On Montag, 21. Dezember 2020 10:01:14 CET Jan Beulich wrote:
> On 18.12.2020 21:42, Maximilian Engelhardt wrote:
> > --- a/docs/Makefile
> > +++ b/docs/Makefile
> > @@ -3,7 +3,13 @@ include $(XEN_ROOT)/Config.mk
> > 
> >  -include $(XEN_ROOT)/config/Docs.mk
> >  
> >  VERSION		:= $(shell $(MAKE) -C $(XEN_ROOT)/xen --no-print-directory
> >  xenversion)> 
> > -DATE		:= $(shell date +%Y-%m-%d)
> > +
> > +DATE_FMT	:= +%Y-%m-%d
> > +ifdef SOURCE_DATE_EPOCH
> > +DATE		:= $(shell date -u -d "@$(SOURCE_DATE_EPOCH)" "$(DATE_FMT)"
> > 2>/dev/null || date -u -r "$(SOURCE_DATE_EPOCH)" "$(DATE_FMT)"
> > 2>/dev/null || date -u "$(DATE_FMT)")
> Looking at the doc for a (deliberately) old "date", I can't find
> any mention of the -d "@..." syntax. I take it the command would
> fail on that system. It would then go on to try the -r variant,
> which has entirely different meaning on GNU (Linux) systems.
> 
> docs/ being subject to configuring, why don't you determine the
> capabilities of "date" there and invoke just the one command
> that was found suitable for the system?
> 
> Jan

Hi Jan,

I did some research. The -d "@..." syntax was introduced about 2005. Testing a 
live CD from 2006 (KNOPPIX_V5.0.1CD-2006-06-01-EN.iso) it was supported there. 
The documentation about this syntax has only been added in 2011 to the date 
command. I'm wondering if anybody running such an old system wants to use 
SOURCE_DATE_EPOCH.

However, I came up with a patch to determine which suitable date version is 
available and only call that, as you suggested. I will post the new patch 
soon.

Maxi