Where is ptrace in linux kernel?

Question

I can't find it in kernel source with global ptrace, there is no definition in kernel/ptrace.c like it was stated in man page..... I can see kernel/ptrace.c and include/linux/ptrace.h but there is nothing

Answer 1

You need to look for it in your libc source code, for example glibc or musl. And notice what does it say in man ptrace under NOTES section:

Although arguments to ptrace() are interpreted according to the prototype given, glibc currently declares ptrace() as a variadic function with only the request argument fixed. It is recommended to always supply four arguments, even if the requested operation does not use them, setting unused/ignored arguments to 0L or (void *) 0.

In glibc for example ptrace() is defined in sysdeps/unix/sysv/linux/ptrace.c:

long int
ptrace (enum __ptrace_request request, ...)
{
  long int res, ret;
  va_list ap;
  pid_t pid;
  void *addr, *data;

  va_start (ap, request);
  pid = va_arg (ap, pid_t);
  addr = va_arg (ap, void *);
  data = va_arg (ap, void *);
  va_end (ap);

  if (request > 0 && request < 4)
    data = &ret;

  res = INLINE_SYSCALL (ptrace, 4, request, pid, addr, data);
  if (res >= 0 && request > 0 && request < 4)
    {
      __set_errno (0);
      return ret;
    }

  return res;
}