phase_2的汇编代码如下:
(gdb) disassemble phase_2
Dump of assembler code for function phase_2:
0x0000000000400efc <+0>: push %rbp
0x0000000000400efd <+1>: push %rbx
0x0000000000400efe <+2>: sub $0x28,%rsp
0x0000000000400f02 <+6>: mov %rsp,%rsi
0x0000000000400f05 <+9>: callq 0x40145c <read_six_numbers>
0x0000000000400f0a <+14>: cmpl $0x1,(%rsp)
0x0000000000400f0e <+18>: je 0x400f30 <phase_2+52>
0x0000000000400f10 <+20>: callq 0x40143a <explode_bomb>
0x0000000000400f15 <+25>: jmp 0x400f30 <phase_2+52>
0x0000000000400f17 <+27>: mov -0x4(%rbx),%eax
0x0000000000400f1a <+30>: add %eax,%eax
0x0000000000400f1c <+32>: cmp %eax,(%rbx)
0x0000000000400f1e <+34>: je 0x400f25 <phase_2+41>
0x0000000000400f20 <+36>: callq 0x40143a <explode_bomb>
0x0000000000400f25 <+41>: add $0x4,%rbx
0x0000000000400f29 <+45>: cmp %rbp,%rbx
0x0000000000400f2c <+48>: jne 0x400f17 <phase_2+27>
0x0000000000400f2e <+50>: jmp 0x400f3c <phase_2+64>
0x0000000000400f30 <+52>: lea 0x4(%rsp),%rbx
0x0000000000400f35 <+57>: lea 0x18(%rsp),%rbp
0x0000000000400f3a <+62>: jmp 0x400f17 <phase_2+27>
0x0000000000400f3c <+64>: add $0x28,%rsp
0x0000000000400f40 <+68>: pop %rbx
0x0000000000400f41 <+69>: pop %rbp
0x0000000000400f42 <+70>: retq
暂时我看不出这里面的一些门道,但是,根据这篇文章:
https://stackoverflow.com/questions/9186150/decoding-and-understanding-assembly-code
这里,因为rsp没有被push或者其他操作,所以,可以看做rsp减去0x28bytes, 也就是增加地址,
| sp | sp + 4 | sp + 8 | sp + c | sp + 10 | sp + 14 | rbp = sp + 18
且sp传递给了rsi, 应该是 read-six-numbers的参数,一个数组 t[5].
0x0000000000400f05 <+9>: callq 0x40145c <read_six_numbers>
0x0000000000400f0a <+14>: cmpl $0x1,(%rsp)
0x0000000000400f0e <+18>: je 0x400f30 <phase_2+52>
0x0000000000400f10 <+20>: callq 0x40143a <explode_bomb>
类似于同于:
if (t[0] == 1)
...
else
explode_bomb
然后看一下 +52处
0x0000000000400f30 <+52>: lea 0x4(%rsp),%rbx
0x0000000000400f35 <+57>: lea 0x18(%rsp),%rbp // 好像回退了,这一句和上面的layout联系起来
0x0000000000400f3a <+62>: jmp 0x400f17 <phase_2+27>
-----------------------+27---------------------
0x0000000000400f17 <+27>: mov -0x4(%rbx),%eax
0x0000000000400f1a <+30>: add %eax,%eax
0x0000000000400f1c <+32>: cmp %eax,(%rbx)
0x0000000000400f1e <+34>: je 0x400f25 <phase_2+41>
或者等于:
eax == rbx[-4](eax=t[1])
eax += eax
0x0000000000400f25 <+41>: add $0x4,%rbx
0x0000000000400f29 <+45>: cmp %rbp,%rbx
0x0000000000400f2c <+48>: jne 0x400f17 <phase_2+27>
0x0000000000400f2e <+50>: jmp 0x400f3c <phase_2+64>
(gdb) disassemble read_six_numbers
Dump of assembler code for function read_six_numbers:
0x000000000040145c <+0>: sub $0x18,%rsp
0x0000000000401460 <+4>: mov %rsi,%rdx
0x0000000000401463 <+7>: lea 0x4(%rsi),%rcx
0x0000000000401467 <+11>: lea 0x14(%rsi),%rax
0x000000000040146b <+15>: mov %rax,0x8(%rsp)
0x0000000000401470 <+20>: lea 0x10(%rsi),%rax
0x0000000000401474 <+24>: mov %rax,(%rsp)
0x0000000000401478 <+28>: lea 0xc(%rsi),%r9
0x000000000040147c <+32>: lea 0x8(%rsi),%r8
0x0000000000401480 <+36>: mov $0x4025c3,%esi
0x0000000000401485 <+41>: mov $0x0,%eax
0x000000000040148a <+46>: callq 0x400bf0 <__isoc99_sscanf@plt>
0x000000000040148f <+51>: cmp $0x5,%eax
0x0000000000401492 <+54>: jg 0x401499 <read_six_numbers+61>
0x0000000000401494 <+56>: callq 0x40143a <explode_bomb>
0x0000000000401499 <+61>: add $0x18,%rsp
0x000000000040149d <+65>: retq
End of assembler dump.
---------------------------
End of assembler dump.
(gdb) x/s 0x4025c3
0x4025c3: "%d %d %d %d %d %d"