create or replace procedure fetch_ids(ename in varchar2,hiredate in date)
as
begin
select * from emp where empname=ename and join_date=hiredate ;

end;

You've got a few choices:

1. Test the parameters and run a custom SQL statement based on this

if ename is null then
  select * from emp;
else
  select * from emp where empname=ename and join_date=hiredate ;
end if;

2. Have or conditions based on whether ename is null:

select * from emp 
where ( ename is not null and join_date=hiredate and empname=ename ) or
      ( ename is null) ;

3. Dynamic SQL

execute immediate 'select * from emp ' || 
  case when ename is not null then
    'where empname=:ename and join_date=:hiredate'
  else 
    'where :ename is null and nvl(:hiredate, sysdate) is not null'
  end  
  using ename, hiredate

For a simple case like this, I tend towards option 1. As they're separate statements, you'll likely get better plans than option 2. And static SQL is more secure and better code analysis options than dynamic SQL, making it better than 3.