Re: [ptxdist] [PATCH 2/3] barebox: add option for building barebox reproducibly

[Michael Olbrich <m.olbrich@pengutronix.de>]

On Tue, Oct 16, 2018 at 10:57:20AM +0000, Baeuerle, Florian wrote:
> Hi Michael,
> 
> Am Dienstag, den 16.10.2018, 12:09 +0200 schrieb Michael Olbrich:
> > On Thu, Oct 11, 2018 at 02:19:17PM +0000, Baeuerle, Florian wrote:
> > > Inject fake timestamps into the build via faketime to produce the exact
> > > same binaries.
> > 
> > I'd like to see this patch split in two.
> > One to handle the KBUILD_BUILD_ stuff. That should be done like the kernel
> > with the symlink magic, but otherwise unconditionally (for now).
> > Use SOURCE_DATE_EPOCH for the timestamp. I want to change the kernel to use
> > this too.
> 
> SOURCE_DATE_EPOCH uses the ptxdist release number for the timestamp, thus the
> timestamp changes with every ptxdist release. I'd prefer to *really* get the
> same binary when the source code was not changed at all. A ptxdist version bump
> has a high potential of not touching anything barebox related.
> 
> I also do not like mangling the barebox version into a timestamp, but I couldn't
> come up with any better idea.

You can easily overwrite that in your BSP and I'm wouldn't mind changing
that in general. The PTXdist release was just a convenient 'date' to use.
I'd like to have something that is global to the BSP. Do you have any
sugestions?

> > Another patch for the rest. I'm not quite sure how I want to handle this.
> > My current plan is to have a setup option: Developers can use it to disable
> > reproducible builds to see stuff like the build timestamps etc.
> > CI and release builds have it enabled by default. I currently don't have
> > any reason do disable reproducibility for releases.
> > 
> > What do you think?
> 
> My main use case for reproducible builds is RAUC. Since bootloader updates are
> especially hairy on some platforms, I'm happy about having the ability to spare
> a few of them (while retaining an update mechanism that ensures a persistent
> state of the system *and* without using prebuilt bootloaders).
> 
> However, I do not mind if ptxdist by default builds more packages reproducibly.

Updates are certainly one use-case. For me it's also useful to develop
PTXdist. I can compare ipkgs from before and after some refactoring more
easily.

Michael

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