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GDB#xff08;GNU Debugger#xff09;是一个用于调试程序的强大工具。它是GNU项目的一部分#xff0c;支持多种编程语言#xff0c;包括C、C等。GDB 提供了一组命令和功能#xff0c;允许跟踪检查程序的内部状态#xff0c;跟踪代码的执行过程#…概念
GDBGNU Debugger是一个用于调试程序的强大工具。它是GNU项目的一部分支持多种编程语言包括C、C等。GDB 提供了一组命令和功能允许跟踪检查程序的内部状态跟踪代码的执行过程以及定位和修复程序中的错误。
gdb和gdb sever
GDBGNU Debugger
gdb 用于本地调试程序。它允许程序员查看程序的运行状态、检查变量和内存、设置断点等以便在代码中找到和修复问题。使用 gdb 时你在本地计算机上运行 gdb并且该调试器直接与正在调试的程序进行交互。
GDB Servergdbserver
gdbserver 是 GDB 的另一部分用于远程调试。它允许你在目标计算机上运行一个小型的 GDB 服务器然后在本地计算机上运行gdb 与之连接。通过 gdbserver你可以在嵌入式系统或远程计算机上调试程序而不需要将整个 GDB 调试器放在目标系统上。这种分离的方法对于嵌入式系统等资源受限的环境非常有用允许在目标系统上运行轻量级的 gdbserver而在开发机上运行完整版的 gdb 进行调试。
作用
调试程序 GDB的主要作用是帮助程序员识别和解决程序中的错误bugs。它允许开发者在程序执行时停下来检查变量的值查看函数调用堆栈设置断点并逐步执行代码。变量和内存查看GDB 允许开发者检查程序运行时的变量的值和内存的内容。这对于理解程序的状态以及发现潜在问题非常有用。设置断点 开发者可以在程序中设置断点使得程序在执行到达特定的位置时停下来。这有助于逐步调试程序并检查特定的代码段。单步执行GDB 允许开发者逐步执行程序一次执行一行代码或一次执行一个函数。这对于追踪程序的执行流程非常有用。追踪函数调用GDB 能够跟踪程序中的函数调用显示函数调用关系帮助开发者理解程序的执行路径。查找内存错误GDB 能够帮助开发者查找程序中的内存错误如访问未分配内存、内存溢出等问题。多线程调试GDB 支持调试多线程程序允许开发者查看和调试不同线程的执行状态。核心转储分析当程序发生崩溃时GDB 可以分析核心转储文件帮助开发者定位问题的根本原因。
GDB和IDE差别
各有好处并且IDE在不考虑环境的情况下更容易上手基于 Linux 服务器等的无图形界面开发使用 VimGDB 可以在任意一台电脑上直接调试不用花时间安装复杂的 IDE 环境。
主要包含如下区别:
命令行界面 vs 图形用户界面功能的可视化和图形化展示集成性和便利性快捷键和工具栏平台和语言支持
总体而言使用 GDB 和使用 IDE 中的调试工具之间的选择通常取决于个人偏好、项目需求以及开发环境。
gdb 调试段错误代码demo
#include stdio.hvoid accessInvalidMemory() {int *ptr NULL; // 故意将指针设置为NULL*ptr 42; // 试图访问NULL指针
}
int main() {accessInvalidMemory(); // 调用会导致Segmentation fault的函数return 0;
}定位流程与操作
ubuntu:$ gcc -g Segmentation_fault.c -o Segmentation_fault
ubuntu:GDB_debug$ gdb ./Segmentation_fault -q
Reading symbols from ./Segmentation_fault...done.
(gdb) b main
Breakpoint 1 at 0x617: file Segmentation_fault.c, line 9.
(gdb) list
1 #include stdio.h
2
3 void accessInvalidMemory() {
4 int *ptr NULL; // 故意将指针设置为NULL
5 *ptr 42; // 试图访问NULL指针
6 }
7
8 int main() {
9 accessInvalidMemory(); // 调用会导致Segmentation fault的函数
10 return 0;
(gdb) r
Starting program: GDB_debug/Segmentation_faultBreakpoint 1, main () at Segmentation_fault.c:9
9 accessInvalidMemory(); // 调用会导致Segmentation fault的函数
(gdb) s
accessInvalidMemory () at Segmentation_fault.c:4
4 int *ptr NULL; // 故意将指针设置为NULL
(gdb) n
5 *ptr 42; // 试图访问NULL指针
(gdb) nProgram received signal SIGSEGV, Segmentation fault.
0x000055555555460a in accessInvalidMemory () at Segmentation_fault.c:5
5 *ptr 42; // 试图访问NULL指针
(gdb) bt
#0 0x000055555555460a in accessInvalidMemory () at Segmentation_fault.c:5
#1 0x0000555555554621 in main () at Segmentation_fault.c:9
(gdb) n
Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.
(gdb) n
The program is not being run.结论 查看调用栈
(gdb) bt
#0 0x000055555555460a in accessInvalidMemory () at Segmentation_fault.c:5
#1 0x0000555555554621 in main () at Segmentation_fault.c:9问题出在函数accessInvalidMemory代码的第五行
说明与解释
bt是backtrace的缩写可以查看调用栈r是run的缩写n是next的缩写s是step的缩写b 是break的缩写quit 退出gdb调试缩写为q
为什么不一直用next还用step
next执行当前函数的所有指令而step可以让进入段错误函数后再第一行停下来可以定位到具体到某一行出现的问题
GDB多线程调试
#include stdio.h
#include pthread.h
#include unistd.hvoid *thread_function(void *arg) {for (int i 0; i 5; i) {printf(Thread %ld: Iteration %d\n, (long)arg, i);sleep(1);}return NULL;
}int main() {pthread_t thread1, thread2;// 创建两个线程pthread_create(thread1, NULL, thread_function, (void *)1);pthread_create(thread2, NULL, thread_function, (void *)2);// 等待线程结束pthread_join(thread1, NULL);pthread_join(thread2, NULL);return 0;
}编译
gcc -g multithread_demo.c -o multithread_demo -lpthread执行
gdb ./multithread_demo -q想要完成的调试方法
1、查看整体进程中的线程执行结果
ubuntu:$ gdb ./multithread_demo -q
Reading symbols from ./multithread_demo...done.
(gdb) b main
Breakpoint 1 at 0x81d: file multithread_demo.c, line 13.
(gdb) run
Starting program: GDB_debug/multithread_demo
[Thread debugging using libthread_db enabled]
Using host libthread_db library /lib/x86_64-linux-gnu/libthread_db.so.1.
Breakpoint 1, main () at multithread_demo.c:13
13 int main() {
(gdb) n
17 pthread_create(thread1, NULL, thread_function, (void *)1);
(gdb) n
[New Thread 0x7ffff77c2700 (LWP 335)]
18 pthread_create(thread2, NULL, thread_function, (void *)2);
(gdb) info threads
Id Target Id Frame
- 1 Thread 0x7ffff7fdb740 (LWP 130537) multithread_dem main () at multithread_demo.c:18
(gdb) n
Thread 1: Iteration 1
Thread 2: Iteration 0
Thread 1: Iteration 2
Thread 2: Iteration 1
Thread 1: Iteration 3
Thread 2: Iteration 2
Thread 1: Iteration 4
Thread 2: Iteration 3
[Thread 0x7ffff77c2700 (LWP 335) exited]
22 pthread_join(thread2, NULL);
(gdb) n
Thread 2: Iteration 4
[Thread 0x7ffff6fc1700 (LWP 1407) exited]
24 return 0;
(gdb) n
25 }
(gdb) n
[Inferior 1 (process 130537) exited normally]
(gdb) n
The program is not being run.2、子线程被创建后gdb跟踪子线程及主线程 ubuntu:GDB_debug$ gdb ./multithread_demo -q
Reading symbols from ./multithread_demo...done.
(gdb) set detach-on-fork off
(gdb) b main
Breakpoint 1 at 0x81d: file multithread_demo.c, line 13.
(gdb) run
Starting program: GDB_debug/multithread_demo
[Thread debugging using libthread_db enabled]
13 int main() {
(gdb) n
17 pthread_create(thread1, NULL, thread_function, (void *)1);
(gdb) n
[New Thread 0x7ffff77c2700 (LWP 9522)]
Thread 1: Iteration 0
18 pthread_create(thread2, NULL, thread_function, (void *)2);
(gdb) n
[New Thread 0x7ffff6fc1700 (LWP 9523)]
Thread 2: Iteration 0
Thread 2: Iteration 1
Thread 2: Iteration 2
Thread 2: Iteration 3
Thread 2: Iteration 4
8 sleep(1);
(gdb)
6 for (int i 0; i 5; i) {
(gdb)
7 printf(Thread %ld: Iteration %d\n, (long)arg, i);
(gdb)
Thread 1: Iteration 1
8 sleep(1);
(gdb)
6 for (int i 0; i 5; i) {
(gdb)
7 printf(Thread %ld: Iteration %d\n, (long)arg, i);
(gdb)
Thread 1: Iteration 2
8 sleep(1);
(gdb)
6 for (int i 0; i 5; i) {
(gdb)
7 printf(Thread %ld: Iteration %d\n, (long)arg, i);
(gdb)
Thread 1: Iteration 3
8 sleep(1);
(gdb)
6 for (int i 0; i 5; i) {
(gdb)
7 printf(Thread %ld: Iteration %d\n, (long)arg, i);
(gdb)
Thread 1: Iteration 4
8 sleep(1);
(gdb)
6 for (int i 0; i 5; i) {
(gdb)
10 return NULL;
(gdb)
11 }命令解释
set detach-on-fork off 告诉 GDB 在子进程或线程分离时不要自动分离调试器默认情况下GDB 会在程序中发生 fork 时自动分离调试器这可能导致你失去对子进程的控制所以我一般会设置为offshow detach-on-fork可以看当前的设置状态
GDB多进程调试
#include stdio.h
#include unistd.h
int main()
{pid_t pid fork();if(pid 0){int num 10;while(num10){sleep(2);printf(this 1is child,pid %d\n,getpid());}printf(this 2is child,pid %d\n,getpid());printf(this 3is child,pid %d\n,getpid());}else{int mnum5;while(mnum5){sleep(5);printf(this 4is parent,pid %d\n,getpid());}}return 0;
}编译
gcc -g multiprocess_demo_2.c -o multiprocess_demo_2gdb 跟踪子进程
ubuntu:GDB_debug$ gcc -g multiprocess_demo_2.c -o multiprocess_demo_2
ubuntu:GDB_debug$ gdb ./multiprocess_demo_2 -q
Reading symbols from ./multiprocess_demo_2...done.
(gdb) b main
Breakpoint 1 at 0x722: file multiprocess_demo_2.c, line 5.
(gdb) set follow-fork-mode child
(gdb) r
Starting program: /home/xj/Desktop/huangrui/project_1/GDB_debug/multiprocess_demo_2Breakpoint 1, main () at multiprocess_demo_2.c:5
5 pid_t pid fork();
(gdb) n
[New process 109167]
[Switching to process 109167]
main () at multiprocess_demo_2.c:6
6 if(pid 0)
(gdb) info inferiorsNum Description Executable1 null GDB_debug/multiprocess_demo_2
* 2 process 109167 GDB_debug/multiprocess_demo_2
(gdb) this 4is parent,pid 109163
this 4is parent,pid 109163
n
8 int num 10;
(gdb) n
9 while(num10){
(gdb) this 4is parent,pid 109163
n
10 sleep(2);
(gdb) n
11 printf(this 1is child,pid %d\n,getpid());
(gdb) this 4is parent,pid 109163
p numthis 4is parent,pid 109163
9
$1 9
(gdb) n
this 1is child,pid 109167
9 while(num10){
(gdb) n
14 printf(this 2is child,pid %d\n,getpid());
(gdb) n
this 2is child,pid 109167
15 printf(this 3is child,pid %d\n,getpid());
(gdb) this 4is parent,pid 109163
n
this 3is child,pid 109167
26 return 0;
(gdb) n
27 }(gdb) nthis 4is parent,pid 109163__libc_start_main (main0x55555555471a main, argc1, argv0x7fffffffe328, initoptimized out, finioptimized out, rtld_finioptimized out, stack_end0x7fffffffe318)at ../csu/libc-start.c:344
344 ../csu/libc-start.c: No such file or directory.
(gdb) n
[Inferior 2 (process 109167) exited normally]
(gdb) n
The program is not being run.
(gdb) quitthis 4is parent,pid 109163set follow-fork-mode的作用set follow-fork-mode parent 是 GDB 的一个命令用于在多进程调试时控制在 fork() 调用之后 GDB 应该跟踪哪个进程。
set follow-fork-mode parent 设置 GDB 在 fork()调用后继续跟踪父进程而不是默认的子进程。这意味着在程序执行 fork() 后GDB将继续调试父进程而子进程将被分离detach。set follow-fork-mode child 设置 GDB 在 fork()调用后继续跟踪子进程而不是默认的父进程。这意味着在程序执行 fork() 后GDB 将继续调试子进程而父进程将被分离。set follow-fork-mode ask 设置 GDB 在 fork() 调用后询问用户要跟踪哪个进程。GDB 将在每次 fork() 发生时等待用户输入以确定是跟踪父进程还是子进程。
解释
补充
在 GDB 中使用 p 命令print 的缩写不仅可以用来查看变量的值还可以用来修改变量的值。当你执行 p num9 时实际上是在给变量 num 赋予新的值。
前面是单子进程的调试
那如果我父进程创建多个子进程应该如何调试呢
#include stdio.h
#include unistd.hint main() {pid_t pid1, pid2;pid1 fork();if (pid1 0) {// 子进程1printf(Child Process 1 (PID: %d)\n, getpid());// 子进程1的工作} else {pid2 fork();if (pid2 0) {// 子进程2printf(Child Process 2 (PID: %d)\n, getpid());// 子进程2的工作} else {// 父进程printf(Parent Process (PID: %d)\n, getpid());// 父进程的工作// 父进程通常需要等待子进程结束waitpid(pid1, NULL, 0);waitpid(pid2, NULL, 0);}}return 0;
}调试步骤步骤有删减
ubuntu:GDB_debug$ gdb ./multiprocess_demo -q
Reading symbols from ./multiprocess_demo...done.
(gdb) b main
Breakpoint 1 at 0x722: file multiprocess_demo.c, line 7.
(gdb) b fork
Breakpoint 2 at 0x5f0
(gdb) set detach-on-fork off
(gdb) set follow-fork-mode child
(gdb) catch fork
Catchpoint 3 (fork)
(gdb) run
Starting program: GDB_debug/multiprocess_demoBreakpoint 1, main () at multiprocess_demo.c:7
7 pid1 fork();
(gdb) nBreakpoint 2, __libc_fork () at ../sysdeps/nptl/fork.c:49
49 ../sysdeps/nptl/fork.c: No such file or directory.
(gdb) n
Catchpoint 3 (forked process 109279), 0x00007ffff7ac67cc in __libc_fork () at ../sysdeps/nptl/fork.c:135
135 in ../sysdeps/nptl/fork.c
(gdb)
[New process 109279]
Reading symbols from GDB_debug/multiprocess_demo...done.
Reading symbols from /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.27.so...done.
Reading symbols from /usr/lib/debug/lib/x86_64-linux-gnu/ld-2.27.so...done.
__libc_fork () at ../sysdeps/nptl/fork.c:142
142 ../sysdeps/nptl/fork.c: No such file or directory.
(gdb) info inferiorsNum Description Executable1 process 109275 GDB_debug/multiprocess_demo
* 2 process 109279 GDB_debug/multiprocess_demo
(gdb) n
main () at multiprocess_demo.c:8
8 if (pid1 0) {
(gdb)
10 printf(Child Process 1 (PID: %d)\n, getpid());
(gdb) n
Child Process 1 (PID: 109279)
28 return 0;
(gdb) n
29 }
(gdb) n
[Inferior 2 (process 109279) exited normally]
(gdb) n
The program is not being run.
(gdb) info inferiorsNum Description Executable1 process 109275 GDB_debug/multiprocess_demo
* 2 null GDB_debug/multiprocess_demo
(gdb) inferior 1
[Switching to inferior 1 [process 109275] (GDB_debug/multiprocess_demo)]
[Switching to thread 1.1 (process 109275)]
#0 0x00007ffff7ac67cc in __libc_fork () at ../sysdeps/nptl/fork.c:135
135 ../sysdeps/nptl/fork.c: No such file or directory.
(gdb) n
main () at multiprocess_demo.c:8
8 if (pid1 0) {
(gdb)
13 pid2 fork();
(gdb) n
(gdb)
[New process 109280]
Reading symbols from GDB_debug/multiprocess_demo...done.
Reading symbols from /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.27.so...done.
Reading symbols from /usr/lib/debug/lib/x86_64-linux-gnu/ld-2.27.so...done.
__libc_fork () at ../sysdeps/nptl/fork.c:142
142 ../sysdeps/nptl/fork.c: No such file or directory.(gdb)
main () at multiprocess_demo.c:14
14 if (pid2 0) {
(gdb)
16 printf(Child Process 2 (PID: %d)\n, getpid());
(gdb)
Child Process 2 (PID: 109280)
28 return 0;
(gdb)
29 }
(gdb)
[Inferior 3 (process 109280) exited normally]
(gdb) info inferiorsNum Description Executable1 process 109275 GDB_debug/multiprocess_demo* 3 null GDB_debug/multiprocess_demo
(gdb) n
The program is not being run.
(gdb) info inferiorsNum Description Executable1 process 109275 GDB_debug/multiprocess_demo* 3 null GDB_debug/multiprocess_demo
(gdb) continue
The program is not being run.
(gdb) n
The program is not being run.
(gdb) info inferiorsNum Description Executable1 process 109275 GDB_debug/multiprocess_demo* 3 null GDB_debug/multiprocess_demo
(gdb) inferior 1
[Switching to inferior 1 [process 109275] (GDB_debug/multiprocess_demo)]
[Switching to thread 1.1 (process 109275)]
#0 0x00007ffff7ac67cc in __libc_fork () at ../sysdeps/nptl/fork.c:135
135 ../sysdeps/nptl/fork.c: No such file or directory.
main () at multiprocess_demo.c:14
14 if (pid2 0) {
(gdb)
20 printf(Parent Process (PID: %d)\n, getpid());
(gdb)
Parent Process (PID: 109275)
23 waitpid(pid1, NULL, 0);
(gdb) n
24 waitpid(pid2, NULL, 0);
(gdb) n
28 return 0;
(gdb) info inferiorsNum Description Executable* 1 process 109275 GDB_debug/multiprocess_demo
(gdb) n
29 }
(gdb) n
[Inferior 1 (process 109275) exited normally]
(gdb) n
The program is not being run.如下是对上面的进行的备注
再次逻辑与命令说明
set follow-fork-mode childfork后跟踪子进程set detach-on-fork off不自动分离调试器break fork 设置断点在 fork() 处catch fork 在 fork() 处停下并切换到子进程continue 继续执行这将在子进程中停下info inferiors 查看当前进程inferiors 2 切换到指定进程例如第二个进程
这样就可以单独的调试某个进程了
gdb sever的连接调试
在这里我简单说明下连接的三个基本流程流程
在目标机器上启动 GDB Servergdbserver :1234 /path/to/your/target/program在本地机器上启动 GDB 并连接到 GDB Servergdb /path/to/your/target/program在 GDB 中连接到 GDB Servertarget remote target_system_ip:1234在本地 GDB 中进行调试
这个内容的实操我会在后面的文档中体现出来一篇文档内容过多比较冗余
对于前面的GDB的8个作用基本就覆盖了还差一个core dump的就让读者自己完成吧主要就是做一个抛砖引玉的作用嘻嘻
