Why each time of kernel compilation must be done completely?

[greg@kroah.com (Greg KH)]

On Thu, Nov 20, 2014 at 10:05:04AM +0800, ??? wrote:
> Hi,
> 
> This problem has puzzled me for a long time. A normal C make file could parse
> the reliance and just regenerate the modified source file. But each time when I
> modified the kernel and recompile it, it does a complete compilation, no matter
> whether make mrproper is used or not. It's quite time consuming and
> inefficient.
> 
> So why kernel make file couldn't do what a normal C make file could do? Or
> maybe it could but I got something wrong? 

I think you are doing something wrong, unless you are changing a
configuration option, version of gcc, or are changing a .h file that all
files include.

What are you changing and doing that causes a full rebuild?  Can you
show us exactly?

> If a complete compilation is inevitable, how to make it faster? I only know the
> -jX option.

-jX is all you need.  You can use ccache if you are rebuilding the same
thing all the time, or distcc if you have other machines on your network
to take advantage of.

thanks,

greg k-h