Git and ident of binaries

[Curt Sampson <cjs%netbsd.org@localhost>]

On 2010-01-12 17:19 +0000 (Tue), David Holland wrote:

>  > These days, my preference would be to kill [keyword expansion]. It
>  > makes me nervous that a checkout of a particular revision is not
>  > what's in the repository for that particular revision, but instead
>  > a modified copy whose particular modifications may change when the
>  > VCS software changes.
> 
> It is nonetheless desirable to be able to ident binaries.

I agree that that would be nice.

In git, it seems to me that this could be done with a pre-commit hook
which would expand or change the $NetBSD$ tag appropriately just before
commit, thus ensuring that the right thing is in the repository itself.
But I see two issues with this:

    1. We can't use the SHA-1 of the commit in the id because we don't
    know what that SHA-1 is is, and we can't determine the SHA-1 of the
    commit until after we set the id. I suppose we could use the author
    and date, which should be enough to identify the commit.

    2. How do we make sure that everybody's using this hook in their own
    repos? Hooks don't get cloned when you clone a repo.

On the other hand, given that with Git the part of the ids that changes
with the version is no longer a per-file thing but a per-commit thing
(i.e., an entire checkout has the same version), perhaps a better way of
approaching it might be to have the build system insert or expand the
IDs. (It could look up the SHA-1 of the current checkout.)

What do we really want to know when we use ident on a binary to see what
it was built with? The filename of each source file used to build it
(which list is incomplete in our current system--e.g., we don't know the
version of the .h files), and the version of the commit?

cjs
-- 
Curt Sampson         <cjs%cynic.net@localhost>         +81 90 7737 2974
             http://www.starling-software.com
The power of accurate observation is commonly called cynicism
by those who have not got it.    --George Bernard Shaw