bug#20272: Support reproducible builds

[Vagrant Cascadian]

On 2020-10-08, Maxim Cournoyer wrote:
> I've hit a .go non-reproducibility issue fairly trivially on
> core-updates.  I think it sufficed to change a core library file (e.g.,
> commit 7102c18678dc02d5ee6c77a9a70ae344482af841 which touched (guix
> build utils)) and then attempting to build something with --rounds=2
> flagged it:
>
> --8<---------------cut here---------------start------------->8---
> ./pre-inst-env guix build --rounds=2 mit-krb5 -K --no-substitutes
>
> building 
> /gnu/store/74fh18318l4f9zmkl3y3klyasnc1jqc2-module-import-compiled.drv...
> building 
> /gnu/store/40wzfd27s4i50rc1q86dqks986ff8fq2-module-import-compiled.drv...
> building 
> /gnu/store/dlzy98gvyddjg3zrv5f1l3nvgjvaxjmf-module-import-compiled.drv...
> building 
> /gnu/store/0i3sqm9cl2rbbikfas2y28wibnmqr1pa-module-import-compiled.drv...
> [ 1/ 2] Loading './guix/build/utils.scm'...
> [ 2/ 2] Compiling './guix/build/utils.scm'...
> building 
> /gnu/store/dlzy98gvyddjg3zrv5f1l3nvgjvaxjmf-module-import-compiled.drv...
> building 
> /gnu/store/40wzfd27s4i50rc1q86dqks986ff8fq2-module-import-compiled.drv...
> output ‘/gnu/store/czbmygd6id8qk3bfb0rcjjkmpn5bh7f1-module-import-compiled’ 
> of ‘/gnu/store/dlzy98gvyddjg3zrv5f1l3nvgjvaxjmf-module-import-compiled.drv’ 
> differs from 
> ‘/gnu/store/czbmygd6id8qk3bfb0rcjjkmpn5bh7f1-module-import-compiled-check’ 
> from previous round
> build of 
> /gnu/store/dlzy98gvyddjg3zrv5f1l3nvgjvaxjmf-module-import-compiled.drv failed
> View build log at 
> '/var/log/guix/drvs/dl/zy98gvyddjg3zrv5f1l3nvgjvaxjmf-module-import-compiled.drv.bz2'.
> --8<---------------cut here---------------end--------------->8---

I'm not *positive* this is the same issue, but disabling parallelism
building the Debian package of guix appears to fix reproducibility of
almost all of the .go files... (the one exception is gnu/ci.go embeds
the build path, and just filed a bug for that: #44835)

https://tests.reproducible-builds.org/debian/rb-pkg/experimental/i386/diffoscope-results/guix.html

Notice the somewhat arbitrary list of different gnu/packages/*.scm files
and arbitrary order:

./usr/lib/i386-linux-gnu/guile/3.0/site-ccache/gnu/packages/admin.go

strings --all --bytes=8 {}
Offset 1402, 20 lines modified  Offset 1402, 20 lines modified
1402    -4AI[4-AI[-4AI[ 1402    -4AI[4-AI[-4AI[
1403    Guile·3.0.4                     1403    Guile·3.0.4
1404    arguments                           1404        arguments
1405    native-inputs                   1405    native-inputs
1406    propagated-inputs                   1406        propagated-inputs
1407    sunxi-tools-source                  1407        sunxi-tools-source
1408    gnu/packages/admin.scm          1408    gnu/packages/admin.scm
                                        1409    gnu/packages/aidc.scm
1409    gnu/packages/algebra.scm        1410    gnu/packages/algebra.scm
1410    gnu/packages/anthy.scm          1411    gnu/packages/anthy.scm
1411    gnu/packages/android.scm        1412    gnu/packages/android.scm
1412    gnu/packages/animation.scm       
1413    gnu/packages/aidc.scm    
1414    gnu/packages/agda.scm           1413    gnu/packages/agda.scm
                                        1414    gnu/packages/adns.scm
1415    arguments                       1415    arguments
1416    native-inputs                   1416    native-inputs
1417    propagated-inputs                   1417        propagated-inputs
1418    sunxi-tools-source                  1418        sunxi-tools-source
1419    file-name                           1419        file-name
1420    build-system                    1420    build-system
1421    supported-systems                   1421        supported-systems


While building in serial rather than parallel is a significant slowdown,
it seems like being able to build reproducibly might be worth the cost,
at least for certain guix variants, such as the package used for
guix-daemon... I'll likely disable parallel building for the next guix
upload to Debian, at least. :)


live well,
  vagrant

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