feat: add VM snapshot support for fast restore boot

[ppenna]

Summary

Trigger a Nanvix VM snapshot after Py_Initialize() completes. On first boot the hypervisor creates a snapshot; subsequent boots restore from it in ~35 ms instead of cold-booting (~825 ms).

Changes

• Modules/nanvix_snapshot.S: New file — standalone assembly syscall helper (int $0x80, syscall 35) in a separate .S file to survive LTO elimination
• Modules/main.c: Call nanvix_snapshot() after initialization, gated by #ifdef __nanvix__
• Makefile.nanvix: Compile and link nanvix_snapshot.o in both Docker and non-Docker build paths, with post-injection validation to fail loudly if the Makefile injection doesn't match

Companion

Requires nanvix/nanvix snapshot restore CLI flag.

Split from #314.

[Copilot]

Pull request overview

Adds Nanvix VM snapshot triggering to enable fast “restore boot” by snapshotting the VM immediately after CPython initialization completes.

Changes:

• Introduces a Nanvix snapshot syscall helper implemented as a standalone assembly routine.
• Calls the snapshot trigger right after Py_InitializeFromConfig() succeeds (Nanvix-only).
• Updates Nanvix cross-build Makefile to compile/link the snapshot helper in both Docker and non-Docker build flows (via Makefile injection).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
Modules/nanvix_snapshot.S	New assembly helper exporting nanvix_snapshot() using int $0x80 syscall 35.
Modules/main.c	Adds nanvix_snapshot() declaration and calls it after initialization under #ifdef __nanvix__.
Makefile.nanvix	Compiles nanvix_snapshot.S and injects nanvix_snapshot.o into the generated build Makefile for linking.

Comments suppressed due to low confidence (1)

Makefile.nanvix:223

• Same issue in the non-Docker path: the sed substitution appends text after a line that likely ends with a trailing \ continuation in MODULE_OBJS, which will break the generated Makefile. Modify the injection to add Modules/nanvix_snapshot.o as its own continued line (or insert before the trailing \) specifically inside the MODULE_OBJS= assignment.

	@# Inject the snapshot object into the generated Makefile's MODULE_OBJS
	@grep -q "nanvix_snapshot.o" Makefile || \
		{ sed -i "/Modules\/main\.o/s|$$| Modules/nanvix_snapshot.o|" Makefile && \
		  grep -q "nanvix_snapshot.o" Makefile || \
		  { echo "Error: failed to inject nanvix_snapshot.o into Makefile"; exit 1; }; }

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The sed-based Makefile injection appends Modules/nanvix_snapshot.o to the end of the line matching Modules/main.o. In the generated Makefile, that line ends with a trailing \ continuation, so appending after it will move the backslash away from end-of-line and break the MODULE_OBJS definition (likely causing a Makefile parse error). Adjust the injection to insert a new line entry (or insert before the trailing \) within the MODULE_OBJS block instead of appending after end-of-line.

This issue also appears on line 219 of the same file.