Re: [Xen-devel] [PATCH v2 1/8] xen: calculate XEN_BUILD_TIME using XEN_BUILD_DATE value

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Wed, Jul 04, 2018 at 05:30:54PM +0100, Ian Jackson wrote:
> Daniel Kiper writes ("Re: [PATCH v2 1/8] xen: calculate XEN_BUILD_TIME using 
> XEN_BUILD_DATE value"):
> > On Wed, Jul 04, 2018 at 04:41:30PM +0100, Ian Jackson wrote:
> > > I don't have a FreeBSD host to hand to test, CC'ing Roger.
> >
> > This is not the date command problem. This is more related to 
> > SOURCE_DATE_EPOCH
> > spec (https://reproducible-builds.org/specs/source-date-epoch/#idm55)
> > which clearly says:
> >
> >   The value MUST be reproducible (deterministic) across different
> >   executions of the build, depending only on the source code. It SHOULD
> >   be set to the last modification time of the source, incorporating any
> >   packaging-specific modifications.
> >
> > So, AIUI, above implies that we should not use the date command. Am I right?
>
> No.
>
> That spec is for people *setting* SOURCE_DATE_EPOCH.  Which we are not
> doing.
>
> For a *consumer* of SOURCE_DATE_EPOCH, if it is not set, using the
> output of date or the current time or something is fine.

Ahhh... OK, make sens then.

> > > How do in intend to choose which wrapper script to use ?
> >
> > I though that a mechanism to differentiate GNU and BSD systems exists in
> > the Xen build system. So, I was going to reuse it somehow.
>
> ISTR this being slightly clumsy.  But good luck :-).

Thanks a lot! :-)))

> > > This pile of stuff will run on awful lot of times during each make so
> > > keeping it of reasonable size is a good plan.
> > >
> > > Maybe it would be better to have a single shell script which outputs a
> > > whole bunch of variable settings for make to $(eval ) ?
> >
> > It looks that this variable is referenced once, so, it should not be a 
> > problem.
>
> I think make's recursive expansion system may result in these shell
> runes being executed multiple times.

I will double check it.

Daniel

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