251 lines
6.4 KiB
TeX
251 lines
6.4 KiB
TeX
\documentclass[12pt]{beamer}
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\usetheme{metropolis}
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\newenvironment{code}{\ttfamily}{\par}
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\title{Where does \textit{your} compiler come from?}
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\date{2018-03-13}
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\author{Vincent Ambo}
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\institute{Norwegian Unix User Group}
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\begin{document}
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\maketitle
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%% Slide 1:
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\section{Introduction}
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%% Slide 2:
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\begin{frame}{Chicken and egg}
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Self-hosted compilers are often built using themselves, for example:
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\begin{itemize}
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\item C-family compilers bootstrap themselves \& each other
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\item (Some!) Common Lisp compilers can bootstrap each other
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\item \texttt{rustc} bootstraps itself with a previous version
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\item ... same for many other languages!
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\end{itemize}
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\end{frame}
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\begin{frame}{Chicken, egg and ... lizard?}
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It's not just compilers: Languages have runtimes, too.
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\begin{itemize}
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\item JVM is implemented in C++
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\item Erlang-VM is C
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\item Haskell runtime is C
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\end{itemize}
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... we can't ever get away from C, can we?
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\end{frame}
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%% Slide 3:
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\begin{frame}{Trusting Trust}
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\begin{center}
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\huge{Could this be exploited?}
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\end{center}
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\end{frame}
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%% Slide 4:
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\begin{frame}{Short interlude: A quine}
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\begin{center}
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\begin{code}
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((lambda (x) (list x (list 'quote x)))
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\newline\vspace*{6mm} '(lambda (x) (list x (list 'quote x))))
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\end{code}
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\end{center}
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\end{frame}
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%% Slide 5:
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\begin{frame}{Short interlude: Quine Relay}
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\begin{center}
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\includegraphics[
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keepaspectratio=true,
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height=\textheight
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]{quine-relay.png}
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\end{center}
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\end{frame}
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%% Slide 6:
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\begin{frame}{Trusting Trust}
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An attack described by Ken Thompson in 1983:
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\begin{enumerate}
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\item Modify a compiler to detect when it's compiling itself.
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\item Let the modification insert \textit{itself} into the new compiler.
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\item Add arbitrary attack code to the modification.
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\item \textit{Optional!} Remove the attack from the source after compilation.
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\end{enumerate}
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\end{frame}
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%% Slide 7:
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\begin{frame}{Damage potential?}
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\begin{center}
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\large{Let your imagination run wild!}
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\end{center}
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\end{frame}
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%% Slide 8:
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\section{Countermeasures}
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%% Slide 9:
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\begin{frame}{Diverse Double-Compiling}
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Assume we have:
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\begin{itemize}
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\item Target language compilers $A$ and $T$
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\item The source code of $A$: $ S_{A} $
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\end{itemize}
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\end{frame}
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%% Slide 10:
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\begin{frame}{Diverse Double-Compiling}
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Apply the first stage (functional equivalence):
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\begin{itemize}
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\item $ X = A(S_{A})$
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\item $ Y = T(S_{A})$
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\end{itemize}
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Apply the second stage (bit-for-bit equivalence):
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\begin{itemize}
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\item $ V = X(S_{A})$
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\item $ W = Y(S_{A})$
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\end{itemize}
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Now we have a new problem: Reproducibility!
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\end{frame}
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%% Slide 11:
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\begin{frame}{Reproducibility}
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Bit-for-bit equivalent output is hard, for example:
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\begin{itemize}
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\item Timestamps in output artifacts
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\item Non-deterministic linking order in concurrent builds
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\item Non-deterministic VM \& memory states in outputs
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\item Randomness in builds (sic!)
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\end{itemize}
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\end{frame}
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\begin{frame}{Reproducibility}
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\begin{center}
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Without reproducibility, we can never trust that any shipped
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binary matches the source code!
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\end{center}
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\end{frame}
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%% Slide 12:
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\section{(Partial) State of the Union}
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\begin{frame}{The Desired State}
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\begin{center}
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\begin{enumerate}
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\item Full-source bootstrap!
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\item All packages reproducible!
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\end{enumerate}
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\end{center}
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\end{frame}
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%% Slide 13:
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\begin{frame}{Bootstrapping Debian}
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\begin{itemize}
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\item Sparse information on the Debian-wiki
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\item Bootstrapping discussions mostly resolve around new architectures
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\item GCC is compiled by depending on previous versions of GCC
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\end{itemize}
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\end{frame}
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\begin{frame}{Reproducing Debian}
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Debian has a very active effort for reproducible builds:
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\begin{itemize}
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\item Organised information about reproducibility status
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\item Over 90\% reproducibility in Debian package base!
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\end{itemize}
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\end{frame}
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\begin{frame}{Short interlude: Nix}
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\begin{center}
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\includegraphics[
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keepaspectratio=true,
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height=0.7\textheight
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]{nixos-logo.png}
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\end{center}
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\end{frame}
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\begin{frame}{Short interlude: Nix}
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\begin{center}
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\includegraphics[
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keepaspectratio=true,
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height=0.90\textheight
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]{drake-meme.png}
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\end{center}
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\end{frame}
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\begin{frame}{Short interlude: Nix}
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\begin{center}
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\includegraphics[
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keepaspectratio=true,
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height=0.7\textheight
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]{nixos-logo.png}
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\end{center}
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\end{frame}
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\begin{frame}{Bootstrapping NixOS}
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Nix evaluation can not recurse forever: The bootstrap can not
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simply depend on a previous GCC.
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Workaround: \texttt{bootstrap-tools} tarball from a previous
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binary cache is fetched and used.
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An unfortunate magic binary blob ...
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\end{frame}
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\begin{frame}{Reproducing NixOS}
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Not all reproducibility patches have been ported from Debian.
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However: Builds are fully repeatable via the Nix fundamentals!
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\end{frame}
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\section{Future Developments}
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\begin{frame}{Bootstrappable: stage0}
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Hand-rolled ``Cthulhu's Path to Madness'' hex-programs:
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\begin{itemize}
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\item No non-auditable binary blobs
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\item Aims for understandability by 70\% of programmers
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\item End goal is a full-source bootstrap of GCC
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\end{itemize}
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\end{frame}
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\begin{frame}{Bootstrappable: MES}
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Bootstrapping the ``Maxwell Equations of Software'':
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\begin{itemize}
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\item Minimal C-compiler written in Scheme
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\item Minimal Scheme-interpreter (currently in C, but intended to
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be rewritten in stage0 macros)
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\item End goal is full-source bootstrap of the entire GuixSD
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\end{itemize}
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\end{frame}
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\begin{frame}{Other platforms}
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\begin{itemize}
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\item Nix for Darwin is actively maintained
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\item F-Droid Android repository works towards fully reproducible
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builds of (open) Android software
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\item Mobile devices (phones, tablets, etc.) are a lost cause at
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the moment
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\end{itemize}
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\end{frame}
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\begin{frame}{Thanks!}
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Resources:
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\begin{itemize}
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\item bootstrappable.org
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\item reproducible-builds.org
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\end{itemize}
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@tazjin | mail@tazj.in
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\end{frame}
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\end{document}
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