GDB调试
启动程序准备调试
GDB yourpram
或者
先输入GDB
然后输入 file yourpram
然后使用run或者r命令开始程序的执行,也可以使用 run parameter将参数传递给该程序
参数列表
|
命令 |
命令缩写 |
命令说明 |
|
list |
l |
显示多行源代码 |
|
break |
b |
设置断点,程序运行到断点的位置会停下来 |
|
info |
i |
描述程序的状态 |
|
run |
r |
开始运行程序 |
|
display |
disp |
跟踪查看某个变量,每次停下来都显示它的值 |
|
step |
s |
执行下一条语句,如果该语句为函数调用,则进入函数执行其中的第一条语句 |
|
next |
n |
执行下一条语句,如果该语句为函数调用,不会进入函数内部执行(即不会一步步地调试函数内部语句) |
|
|
p |
打印内部变量值 |
|
continue |
c |
继续程序的运行,直到遇到下一个断点 |
|
set var name=v |
|
设置变量的值 |
|
start |
st |
开始执行程序,在main函数的第一条语句前面停下来 |
|
file |
|
装入需要调试的程序 |
|
kill |
k |
终止正在调试的程序 |
|
watch |
|
监视变量值的变化 |
|
backtrace |
bt |
查看函数调用信息(堆栈) |
|
frame |
f |
查看栈帧 f n 切换到编号为n的栈 |
|
quit |
q |
退出GDB环境 |
//e.c #include <stdio.h> void debug(char *str) { printf("debug info :%s ",str ); } main(int argc,char *argv[]){ int i,j; j=0; for(i=0;i<10;i++){ j+=5; printf("now a=%d ", j); } }
gcc -g -o e e.c
调试gdb e
或者输入gdb
然后 file e
list 命令用法
list命令显示多行源代码,从上次的位置开始显示,默认情况下,一次显示10行,第一次使用时,从代码起始位置显示
gdb) list 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); 5 } 6 main(int argc,char *argv[]){ 7 int i,j; 8 j=0; 9 for(i=0;i<10;i++){ 10 j+=5; (gdb)
list n显示已第n行未中心的10行代码
(gdb) list 8 3 { 4 printf("debug info :%s ",str ); 5 } 6 main(int argc,char *argv[]){ 7 int i,j; 8 j=0; 9 for(i=0;i<10;i++){ 10 j+=5; 11 printf("now a=%d ", j); 12 } (gdb)
list functionname显示以functionname的函数为中心的10行代码
(gdb) list main 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); 5 } 6 main(int argc,char *argv[]){ 7 int i,j; 8 j=0; 9 for(i=0;i<10;i++){ 10 j+=5; (gdb)
list - 显示刚才打印过的源代码之前的代码
(gdb) list 10 5 } 6 main(int argc,char *argv[]){ 7 int i,j; 8 j=0; 9 for(i=0;i<10;i++){ 10 j+=5; 11 printf("now a=%d ", j); 12 } 13 }(gdb) list - 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); (gdb)
断点命令break
break location:在location位置设置断点,该位置可以为某一行,某函数名或者其它结构的地址
GDB会在执行该位置的代码之前停下来
gdb) list 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); 5 } 6 main(int argc,char *argv[]){ 7 int i,j; 8 j=0; 9 for(i=0;i<10;i++){ 10 j+=5; (gdb) 11 printf("now a=%d ", j); 12 } 13 }(gdb) break 10 Breakpoint 1 at 0x40050a: file e.c, line 10. (gdb) r Starting program: /mnt/hgfs/www/c/gcc/e Breakpoint 1, main (argc=1, argv=0x7fffffffe548) at e.c:10 10 j+=5; (gdb) c Continuing. now a=5 Breakpoint 1, main (argc=1, argv=0x7fffffffe548) at e.c:10 10 j+=5; (gdb) c Continuing. now a=10 Breakpoint 1, main (argc=1, argv=0x7fffffffe548) at e.c:10 10 j+=5; (gdb)
使用delete breakpoints 断点号 删除断点
这里的断点号表示的是第几个断点,刚才执行break 10返回 reakpoint 1 at 0x40050a: file e.c, line 10.
中的1表示该断点的标号，因此使用 delete breakpoints 1表示删除第10行所定义的断点
clear n表示清除第n行的断点,因此clear 10等同于delete breakpoints 1
disable/enable n表示使得编号为n的断点暂时失效或有效
可使用info查看断点相关的信息
info breakpoints
gdb) info breakpoints No breakpoints or watchpoints. (gdb) break 10 Breakpoint 2 at 0x40050a: file e.c, line 10. (gdb) break 9 Breakpoint 3 at 0x400501: file e.c, line 9. (gdb) info breakpoints Num Type Disp Enb Address What 2 breakpoint keep y 0x000000000040050a in main at e.c:10 3 breakpoint keep y 0x0000000000400501 in main at e.c:9
display命令
查看参数的值
(gdb) break 10 Breakpoint 1 at 0x40050a: file e.c, line 10. (gdb) r Starting program: /mnt/hgfs/www/c/gcc/e Breakpoint 1, main (argc=1, argv=0x7fffffffe548) at e.c:10 10 j+=5; (gdb) display j 1: j = 0 (gdb) c Continuing. now a=5 Breakpoint 1, main (argc=1, argv=0x7fffffffe548) at e.c:10 10 j+=5; 1: j = 5 (gdb) display 1: j = 5 (gdb) display i 2: i = 1 (gdb) display j 3: j = 5 (gdb) display j*2 4: j*2 = 10 (gdb) info display Auto-display expressions now in effect: Num Enb Expression 4: y j*2 3: y j 2: y i 1: y j
也可以使用disable,enable,delete,info命令修改及查看其状态,用法与对断点的一样
step及next命令
step可使得程序逐条执行,即执行完一条语句然后在吓一跳语句前停下来,等待用户的命令
一般使用step命令是，可使用display或者watch命令查看变量的变化,从而判断程序行为是否符合要求
当下一条指令为函数时,s进入函数内部,在其第一条语句前停下来
step n,next n 表示连续但不执行n条指令,如果期间遇到断点,则停下来
(gdb) list 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); 5 } 6 7 main(int argc,char *argv[]){ 8 int i,j; 9 j=0; 10 for(i=0;i<10;i++){ (gdb) 11 j+=5; 12 printf("now j=%d ", j); 13 debug("x=======x"); 14 } 15 }(gdb) Line number 16 out of range; e.c has 15 lines. (gdb) break 11 Breakpoint 1 at 0x40050a: file e.c, line 11. (gdb) r Starting program: /mnt/hgfs/www/c/gcc/e1 Breakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:11 11 j+=5; (gdb) s 12 printf("now j=%d ", j); (gdb) s __printf (format=0x400648 "now j=%d ") at printf.c:30 30 { (gdb) bt #0 __printf (format=0x400648 "now j=%d ") at printf.c:30 #1 0x0000000000400525 in main (argc=1, argv=0x7fffffffe538) at e.c:12 (gdb) n 34 va_start (arg, format); (gdb) n 35 done = vfprintf (stdout, format, arg); (gdb) n now j=5 39 } (gdb) bt #0 __printf (format=<value optimized out>) at printf.c:39 #1 0x0000000000400525 in main (argc=1, argv=0x7fffffffe538) at e.c:12 (gdb) n main (argc=1, argv=0x7fffffffe538) at e.c:13 13 debug("x=======x"); (gdb) n debug info :x=======x 10 for(i=0;i<10;i++){ (gdb) s Breakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:11 11 j+=5; (gdb) s 12 printf("now j=%d ", j); (gdb) n now j=10 13 debug("x=======x"); (gdb) n debug info :x=======x 10 for(i=0;i<10;i++){ (gdb)
watch
watch可设置观察点(watchpoint)。使用观察点可以使得当某表达式的值发生变化时,程序暂停执行。
执行该命令前，必须保证程序已经运行
(gdb) list 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); 5 } 6 7 main(int argc,char *argv[]){ 8 int i,j; 9 j=0; 10 for(i=0;i<10;i++){ (gdb) 11 j+=5; 12 printf("now j=%d ", j); 13 debug("x=======x"); 14 } 15 }(gdb) Line number 16 out of range; e.c has 15 lines. (gdb) b main Breakpoint 1 at 0x4004fa: file e.c, line 9. (gdb) r Starting program: /mnt/hgfs/www/c/gcc/e1 Breakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:9 9 j=0; (gdb) watch j Hardware watchpoint 2: j (gdb) c Continuing. Hardware watchpoint 2: j Old value = 0 New value = 5 main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) c Continuing. now j=5 debug info :x=======x Hardware watchpoint 2: j Old value = 5 New value = 10 main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j);
print命令
(gdb) list 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); 5 } 6 7 main(int argc,char *argv[]){ 8 int i,j; 9 j=0; 10 for(i=0;i<10;i++){ (gdb) 11 j+=5; 12 printf("now j=%d ", j); 13 debug("x=======x"); 14 } 15 }(gdb) Line number 16 out of range; e.c has 15 lines. (gdb) break 12 Breakpoint 1 at 0x40050e: file e.c, line 12. (gdb) r Starting program: /mnt/hgfs/www/c/gcc/e1 Breakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) p j $1 = 5 (gdb) c Continuing. now j=5 debug info :x=======x Breakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) p i,j $2 = 10 (gdb) p j $3 = 10 (gdb)
set var name=value
set args 可指定运行时参数(当main函数需要参数时 如:set args 10 20 30 40 50)
show args 命令可以查看设置好的运行参数
在程序运行中动态改变变量的值
(gdb) list 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); 5 } 6 7 main(int argc,char *argv[]){ 8 int i,j; 9 j=0; 10 for(i=0;i<10;i++){ (gdb) 11 j+=5; 12 printf("now j=%d ", j); 13 debug("x=======x"); 14 } 15 }(gdb) Line number 16 out of range; e.c has 15 lines. (gdb) break main Breakpoint 1 at 0x4004fa: file e.c, line 9. (gdb) r Starting program: /mnt/hgfs/www/c/gcc/e1 Breakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:9 9 j=0; (gdb) watch i Hardware watchpoint 2: i (gdb) watch j Hardware watchpoint 3: j (gdb) c Continuing. Hardware watchpoint 3: j Old value = 0 New value = 5 main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) c Continuing. now j=5 debug info :x=======x Hardware watchpoint 2: i Old value = 0 New value = 1 0x0000000000400533 in main (argc=1, argv=0x7fffffffe538) at e.c:10 10 for(i=0;i<10;i++){ (gdb) c Continuing. Hardware watchpoint 3: j Old value = 5 New value = 10 main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) c Continuing. now j=10 debug info :x=======x Hardware watchpoint 2: i Old value = 1 New value = 2 0x0000000000400533 in main (argc=1, argv=0x7fffffffe538) at e.c:10 10 for(i=0;i<10;i++){ (gdb) c Continuing. Hardware watchpoint 3: j Old value = 10 New value = 15 main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) c Continuing. now j=15 debug info :x=======x Hardware watchpoint 2: i Old value = 2 New value = 3 0x0000000000400533 in main (argc=1, argv=0x7fffffffe538) at e.c:10 10 for(i=0;i<10;i++){ (gdb) c Continuing. Hardware watchpoint 3: j Old value = 15 New value = 20 main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) c Continuing. now j=20 debug info :x=======x Hardware watchpoint 2: i Old value = 3 New value = 4 0x0000000000400533 in main (argc=1, argv=0x7fffffffe538) at e.c:10 10 for(i=0;i<10;i++){ (gdb) set var i=8 (gdb) c Continuing. Hardware watchpoint 3: j Old value = 20 New value = 25 main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) c Continuing. now j=25 debug info :x=======x Hardware watchpoint 2: i Old value = 8 New value = 9 0x0000000000400533 in main (argc=1, argv=0x7fffffffe538) at e.c:10 10 for(i=0;i<10;i++){ (gdb) c Continuing. Hardware watchpoint 3: j Old value = 25 New value = 30 main (argc=1, argv=0x7fffffffe538) at e.c:12 12 printf("now j=%d ", j); (gdb) c Continuing. now j=30 debug info :x=======x Hardware watchpoint 2: i Old value = 9 New value = 10 0x0000000000400533 in main (argc=1, argv=0x7fffffffe538) at e.c:10 10 for(i=0;i<10;i++){ (gdb) c Continuing. Watchpoint 2 deleted because the program has left the block in which its expression is valid. Watchpoint 3 deleted because the program has left the block in which its expression is valid. __libc_start_main (main=0x4004eb <main>, argc=1, ubp_av=0x7fffffffe538, init=<value optimized out>, fini=<value optimized out>, rtld_fini=<value optimized out>, stack_end=0x7fffffffe528) at libc-start.c:258 258 exit (result); (gdb) c Continuing. Program exited with code 026.
函数调用相关的
backtrace
可使用frame 查看堆栈中某一帧的信息
(gdb) list 1 #include <stdio.h> 2 void debug(char *str) 3 { 4 printf("debug info :%s ",str ); 5 } 6 7 main(int argc,char *argv[]){ 8 int i,j; 9 j=0; 10 for(i=0;i<10;i++){ (gdb) 11 j+=5; 12 printf("now j=%d ", j); 13 debug("x=======x"); 14 } 15 }(gdb) Line number 16 out of range; e.c has 15 lines. (gdb) b 13 Breakpoint 1 at 0x400525: file e.c, line 13. (gdb) r Starting program: /mnt/hgfs/www/c/gcc/e1 now j=5 Breakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:13 13 debug("x=======x"); (gdb) s debug (str=0x400652 "x=======x") at e.c:4 4 printf("debug info :%s ",str ); (gdb) bt #0 debug (str=0x400652 "x=======x") at e.c:4 #1 0x000000000040052f in main (argc=1, argv=0x7fffffffe538) at e.c:13 (gdb) s __printf (format=0x400638 "debug info :%s ") at printf.c:30 30 { (gdb) bt #0 __printf (format=0x400638 "debug info :%s ") at printf.c:30 #1 0x00000000004004e9 in debug (str=0x400652 "x=======x") at e.c:4 #2 0x000000000040052f in main (argc=1, argv=0x7fffffffe538) at e.c:13 (gdb) s 34 va_start (arg, format); (gdb) bt #0 __printf (format=0x400638 "debug info :%s ") at printf.c:34 #1 0x00000000004004e9 in debug (str=0x400652 "x=======x") at e.c:4 #2 0x000000000040052f in main (argc=1, argv=0x7fffffffe538) at e.c:13 (gdb) s 35 done = vfprintf (stdout, format, arg); (gdb) s _IO_vfprintf_internal (s=0x333a58f040, format=0x400638 "debug info :%s ", ap=0x7fffffffe330) at vfprintf.c:236 236 int save_errno = errno; (gdb) bt #0 _IO_vfprintf_internal (s=0x333a58f040, format=0x400638 "debug info :%s ", ap=0x7fffffffe330) at vfprintf.c:236 #1 0x000000333a24effa in __printf (format=<value optimized out>) at printf.c:35 #2 0x00000000004004e9 in debug (str=0x400652 "x=======x") at e.c:4 #3 0x000000000040052f in main (argc=1, argv=0x7fffffffe538) at e.c:13 (gdb) c Continuing. debug info :x=======x now j=10 Breakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:13 13 debug("x=======x"); (gdb) bt #0 main (argc=1, argv=0x7fffffffe538) at e.c:13
GDB段错误调试
所谓段错误就是对内存的非法访问
采用GDB调试段错误有2种方法
1.在GDB中运行目标程序,当发生段错误时,GDB中运行的程序会自动停下来
2.直接运行目标程序,使其在发生段错误时产生内存转储(core dump)文件,GDB对该文件进行调试
abort.c
#include <stdio.h> #include <stdlib.h> void recurse(void) { static int i; if( ++i == 3) abort(); else recurse(); } int main(int argc,char ** argv){ recurse(); }
gcc -g -o abort abort.c 使用gdb调试 Line number 15 out of range; abort.c has 14 lines. (gdb) r Starting program: /mnt/hgfs/www/c/gcc/abort Program received signal SIGABRT, Aborted. 0x000000333a232495 in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64 64 return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig); (gdb) bt #0 0x000000333a232495 in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64 #1 0x000000333a233c75 in abort () at abort.c:92 #2 0x00000000004004e7 in recurse () at abort.c:8 #3 0x00000000004004ec in recurse () at abort.c:10 #4 0x00000000004004ec in recurse () at abort.c:10 #5 0x0000000000400502 in main (argc=1, argv=0x7fffffffe528) at abort.c:13 显示在recurse函数调用了3次后调用了abort函数,产生段错误
使用内存转储文件
ulimit -a
[root@centos1 gcc]# ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 7331 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 7331 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited core file size 此时是0
ulimit -c unlimited 设置为不受限制
执行 ./abort 产生内存转储文件
ls 可看到一个名为core且以进程号为后缀的文件
core.6289
gdb abort core.6289
bt
方法同上一个gdb调试