How to compile the kernel identical to the vanilla one?

To: tech-kern%netbsd.org@localhost

Subject: How to compile the kernel identical to the vanilla one?

From: Edwina Ng <edwinang68%gmail.com@localhost>

Date: Thu, 25 Jul 2013 11:02:42 +0800

Hi,

I have extracted the configuration of /netbsd after a vanilla installation with config(1), then untar the syssrc.tgz from source/sets and build the kernel. The file netbsd generated in the build directory is not the same file size as the one in the root directory.

I save the kernel that I have built, delete the build directory and started again afresh. The resultant netbsd has the same file size of the previous one yet, cmp(1) says there are some different.

So my question is, given the same source, same kernel config file, same tool chain and same platform, is that possible for two systems to produce identical compiled kernel images? If not, what is the reason? If yes, which step did I miss?

thanks,