Re: Combine AR support with autodependencies

[Paul Smith]

On Wed, 2016-07-20 at 11:36 -0700, jandyman wrote:
> Does anyone have an example of this, or can explain a little better
> how the archive support works under the hood? As mentioned above the
> GNU manual is rather unclear in this section.

I don't quite know what you're trying to do or what information you're
looking for: usually a very abstract question like this is hard to
answer.  If you provide a specific, small, runnable example of what you
want to do and describe what fails and what you expected to happen,
it's easier to discuss it.

As far as the internal implementation, GNU make actually has the
ability to directly parse archive files and extract the timestamp
information from them: it doesn't invoke ar to get that information.

One thing to note is that as part of the reproducible build initiative
unfortunately ar is often built these days such that "deterministic
mode" is the default; this means that the timestamp information in the
archive is always zeroed.  I filed a bug about this in Debian,
requesting that the default be restored to "non-deterministic" and the
deterministic build effort make use of some other method to enable
deterministic mode (maybe some kind of environment variable).  However,
no response to that.

If you want to rely on timestamps always add the "U" option to your ar
commands, if you use GNU binutils that you didn't build yourself.