It is case specific and involves fingerprinting each built file. For
example, with prelinking you rewrite the elf headers, and to verify
equivalence you simply set the linker instructions to 0 while calculating
the file checksum.

On Mon, Jan 4, 2016, 1:01 AM Tim Barbour <[email protected]> wrote:

> On Sat, 26 Dec 2015 09:07:38 +0000,
> Wout Mertens wrote:
> > If web-of-trust is the best solution, and the only blocker is build
> reproducability, how about trying to classify
> > build differences?
> >
> > Each of the differences will have a reason, and either we can fix the
> build to be deterministic (e.g. timestamps,
> > build paths), or we can classify a class of changes as equivalent (e.g.
> optimalizations resulting in equivalent
> > code, prelinking).
> > [...]
>
> Your suggestion sounds a bit like homotopy, which type theorists are now
> using
> to resolve their long-standing difficulties with intensional vs extensional
> equality; perhaps there is a connection between these difficulties and the
> fact that Nixos is not yet using the intensional Nix store model.
>
> How would one verify that the builds are equivalent, and that the
> difference
> is not due to a malicious modification ?
>
> Tim
>
-- 

Wout.
(typed on mobile, excuse terseness)
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