如何设置最早的断点

Question

我试图在模块加载到 gdb 后立即停止。假设二进制完全去掉了所有符号信息，所以没有main。

理想情况下，我会在入口点设置断点，但这个想法由于重定位而失效：

(gdb) info target
Symbols from "./application".
Local exec file:
    `./application', file type elf64-x86-64.
    Entry point: 0xc154
...
(gdb) break *0xc154
Breakpoint 1 at 0xc154
(gdb) r
Starting program: ./application 
Warning:
Cannot insert breakpoint 1.
Error accessing memory address 0xc154: Input/output error.

(gdb) info target
Symbols from "./application".
Unix child process:
    Using the running image of child process 22835.
    While running this, GDB does not access memory from...
Local exec file:
    `./application', file type elf64-x86-64.
    Entry point: 0x555555560154

即使这种方法有效（我可以在新地址上设置一个新断点并禁用原始地址），它也不能通过 gdb 脚本/批处理模式轻松执行，因为它中间有一条失败的指令。

有没有办法做到这一点？理想情况下，像“运行单指令”而不是“运行”这样的东西会很有用。

Answer 1

更新：

GDB-8.1 实现了starti 命令，这使得这很容易。

---

入口点：0xc154

这是一个动态链接的、与位置无关的 (PIE) 二进制文件。

您希望在该二进制文件加载并重定位之后，但在它执行任何操作之前停止动态链接器。

(gdb) set stop-on-solib-events 1
(gdb) run
Starting program: /tmp/a.out 
Stopped due to shared library event (no libraries added or removed)
(gdb) info target
Symbols from "/tmp/a.out".
Unix child process:
        Using the running image of child process 13746.
        While running this, GDB does not access memory from...
Local exec file:
        `/tmp/a.out', file type elf64-x86-64.
        Entry point: 0x5555555545f0
        ...

(gdb) bt
#0  __GI__dl_debug_state () at dl-debug.c:77
#1  0x00007ffff7ddd488 in dl_main (phdr=<optimized out>, phnum=<optimized out>, user_entry=<optimized out>, auxv=0x7ffff7ffe870) at rtld.c:1678
#2  0x00007ffff7defb24 in _dl_sysdep_start (start_argptr=<optimized out>, dl_main=0x7ffff7ddc6e0 <dl_main>) at ../elf/dl-sysdep.c:244
#3  0x00007ffff7ddf365 in _dl_start_final (arg=0x7fffffffe440) at rtld.c:338
#4  _dl_start (arg=0x7fffffffe440) at rtld.c:564
#5  0x00007ffff7ddb6b8 in _start () from /lib64/ld-linux-x86-64.so.2