Cross-Compile ARM with QEMU

Build arm64 on x86, Run With QEMU

Cross-compilation targets a different ISA than the host CPU. Docker buildx and GitHub Actions arm64 runners use the same toolchain flow: aarch64-linux-gnu-gcc emits arm64 ELF, qemu-aarch64 translates instructions and forwards syscalls to the host kernel.

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• as/ld prefixed with the triplet produce arm64 objects on an x86 laptop
• qemu-aarch64 user-mode is not full system emulation; it maps Linux arm64 binaries
• Static qemu-aarch64-static inside containers powers multi-arch pulls

Failures often show up as wrong syscall numbers or linker scripts meant for x86.

For this exercise, you will cross-assemble a small program and run it under QEMU. This task asks you to verify output matches native expectations, because Raspberry Pi OS images and arm64 containers on Docker Hub are built exactly this way when CI lacks bare metal.

Keep the relevant man page, ABI doc, or Rust reference chapter open while you work. When your output disagrees with the reference implementation on the same machine, the mismatch is usually an alignment rule, an off-by-one terminator, or a register slot you misread in GDB. Skim the official documentation for the tool or ABI named in the exercise; the prose changes, but register roles, syscall numbers, and ownership rules stay stable across releases.