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From:	Achim Gratz <Stromeko AT nexgo DOT de>
To:	cygwin AT cygwin DOT com
Subject:	Re: Deterministic builds
References:	<ff5f5b20-33e2-ef2d-012a-a9e02903ba21 AT cornell DOT edu>
Date:	Wed, 04 May 2016 19:11:20 +0200
In-Reply-To:	<ff5f5b20-33e2-ef2d-012a-a9e02903ba21@cornell.edu> (Ken Brown's message of "Wed, 4 May 2016 09:38:39 -0400")
Message-ID:	<87r3dhbvev.fsf@Rainer.invalid>
User-Agent:	Gnus/5.13 (Gnus v5.13) Emacs/25.0.93 (gnu/linux)
MIME-Version:	1.0

Ken Brown writes:
> Is it possible to build an executable on Cygwin so that subsequent
> builds (with no change in source) produce identical results?
> Currently, the timestamp embedded in executables prevents this.  (I
> don't know if that's the only obstacle.)

I think the basic problems and solutions could be sussed from the work
of Debian folks on reproducible builds:

https://wiki.debian.org/ReproducibleBuilds

> My actual use case is that I'm building a package that produces a
> large number of executables.  If I make a change in one source file,
> I'd like to be able to know which executables change.

Just looking at executables, you will probably find that in gcc there
are a few optimizations that do not produce the same bits on each
compile (depending on available memory, CPU speed or some random seed).
For some of these there are switches to stabilize the result at least.
Timestamps in various file formats are another source of chatter,
although you might be able to either fix thetime or just ignore those
timestamps during comparison (but that's generally more costly than just
doing a plain comparison).


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Wavetables for the Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables

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