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\section{Execution Environment}\label{sec:executionenvironment}

To keep the experiment setup as simple as possible, experiments are executed in a bare-metal environment without any operating system.
This has the advantage of avoiding some sources of possible non-determinism (caused, e.g., by scheduling or interrupts) during fault injection.
It also prevents any operating system code from being targeted by the \Gls{fi} framework.
While a suitable and correctly configured statically linked real-time operating system inside a controlled, emulated environment is not prone to those issues, running experiments bare-metal excludes this category of possible problems entirely.

Instead, experiments are cross-compiled to freestanding executables using \code{i386-elf-gcc} with Newlib\footnote{\url[2026-08-12]{https://sourceware.org/newlib/}} libc.
To make Newlib work inside a bare-metal environment, certain system calls must be provided by the platform, although not all of them need to be functional\footnote{\url[2026-08-12]{https://sourceware.org/newlib/libgloss.html\#Libraries-1}}:
\begin{itemize}
  \item \code{sbrk()} is required for Newlib's \code{malloc()}, \code{calloc()} and \code{realloc()} memory-management functions. Although \Gls{wamr} uses its own memory allocator implementation (see \autoref{sssec:wamrmemoryallocation}), \Gls{wasm} targets may still require a functional \code{sbrk()} if \Gls{wamr}'s \code{snprintf}/\code{vsnprintf} are used, depending on the format string.
  \item \code{read()}, \code{write()}, \code{close()}, \code{fstat()} and \code{isatty()} stubs are required for \Gls{wamr} targets. Since no filesystem or console exists in the execution environment, the stubs do not need to implement functional behavior.
  \item \code{lseek()} is required for C and \Gls{wamr} targets. A stub suffices for the same reason as above.
  \item \code{\_exit()}, \code{kill()} and \code{getpid()} are required for \Gls{wamr} targets. Implementations can be omitted, as the execution environment does not use processes.
\end{itemize}

For experiment execution, the executables are packed into Multiboot\footnote{\url[2026-07-13]{https://www.gnu.org/software/grub/manual/multiboot/multiboot.html}}-compatible disk images with GNU GRUB\footnote{\url[2026-08-12]{https://www.gnu.org/software/grub/}} embedded via \code{grub-mkrescue} and executed in \Gls{bochs} via \Gls{fail}.

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