The parent and child processes call getpid. why cannot the child process be tracked?

The parent and child processes call getpid. why cannot the child process be tracked? -- Linux general technology-Linux programming and kernel information. The following is a detailed description. [I = s] This post was last edited by jipingwt

I wrote a small program (test. c), as follows:
# Include
# Include
# Include
# Include

Int main ()
{
Int I;
Pid_t pid, p;

If (pid = fork () = 0 ){
Sleep (3 );
P = getpid ();
Printf ("% ld \ n", p );
Exit (0 );
}
Else if (pid <0 ){
Printf ("0 error ");
Exit (1 );
}
P = getpid ();
Printf ("% ld \ n", p );
Wait (& I );
Return 0;
}

The pid number of the parent and child processes can be obtained after the compilation, but it is strange that the strace-f tracking program is used to start and the system call of the getpid of the parent process can be tracked, however, the sub-process cannot trace the call to getpid! (As shown below)
Execve ("./test", ["./test"], [/* 43 vars */]) = 0
......
Clone (Process 3858 attached
Child_stack = 0, flags = CLONE_CHILD_CLEARTID | CLONE_CHILD_SETTID | SIGCHLD, child_tidptr = 0xb7fce708) = 3858
[Pid 3857] Getpid () = 1, 3857
[Pid 3857] fstat64 (1, {st_mode = S_IFCHR | 0620, st_rdev = makedev (136, 4),...}) = 0
[Pid 3857] mmap2 (NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS,-1, 0) = 0xb7fe4000
[Pid 3857] write (1, "3857 \ n", 53857
) = 5
[Pid 3857] wait4 (-1, Process 3857 suincluded

[Pid 3858] rt_sigprocmask (SIG_BLOCK, [CHLD], [], 8) = 0
[Pid 3858] rt_sigaction (SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
[Pid 3858] rt_sigprocmask (SIG_SETMASK, [], NULL, 8) = 0
[Pid 3858] nanosleep ({3, 0}, {3, 0}) = 0
[Pid 3858] fstat64 (1, {st_mode = S_IFCHR | 0620, st_rdev = makedev (136, 4),...}) = 0
[Pid 3858] mmap2 (NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS,-1, 0) = 0xb7fe4000
[Pid 3858] write (1, "3858 \ n", 53858
) = 5
[Pid 3858] exit_group (0) =?
Process 3857 resumed
Process 3858 detached
<... Wait4 resumed> [{WIFEXITED (s) & WEXITSTATUS (s) = 0}], 0, NULL) = 3858
--- SIGCHLD (Child exited) @ 0 (0 )---
Exit_group (0) =?

I added the printk statement in sys_getpid () and checked it through dmesg. I found that the parent process was executed, but the child process was not executed. If the sub-process does not seem to execute sys_getpid, how does the sub-process obtain its own pid number?

Please solve this problem!