为什么我在 GDB 上的断点有这个问题?GDB 停止 [英] Why do i have this problem with breakpoints on GDB? GDB Stops
问题描述
当调用函数 strcpy() 时，我尝试在 GDB 上设置断点，但 GDB 停止，我不知道如何找到错误，我是 GDB 新手我想研究二进制利用，所以我正在阅读的论坛对此没有任何解释，这是输出；
I tried to set a break-point on GDB when a function strcpy() is called, but GDB stops, and i don't know how to find the error, im new to GDB and i want to study binary exploitation, so the forum i'm reading does not explain nothing about this, here is the output;
(gdb) disassemble main
Dump of assembler code for function main:
0x00000000000011c9 <+0>: endbr64
0x00000000000011cd <+4>: push rbp
0x00000000000011ce <+5>: mov rbp,rsp
0x00000000000011d1 <+8>: sub rsp,0x50
0x00000000000011d5 <+12>: mov DWORD PTR [rbp-0x44],edi
0x00000000000011d8 <+15>: mov QWORD PTR [rbp-0x50],rsi
0x00000000000011dc <+19>: mov rax,QWORD PTR fs:0x28
0x00000000000011e5 <+28>: mov QWORD PTR [rbp-0x8],rax
0x00000000000011e9 <+32>: xor eax,eax
0x00000000000011eb <+34>: cmp DWORD PTR [rbp-0x44],0x1
0x00000000000011ef <+38>: jne 0x1207 <main+62>
0x00000000000011f1 <+40>: lea rsi,[rip+0xe10] # 0x2008
0x00000000000011f8 <+47>: mov edi,0x1
0x00000000000011fd <+52>: mov eax,0x0
0x0000000000001202 <+57>: call 0x10c0 <errx@plt>
0x0000000000001207 <+62>: mov DWORD PTR [rbp-0x34],0x0
0x000000000000120e <+69>: mov rax,QWORD PTR [rbp-0x50]
0x0000000000001212 <+73>: add rax,0x8
0x0000000000001216 <+77>: mov rdx,QWORD PTR [rax]
0x0000000000001219 <+80>: lea rax,[rbp-0x30]
0x000000000000121d <+84>: mov rsi,rdx
0x0000000000001220 <+87>: mov rdi,rax
0x0000000000001223 <+90>: call 0x1090 <strcpy@plt> // breakpoint here
0x0000000000001228 <+95>: mov eax,DWORD PTR [rbp-0x34]
0x000000000000122b <+98>: test eax,eax
0x000000000000122d <+100>: je 0x1247 <main+126>
0x000000000000122f <+102>: mov eax,DWORD PTR [rbp-0x34]
0x0000000000001232 <+105>: mov esi,eax
0x0000000000001234 <+107>: lea rdi,[rip+0xde5] # 0x2020
0x000000000000123b <+114>: mov eax,0x0
0x0000000000001240 <+119>: call 0x10d0 <printf@plt>
0x0000000000001245 <+124>: jmp 0x1253 <main+138>
0x0000000000001247 <+126>: lea rdi,[rip+0xe12] # 0x2060
0x000000000000124e <+133>: call 0x10a0 <puts@plt>
0x0000000000001253 <+138>: mov eax,0x0
0x0000000000001258 <+143>: mov rcx,QWORD PTR [rbp-0x8]
0x000000000000125c <+147>: xor rcx,QWORD PTR fs:0x28
0x0000000000001265 <+156>: je 0x126c <main+163>
0x0000000000001267 <+158>: call 0x10b0 <__stack_chk_fail@plt>
0x000000000000126c <+163>: leave
0x000000000000126d <+164>: ret
End of assembler dump.
(gdb) break *0x0000000000001223 // I want to set the breakpoint here
Breakpoint 1 at 0x1223
(gdb) r AAAA // I try to run the program providing arguments
Starting program: /home/ryan/liveoverflow_youtube/0x05_simple_crackme_intro_assembler/stackReg AAAA
[1]+ Stopped gdb stackReg // This is the problem?
推荐答案
GDB 像这样停止是一个错误，当 GDB 在尝试放置断点时抛出错误时，它已在上游 GDB 中通过此补丁修复:
GDB stopping like this is a bug which occurs when GDB throws an error while trying to place a breakpoint, it was fixed in upstream GDB with this patch:
https://sourceware.org/ml/gdb-patches/2019-05/msg00361.html
一旦你看到 GDB 像这样停止:
Once you see GDB stopped like this:
[1]+ Stopped
你应该被扔回一个shell.只需使用 fg 命令恢复 GDB 并继续您的调试会话.GDB 9 发布后，此错误将得到修复.
you should be dropped back to a shell. Just resume GDB with the fg command and continue your debug session. Once GDB 9 is out this bug will be fixed.
正如评论中指出的，断点地址不正确的原因是您使用的是与位置无关的可执行文件 (PIE)，当进程启动时，代码将被重新定位.
As was pointed out in a comment the reason the breakpoint address is incorrect is that you are using a Position Independent Executable (PIE), the code will be relocated when the process starts.
用starti启动GDB，然后你可以反汇编main，看看代码实际放在了哪里.
Start GDB with starti, then you can disassemble main and see where the code has actually been placed.
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