This question comes from a very popular assignment to teach assembly and the use of the GNU debugger. I am currently on phase 4 and here is the disassembled code:
Dump of assembler code for function phase_4:
0x08048f52 <+0>: push %ebp
0x08048f53 <+1>: mov %esp,%ebp
0x08048f55 <+3>: sub $0x28,%esp
0x08048f58 <+6>: lea -0xc(%ebp),%eax
0x08048f5b <+9>: mov %eax,0xc(%esp)
0x08048f5f <+13>: lea -0x10(%ebp),%eax
0x08048f62 <+16>: mov %eax,0x8(%esp)
0x08048f66 <+20>: movl $0x804a64c,0x4(%esp)
0x08048f6e <+28>: mov 0x8(%ebp),%eax
0x08048f71 <+31>: mov %eax,(%esp)
0x08048f74 <+34>: call 0x8048894 <__isoc99_sscanf@plt>
0x08048f79 <+39>: cmp $0x2,%eax
0x08048f7c <+42>: jne 0x8048f8b <phase_4+57>
0x08048f7e <+44>: mov -0xc(%ebp),%eax
0x08048f81 <+47>: cmp $0x1,%eax
0x08048f84 <+50>: jle 0x8048f8b <phase_4+57>
0x08048f86 <+52>: cmp $0x4,%eax
0x08048f89 <+55>: jle 0x8048f95 <phase_4+67>
0x08048f8b <+57>: nop
0x08048f8c <+58>: lea 0x0(%esi,%eiz,1),%esi
0x08048f90 <+62>: call 0x80493e1 <explode_bomb>
0x08048f95 <+67>: mov -0xc(%ebp),%eax
0x08048f98 <+70>: mov %eax,0x4(%esp)
0x08048f9c <+74>: movl $0x9,(%esp)
0x08048fa3 <+81>: call 0x8048c80 <func4>
0x08048fa8 <+86>: cmp -0x10(%ebp),%eax
0x08048fab <+89>: je 0x8048fb2 <phase_4+96>
0x08048fad <+91>: call 0x80493e1 <explode_bomb>
0x08048fb2 <+96>: leave
0x08048fb3 <+97>: ret
End of assembler dump.
What I have figured out so far is that it is expecting two numerical inputs that get passed to sscan. It is then checking if this is correct and continuing on.
Here is the code for func4 that gets called on line 81:
Dump of assembler code for function func4:
0x08048c80 <+0>: push %ebp
0x08048c81 <+1>: mov %esp,%ebp
0x08048c83 <+3>: sub $0x28,%esp
0x08048c86 <+6>: mov %ebx,-0xc(%ebp)
0x08048c89 <+9>: mov %esi,-0x8(%ebp)
0x08048c8c <+12>: mov %edi,-0x4(%ebp)
0x08048c8f <+15>: mov 0x8(%ebp),%esi
0x08048c92 <+18>: mov 0xc(%ebp),%ebx
0x08048c95 <+21>: test %esi,%esi
0x08048c97 <+23>: jg 0x8048ca0 <func4+32>
0x08048c99 <+25>: mov $0x0,%ebx
0x08048c9e <+30>: jmp 0x8048cc9 <func4+73>
0x08048ca0 <+32>: cmp $0x1,%esi
0x08048ca3 <+35>: je 0x8048cc9 <func4+73>
0x08048ca5 <+37>: mov %ebx,0x4(%esp)
0x08048ca9 <+41>: lea -0x1(%esi),%eax
0x08048cac <+44>: mov %eax,(%esp)
0x08048caf <+47>: call 0x8048c80 <func4>
0x08048cb4 <+52>: mov %eax,%edi
0x08048cb6 <+54>: mov %ebx,0x4(%esp)
0x08048cba <+58>: sub $0x2,%esi
0x08048cbd <+61>: mov %esi,(%esp)
0x08048cc0 <+64>: call 0x8048c80 <func4>
0x08048cc5 <+69>: add %eax,%edi
0x08048cc7 <+71>: add %edi,%ebx
0x08048cc9 <+73>: mov %ebx,%eax
0x08048ccb <+75>: mov -0xc(%ebp),%ebx
0x08048cce <+78>: mov -0x8(%ebp),%esi
0x08048cd1 <+81>: mov -0x4(%ebp),%edi
0x08048cd4 <+84>: mov %ebp,%esp
0x08048cd6 <+86>: pop %ebp
0x08048cd7 <+87>: ret
End of assembler dump.
Func4 seems to be the Fibonacci sequence called recursively. What I am having an issue with is the inputs that it is looking for, namely the comparison on line +86 because I know that if the values are equal it will jump to the solution. Any help from some assembly gurus would be appreciated.
