christoph/experimental-evaluation-of-webassembly-under-transient-fault-conditions-for-safety-critical-systems
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Small improvements after feedback (citing, footnotes, methodology)

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christoph
2026-07-07 16:04:59 +02:00
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chapters/03_background/03_01_wasm.tex
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The open \Acrfull{wasm} standard defines a portable virtual instruction set architecture, binary code format and text format for execution inside a virtual (stack) machine~\autocite{wasm3spec}.
\Gls{wasm} instructions operate on an operand stack instead of registers: values are pushed and consumed through stack operations, similar to Java's virtual machine.
It is developed and maintained by the World Wide Web Consortium (W3C)\footnote{\url[2026-07-01]{https://w3.org/}} to support high-performance applications in web-based environments.
It is developed and maintained by the World Wide Web Consortium (W3C)\iffalse{}\footnote{\url[2026-07-01]{https://w3.org/}}\fi to support high-performance applications in web-based environments.
While the initial implementations of \Gls{wasm} runtime environments were confined to web browsers\footnote{In 2016, experimental \Gls{wasm} runtimes were implemented in Firefox, Google Chrome and Microsoft Edge: \url[2026-07-01]{https://hacks.mozilla.org/2016/03/a-webassembly-milestone/}}, \Gls{wasm} does not make any web-specific assumptions, so many different standalone runtimes like \textquote{Wasmtime}\footnote{\url[2026-07-01]{https://github.com/bytecodealliance/wasmtime/}} or the \Acrfull{wamr} (see \autoref{sec:wamr}) have emerged since.
Besides instructions or execution behavior, two file formats are defined by the \Gls{wasm} standard: the \Gls{wasm} \textquote{Binary Format} \iffalse{}(see \autoref{lst:wasmexample})\fi for space-efficient representation and fast transmission, and the Lisp-like \Gls{wasm} \textquote{Text Format} for human readability (see \autoref{lst:watexample}).
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During runtime, \Gls{wasm} provides memory safety, control flow integrity and independent execution (sandboxing)\footnote{\url[2026-07-01]{https://webassembly.org/docs/security/}}.
Memory safety is achieved through a bounds-checked linear memory with an inaccessible call stack\footnote{The call stack is not part of \Gls{wasm}'s linear memory but the execution environment: \url[2026-07-01]{https://bytecodealliance.github.io/wamr.dev/blog/the-wamr-memory-model/}}, preventing arbitrary memory accesses and buffer overflows.
The linear memory is a contiguous and growable byte array that is shared between the module and host.
Control flow integrity stems from structured control flow: branches target verifiable positions and function calls are index-based and verified against the function table\footnote{\url[2026-07-01]{https://clang.llvm.org/docs/ControlFlowIntegrity.html}}.
Control flow integrity stems from structured control flow: branches target verifiable positions and function calls are index-based and verified against the function table\iffalse{}\footnote{\url[2026-07-01]{https://clang.llvm.org/docs/ControlFlowIntegrity.html}}\fi.
Additionally, the running program cannot observe its (immutable) source code to prevent control flow hijacking.
Sandboxing is enforced by isolating each module's state: a module can only interact with the outside world through explicitly imported functions and resources provided by its host runtime.