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

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

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.

> > 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 :-).

> > 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.

Ian.

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