трассировка процесса (process trace)
Возвращаемое значение (Return value)
On success, the PTRACE_PEEK* requests return the requested data
(but see NOTES), the PTRACE_SECCOMP_GET_FILTER request returns
the number of instructions in the BPF program, the
PTRACE_GET_SYSCALL_INFO request returns the number of bytes
available to be written by the kernel, and other requests return
zero.
On error, all requests return -1, and errno is set to indicate
the error. Since the value returned by a successful PTRACE_PEEK*
request may be -1, the caller must clear errno before the call,
and then check it afterward to determine whether or not an error
occurred.
