int linux_pid_exe_is_elf_64_file (int pid, unsigned int *machine);
-void linux_attach_lwp (unsigned long pid);
+/* Attach to PTID. Returns 0 on success, non-zero otherwise (an
+ errno). */
+int linux_attach_lwp (ptid_t ptid);
+
+/* Return the reason an attach failed, in string form. ERR is the
+ error returned by linux_attach_lwp (an errno). This string should
+ be copied into a buffer by the client if the string will not be
+ immediately used, or if it must persist. */
+char *linux_attach_fail_reason_string (ptid_t ptid, int err);
+
struct lwp_info *find_lwp_pid (ptid_t ptid);
void linux_stop_lwp (struct lwp_info *lwp);