add support for a zisk guest program

[gballet]

No description provided.

[Copilot]

Pull Request Overview

This PR adds support for a Zisk guest program by providing a RISC-V64 linker script, startup assembly, Zig runtime modules (lib, io, layout), and registering a new zisk target in the build system.

• Defined memory regions and sections in zisk.ld for ROM/RAM layout
• Implemented _start assembly stub to set up gp and sp, then call main
• Added Zig modules for I/O (get_input, print_str), layout constants, and a halt runtime
• Registered the zisk target in build.zig

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pkgs/state-transition-runtime/src/zisk/zisk.ld	Linker script for ROM/RAM memory regions and section layout
pkgs/state-transition-runtime/src/zisk/start.s	Assembly entrypoint initializing registers and tail-calling main
pkgs/state-transition-runtime/src/zisk/lib.zig	Runtime functions: halt and free_input
pkgs/state-transition-runtime/src/zisk/layout.zig	Memory-mapped I/O address constants
pkgs/state-transition-runtime/src/zisk/io.zig	get_input and print_str implementations for Zisk
build.zig	Adds the zisk target configuration to the build script

Comments suppressed due to low confidence (1)

pkgs/state-transition-runtime/src/zisk/io.zig:6

• These new I/O functions (get_input, print_str) don’t have tests yet; consider adding unit or integration tests to verify input-size parsing and UART write behavior.

pub fn get_input(_: std.mem.Allocator) []const u8 {

[Copilot]

The halt function ignores its code parameter and uses a hardcoded exit code. Consider passing the code argument into the ecall (in a0) or the QEMU exit store instead of always using 0x5555.

Suggested change

	pub fn halt(_: u32) noreturn {
	const arch_id_zisk = asm volatile ("csrr %[ret], marchid"
	: [ret] "=r" (-> usize),
	);
	if (arch_id_zisk == 0xFFFEEE) {
	// Zisk exit
	asm volatile (
	\\ li a7, 93
	\\ ecall
	);
	} else {
	// QEMU exit
	//"li t0, {_QEMU_EXIT_ADDR}",
	//"li t1, {_QEMU_EXIT_CODE}",
	asm volatile (
	\\ li t0, 0x100000
	\\ li t1, 0x5555
	pub fn halt(code: u32) noreturn {
	const arch_id_zisk = asm volatile ("csrr %[ret], marchid"
	: [ret] "=r" (-> usize),
	);
	if (arch_id_zisk == 0xFFFEEE) {
	// Zisk exit
	asm volatile (
	\\ mv a0, {code}
	\\ li a7, 93
	\\ ecall
	);
	} else {
	// QEMU exit
	asm volatile (
	\\ li t0, 0x100000
	\\ mv t1, {code}

[Copilot]

[nitpick] Extract the hardcoded exit-store address 0x100000 and exit code 0x5555 into named constants to clarify their intention in the QEMU path.

Suggested change

	\\ li t0, 0x100000
	\\ li t1, 0x5555
	\\ li t0, QEMU_EXIT_ADDR
	\\ li t1, QEMU_EXIT_CODE