0x4 | | 0x804901c <print_hex_message+5> mov ebx,0x1 | | 0x8049021 <print_hex_message+10> lea ecx,ds:0x804a00d | | 0x8049027 <print_hex_message+16> mov edx,0xd | | 0x804902c <print_hex_message+21> int 0x80 | | 0x804902e <exit_program> mov eax,0x1 | | 0x8049033 <exit_program+5> mov ebx,0x0 | | 0x8049038 <exit_program+10> int 0x80 | | 0x804903a add BYTE PTR [eax],al | | 0x804903c add BYTE PTR [eax],al | | 0x804903e add BYTE PTR [eax],al | | 0x8049040 add BYTE PTR [eax],al | | 0x8049042 add BYTE PTR [eax],al | | 0x8049044 add BYTE PTR [eax],al | | 0x8049046 add BYTE PTR [eax],al | |------------------------------------------------------------------------------------------------------------------------------------------------------------------------| native process 84922 In: _start L?? PC: 0x8049000 (gdb) lay reg (gdb) break _start Breakpoint 1 at 0x8049000 (gdb) run Starting program: /home/pete/Documents/ASM/hello_world/x86/hello_x86 Breakpoint 1, 0x08049000 in _start () (gdb)
Our program is now running inside the debugger. We can see that our breakpoint was set at the beginning of the _start label which is at
memory address 0x0804900. The first instruction at that address should be highlighted in the assembly frame, and if we look at the register group,
we can see that our eip register has the address of the next instruction to mov 0x4 into eax.