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To: freebsd-hackers@FreeBSD.org
Subject: Weird PT_DETACH
From: Jiangyi Liu <gzjyliu@public.guangzhou.gd.cn>
Date: 30 May 2001 20:45:12 +0800
Message-ID: <878zjf0zvr.fsf@fatcow.home>
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Hi all,

The ptrace(2) man page is probably outdated. I used PT_DETACH in the
following code, but it didn't run ./test. I also tried to use
ptrace(PT_DETACH, pid, (caddr_t)1, 0) to detach, but it failed too.

BTW, if I omit wait(0) and ptrace(PT_DETACH, ...) in the code, after
it runs there is a process sticking to the system. Even kill -9 can't
kill it.

$ ps aux | grep jyliu
...
jyliu    423  0.0  0.1   216  100  p2  TX    7:41AM   0:00.00  (test)
...
$ kill -9 423
$ ps aux | grep jyliu
...
jyliu    423  0.0  0.1   216  100  p2  TX    7:41AM   0:00.00  (test)
...

So it's still there. Quite funny. Any clue?

Jiangyi

---code begins here
#include <unistd.h>
#include <sys/types.h>
#include <sys/ptrace.h>

int main()
{
    pid_t pid;
    
    if(!(pid=fork())) {
        /* child */
        ptrace(PT_TRACE_ME, 0, 0, 0);
        puts("child speaking");
        execve("./test", NULL, NULL);
    } else {
        wait(0);
        ptrace(PT_DETACH, pid, 0, 0);
        exit(0);
    }
}
---code ends here

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