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Apps now run in ring 3 (see crt0.c), so a plain near call to the kernel's fixed function-pointer table can't be trusted: paging lets ring 3 execute those addresses, but a privileged instruction inside one (e.g. b_system's IRQ_ENABLE/IRQ_DISABLE) still runs at CPL 3 and #GPs, since a near call doesn't change CS/CPL. Every b_* call now traps via int $0x80 with R9 = the syscall index instead, so the kernel's own int_syscall gate can issue the call from ring 0. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Adds a custom rustc target (port/rust_port/x86_64-baremetal-firecracker.json) reusing std's Linux-musl backend, since this port's musl is stock musl 1.2.6 with only its syscall trap redirected (see musl_port/musl-1.2.6-baremetal.patch) -- ABI-compatible enough that no patch to Rust's own std source was needed, just link-time stubs for the backtrace unwinder this port has no runtime for (port/rust_port/unwind_stub.c). build-rust-app.sh mirrors build-app.sh's own two-stage compile-then-link shape. scripts/get-rust.sh pins and installs the nightly toolchain -Z build-std needs. Verified end to end under Firecracker: a println! app boots and prints, and std::fs::write/read_to_string/remove_file work against disk.img's ext2 filesystem. std::thread is not yet supported -- see RUST.md for the full writeup, what's verified, and known gaps. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Summary
libBareMetal.csyscall throughint $0x80(with R9 = syscall index) instead of a plain near call, since apps now run in ring 3 and a near call into a privileged instruction (e.g.b_system's IRQ_ENABLE/IRQ_DISABLE) would #GP without a real CPL change.std(not justno_std): a custom rustc target reusingstd's Linux-musl backend (this port's musl is stock musl 1.2.6 with only its syscall trap redirected, so it's ABI-compatible enough that no patch to Rust's own std source was needed -- just link-time stubs for the backtrace unwinder this port has no runtime for). SeeRUST.mdfor the full writeup.Test plan
println!app builds withbuild-rust-app.shand boots, printing to the console.std::fs::write/read_to_string/remove_filework againstdisk.img's ext2 filesystem.std::threadis known-broken (panics during thread teardown) -- documented as unsupported inRUST.md, not yet fixed.std::netis architecturally expected to work but has not been smoke-tested end to end.🤖 Generated with Claude Code