remote debugging gdb multiple process
I am unable to debug a child process of a remote debugging session. I found a similar question How to debug the entry-point of fork-exec process in GDB?
I am following the same procedure, although for a remote target. Is follow-fork-mode child
supported for remote targets ?
Following is my sample code..
1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <sys/types.h>
4 #include <unistd.h>
5
6 int spawn (void)
7 {
8 pid_t child_pid;
9 /* Duplicate this process. */
10 child_pid = fork ();
11 if (child_pid != 0)
12 /* This is the parent process. */
13 return child_pid;
14 else {
15 /* Now execute PROGRAM, searching for it in the path. */
16 while(1)
17 {
18 static int i = 0;
19 if(i==0) /* break here for child */
20 {
21 printf("I am child\n");
22 }
23 else if(i==3)
24 {
25 return 1;
26 }
27 else
28 {
29 i = 0/0;
30 }
31 i++;
32 }
33 }
34 return 0;
35 }
36 int main ()
37 {
38 /* Spawn a child process running the .ls. command. Ignore the
39 returned child process ID. */
40 printf("Hello World..!!\n");
41 spawn ();
42 printf ("Bbye World..!!\n");
43 return 0;
44 }
Running it with gdb, I can set set break point in child.. all fine here.!!
sh-3.2# gdb fork
(gdb) set follow-fork-mode child
(gdb) set 开发者_如何学Pythondetach-on-fork off
(gdb) b 19
Breakpoint 1 at 0x80483d0: file fork-exec.c, line 19.
(gdb) c
The program is not being run.
(gdb) start
Breakpoint 2 at 0x8048437: file fork-exec.c, line 40.
Starting program: fork
main () at fork-exec.c:40
40 printf("Hello World..!!\n");
(gdb) c
Continuing.
Hello World..!!
[Switching to process 10649]
Breakpoint 1, spawn () at fork-exec.c:19
19 if(i==0) /* break here for child */
(gdb)
However if I try to catch child via gdbserver break point is lost..
sh-3.2# gdbserver :1234 fork &
[5] 10686
sh-3.2# Process fork created; pid = 10689
Listening on port 1234
Run as target remote
sh-3.2# gdb fork
(gdb) target remote localhost:1234
Remote debugging using localhost:1234
Remote debugging from host 127.0.0.1
[New Thread 10689]
0x00bd2810 in _start () from /lib/ld-linux.so.2
(gdb) break 19
Breakpoint 1 at 0x80483d0: file fork-exec.c, line 19.
(gdb) c
Continuing.
Hello World..!!
Bbye World..!!
Child exited with retcode = 0
Program exited normally.
Child exited with status 0
GDBserver exiting
What is the procedure to debug child process in embedded world. I know I can do a process attach, but I want to debug from the very beginning of the child process..
It is called follow-fork. No, it is not supported in gdbserver.
As a (dirty!) workaround, you can just add a sleep()
call right after the fork()
with a delay long enough for you to get the child PID, attach it with another instance of gdbserver and connect to it with gdb.
It should work with a modern gdb version, according to this bug-report.
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