Foundations
What a system call really is, and the two disciplines this book never stops practicing — how each language reports failure, and how each language shares work.
Syscalls and the ABI
What a system call really is — the syscall instruction, the register-level kernel ABI, and the vDSO fast path — traced through sysprobe, one specimen program that shows how glibc, the Go runtime, and rustix each reach the same kernel.
Errors, three ways
One error's journey from a failing write(2) into std::expected, a wrapped Go error, and a Rust Result — copyx establishes the book's error taxonomy, the strerror(3) message contract, and the EINTR retry policy every later chapter reuses.
Concurrency, three ways
The second thread that runs the whole book — how each language shares work over the same kernel threads. C++23 jthreads and stop tokens, Go's runtime and channels, Rust's compiler-refereed sharing — one parallel checksummer, byte-identical output, and a SIGINT drain you can watch happen.