[Buildroot] [PATCH 03/34] reproducibility: generate SOURCE_DATE_EPOCH

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Tue, May 10, 2016 at 01:28:14AM +0200, Arnout Vandecappelle wrote:
> On 05/08/16 22:22, Gilles Chanteperdrix wrote:
> > On Sat, May 07, 2016 at 11:00:11PM +0200, Arnout Vandecappelle wrote:
> >> On 04/30/16 09:48, Gilles Chanteperdrix wrote:
> >>> When reproducibility is wanted, generates a global SOURCE_DATE_EPOCH
> >>> environment variable which contains either the date of buildroot last
> >>> commit if running from a git repository, or the latest release date.
> >>>
> >>> This means that all packages embedding build dates will appear to
> >>> have the same build date, so in case of new commit or release, all
> >>> packages will appear to have been change, even though some of them
> >>> may not have changed in fact.
> >>> ---
> >>>  Makefile | 5 +++++
> >>>  1 file changed, 5 insertions(+)
> >>>
> >>> diff --git a/Makefile b/Makefile
> >>> index 86b2ed2..c1d2961 100644
> >>> --- a/Makefile
> >>> +++ b/Makefile
> >>> @@ -223,6 +223,11 @@ ifeq ($(BR2_REPRODUCIBLE),y)
> >>>  export TZ=UTC
> >>>  export LANG=C
> >>>  export LC_ALL=C
> >>> +SOURCE_DATE_GIT = $(shell GIT_DIR=$(TOPDIR)/.git $(GIT) log -1 --format=%at)
> >>> +SOURCE_DATE_CHANGES = $(shell head -n 1 $(TOPDIR)/CHANGES | \
> >>> +	sed 's/^.*Released \(.*\)$$/\1/;s/\(st\|nd\|rd\|th\),//' | \
> >>> +	LANG=C LC_ALL=C TZ=UTC xargs -i date -d \{\} +%s)
> >>> +export SOURCE_DATE_EPOCH = $(if $(wildcard $(TOPDIR)/.git),$(SOURCE_DATE_GIT),$(SOURCE_DATE_CHANGES))
> >>
> >>   I really don't like exporting a variable that is not well-known and that
> >> doesn't have a BR_ prefix. Where it is used by packages, it will anyway be in
> >> Buildroot-specific patches, so we can just as well add the BR_ prefix.
> >
> > SOURCE_DATE_EPOCH is well-known. Its meaning is defined by a
> > specification:
> > https://wiki.debian.org/ReproducibleBuilds/TimestampsProposal
> 
>   Ah, good.
> 
>   Actually, a better reference is
> https://reproducible-builds.org/specs/source-date-epoch/
> (actually the same developers wrote this spec, but it's supposedly not 
> debian-specific).
> 
>   When you repost, could you make sure that the commit message mentions this 
> explicitly?
> 
> >
> >>
> >>   But actually, we don't want to introduce buildroot-specific (and therefore
> >> unupstreamable) things in patches either. So there is not much point in
> >> exporting, except if it's used by scripts.
> >
> > I used it in some patched configure scripts (libnspr, if I remember
> > correctly). Which is why I exported it.
> 
>   As I said: used in patches.
> 
>   But indeed, it is well-known. So OK to export it.
> 
>   BTW, when it is possible to download a debian patch for a package (by setting 
> FOO_PATCH = ...) rather than rolling our own, we prefer that.

The thing is that trying and understanding what Debian does is not
convenient for me and most of the time a waste of time:
- things that I believe are problems for buildroot may not be
considered problems for Debian (see for instance the libltdl issue,
or the grub2 issue). 
- the Debian wiki has a high noise/signal ratio, and is not always
up to date, and this when I can access it, because the IP addresses
I use for browsing are blacklisted by Debian, so I have to take
special steps to access it.

So, I gave up on Debian pretty early, and I am not interested in
trying that painful exercise again. If someone else wants to do it
though, go ahead.

-- 
					    Gilles.
https://click-hack.org