gdb) list
1 #include <stdio.h>
2 void debug(char *str)
3 {
4 printf("debug info :%s\n",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\n", 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=5Breakpoint 1, main (argc=1, argv=0x7fffffffe548) at e.c:10
10 j+=5;
(gdb) c
Continuing.
now a=10Breakpoint 1, main (argc=1, argv=0x7fffffffe548) at e.c:10
10 j+=5;
(gdb)
使用delete breakpoints 斷點號 刪除斷點 這里的斷點號表示的是第幾個斷點,剛才執行break 10返回 reakpoint 1 at 0x40050a: file e.c, line 10. 中的1表示該斷點的標號，因此使用 delete breakpoints 1表示刪除第10行所定義的斷點 clear n表示清除第n行的斷點,因此clear 10等同于delete breakpoints 1 disable/enable n表示使得編號為n的斷點暫時失效或有效 可使用info查看斷點相關的信息 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 查看參數的值
(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=5Breakpoint 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
step及next命令 step可使得程序逐條執行,即執行完一條語句然后在嚇一跳語句前停下來,等待用戶的命令 一般使用step命令是，可使用display或者watch命令查看變量的變化,從而判斷程序行為是否符合要求 當下一條指令為函數時,s進入函數內部,在其第一條語句前停下來 step n,next n 表示連續但不執行n條指令,如果期間遇到斷點,則停下來
(gdb) list
1 #include <stdio.h>
2 void debug(char *str)
3 {
4 printf("debug info :%s\n",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\n", 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\n", j);
(gdb) s
__printf (format=0x400648 "now j=%d\n") at printf.c:30
30 {
(gdb) bt
#0 __printf (format=0x400648 "now j=%d\n") 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) sBreakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:11
11 j+=5;
(gdb) s
12 printf("now j=%d\n", j);
(gdb) n
now j=10
13 debug("x=======x");
(gdb) n
debug info :x=======x
10 for(i=0;i<10;i++){
(gdb)
(gdb) list
1 #include <stdio.h>
2 void debug(char *str)
3 {
4 printf("debug info :%s\n",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\n", 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: jOld value = 0
New value = 5
main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
(gdb) c
Continuing.
now j=5
debug info :x=======x
Hardware watchpoint 2: jOld value = 5
New value = 10
main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
print命令
(gdb) list
1 #include <stdio.h>
2 void debug(char *str)
3 {
4 printf("debug info :%s\n",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\n", 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\n", j);
(gdb) p j
$1 = 5
(gdb) c
Continuing.
now j=5
debug info :x=======xBreakpoint 1, main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
(gdb) p i,j
$2 = 10
(gdb) p j
$3 = 10
(gdb)
set var name=value 在程序運行中動態改變變量的值
(gdb) list
1 #include <stdio.h>
2 void debug(char *str)
3 {
4 printf("debug info :%s\n",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\n", 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: jOld value = 0
New value = 5
main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
(gdb) c
Continuing.
now j=5
debug info :x=======x
Hardware watchpoint 2: iOld 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: jOld value = 5
New value = 10
main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
(gdb) c
Continuing.
now j=10
debug info :x=======x
Hardware watchpoint 2: iOld 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: jOld value = 10
New value = 15
main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
(gdb) c
Continuing.
now j=15
debug info :x=======x
Hardware watchpoint 2: iOld 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: jOld value = 15
New value = 20
main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
(gdb) c
Continuing.
now j=20
debug info :x=======x
Hardware watchpoint 2: iOld 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: jOld value = 20
New value = 25
main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
(gdb) c
Continuing.
now j=25
debug info :x=======x
Hardware watchpoint 2: iOld 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: jOld value = 25
New value = 30
main (argc=1, argv=0x7fffffffe538) at e.c:12
12 printf("now j=%d\n", j);
(gdb) c
Continuing.
now j=30
debug info :x=======x
Hardware watchpoint 2: iOld 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.
函數調用相關的 backtrace 可使用frame 查看堆棧中某一幀的信息
(gdb) list
1 #include <stdio.h>
2 void debug(char *str)
3 {
4 printf("debug info :%s\n",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\n", 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=5Breakpoint 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\n",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\n") at printf.c:30
30 {
(gdb) bt
#0 __printf (format=0x400638 "debug info :%s\n") 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\n") 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\n", ap=0x7fffffffe330) at vfprintf.c:236
236 int save_errno = errno;
(gdb) bt
#0 _IO_vfprintf_internal (s=0x333a58f040, format=0x400638 "debug info :%s\n", 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=10Breakpoint 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
