1 files changed, 232 insertions, 0 deletions
diff --git a/bridge/bridge.zig b/bridge/bridge.zig
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+++ b/bridge/bridge.zig
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+// so the thing is right, revo isn't really that low level and we need to have a
+// thin bridge to translate shit over. Its just to setup the VM, serial ports,
+// heap shit like that.
+
+const std = @import("std");
+const revo = @import("revo");
+
+// all the VM's output goes here, boot injects this at runtime so the
+// bridge doesn't need to pull a serial port from its ass
+pub const Sink = *const fn ([]const u8) void;
+fn noopSink(_: []const u8) void {}
+var sink: Sink = noopSink;
+
+// fan a multi-slice write payload out to the sink. mirrors the shape of std.Io's
+// file_write_streaming request: an optional header, then `data`, whose LAST slice
+// is repeated `splat` times. returns the total byte count written.
+fn writeToSink(
+    header: []const u8,
+    data: []const []const u8,
+    splat: usize,
+) std.Io.Operation.FileWriteStreaming.Result {
+    if (header.len > 0) sink(header);
+    for (data[0 .. data.len -| 1]) |slice| {
+        if (slice.len > 0) sink(slice);
+    }
+    const last = data[data.len -| 1];
+    var i: usize = 0;
+    while (i < splat) : (i += 1) {
+        if (last.len > 0) sink(last);
+    }
+
+    var total: usize = header.len;
+    for (data[0 .. data.len -| 1]) |slice| total += slice.len;
+    total += last.len * splat;
+    return total;
+}
+
+// every file write (stdout, stderr, whatever) routes to the serial port; we
+// don't have a filesystem or multiple sinks yet, so there's nowhere else to go.
+fn ioOperate(_: ?*anyopaque, operation: std.Io.Operation) std.Io.Cancelable!std.Io.Operation.Result {
+    return switch (operation) {
+        .file_write_streaming => |req| .{
+            .file_write_streaming = writeToSink(req.header, req.data, req.splat),
+        },
+        .file_read_streaming => .{ .file_read_streaming = error.InputOutput },
+        .device_io_control => .{ .device_io_control = -1 },
+        .net_receive => .{ .net_receive = .{ error.NetworkDown, 0 } },
+    };
+}
+
+// no timer wired up yet, so time stands still. fine until we have the PIT/TSC.
+fn ioNow(_: ?*anyopaque, _: std.Io.Clock) std.Io.Timestamp {
+    return .{ .nanoseconds = 0 };
+}
+
+fn ioClockResolution(_: ?*anyopaque, _: std.Io.Clock) std.Io.Clock.ResolutionError!std.Io.Duration {
+    return .{ .nanoseconds = 1_000_000 };
+}
+
+// the scheduler parks fibers itself, it never needs us to actually block.
+fn ioSleep(_: ?*anyopaque, _: std.Io.Timeout) std.Io.Cancelable!void {}
+
+fn ioCrashHandler(_: ?*anyopaque) void {}
+
+// eval captures its own errors into a buffer, so this is never reached; return
+// Canceled rather than recursing into a stderr lock we can't provide.
+fn ioLockStderr(_: ?*anyopaque, _: ?std.Io.Terminal.Mode) std.Io.Cancelable!std.Io.LockedStderr {
+    return error.Canceled;
+}
+
+fn ioUnlockStderr(_: ?*anyopaque) void {}
+
+// start from std's all-failing vtable and override only what the VM touches.
+const io_vtable: std.Io.VTable = blk: {
+    var v = std.Io.failing.vtable.*;
+    v.operate = ioOperate;
+    v.now = ioNow;
+    v.clockResolution = ioClockResolution;
+    v.sleep = ioSleep;
+    v.crashHandler = ioCrashHandler;
+    v.lockStderr = ioLockStderr;
+    v.unlockStderr = ioUnlockStderr;
+    break :blk v;
+};
+
+const serial_io: std.Io = .{ .userdata = null, .vtable = &io_vtable };
+
+// A second IO used only as std's debug IO (for std.debug.print, which revo hits
+// on a few error paths). std's default debug IO is a threaded stderr writer that
+// doesn't exist on freestanding, and std.Io.failing's stderr path is literally
+// `unreachable` -- so we give std a real one that drains to the same sink. Unlike
+// serial_io above, its lockStderr must return an actual File.Writer (std turns a
+// Canceled lock into a panic), and swapCancelProtection must not be unreachable.
+var dbg_fw: std.Io.File.Writer = undefined;
+var dbg_fw_buf: [256]u8 = undefined;
+
+fn dbgLockStderr(_: ?*anyopaque, _: ?std.Io.Terminal.Mode) std.Io.Cancelable!std.Io.LockedStderr {
+    // File.stderr() reads posix.STDERR_FILENO, which doesn't exist on
+    // freestanding. Build the File by hand instead; ioOperate ignores the handle
+    // and routes every write to the sink regardless.
+    const stderr_file: std.Io.File = .{ .handle = undefined, .flags = .{ .nonblocking = false } };
+    dbg_fw = stderr_file.writerStreaming(debug_io, &dbg_fw_buf);
+    return .{ .file_writer = &dbg_fw, .terminal_mode = .no_color };
+}
+fn dbgUnlockStderr(_: ?*anyopaque) void {
+    dbg_fw.interface.flush() catch {};
+}
+fn dbgSwapCancel(_: ?*anyopaque, new: std.Io.CancelProtection) std.Io.CancelProtection {
+    return new;
+}
+
+const debug_io_vtable: std.Io.VTable = blk: {
+    var v = std.Io.failing.vtable.*;
+    v.operate = ioOperate;
+    v.now = ioNow;
+    v.clockResolution = ioClockResolution;
+    v.sleep = ioSleep;
+    v.crashHandler = ioCrashHandler;
+    v.lockStderr = dbgLockStderr;
+    v.unlockStderr = dbgUnlockStderr;
+    v.swapCancelProtection = dbgSwapCancel;
+    break :blk v;
+};
+
+pub const debug_io: std.Io = .{ .userdata = null, .vtable = &debug_io_vtable };
+
+// an unbuffered std.Io.Writer that drains straight to the sink, so we can render
+// revo's own error reports (which write to a std.Io.Writer) onto the console.
+const SinkWriter = struct {
+    interface: std.Io.Writer,
+
+    fn init() SinkWriter {
+        return .{ .interface = .{ .buffer = &.{}, .vtable = &.{ .drain = drain, .flush = flush }, .end = 0 } };
+    }
+
+    fn drain(w: *std.Io.Writer, data: []const []const u8, splat: usize) std.Io.Writer.Error!usize {
+        _ = w;
+        var total: usize = 0;
+        for (data[0 .. data.len -| 1]) |s| {
+            if (s.len > 0) sink(s);
+            total += s.len;
+        }
+        const last = data[data.len -| 1];
+        var i: usize = 0;
+        while (i < splat) : (i += 1) {
+            if (last.len > 0) sink(last);
+        }
+        total += last.len * splat;
+        return total;
+    }
+
+    fn flush(_: *std.Io.Writer) std.Io.Writer.Error!void {}
+};
+
+// bring up the VM on the kernel heap and run a revo program. this is the "hello
+// world" that proves the whole stack: revo compiled for bare metal, our
+// allocator feeding it, its stdout coming out our serial port.
+pub fn run(alloc: std.mem.Allocator, out: Sink) void {
+    sink = out;
+
+    // NOTE: we drive the VM directly (compile -> run) instead of the high-level
+    // Runtime.eval wrapper. that wrapper has a latent type error in revo (it
+    // names module.EvalResult, which doesn't exist) that only trips when it's
+    // actually analyzed -- we're the first caller. this is the same low-level
+    // path revo's own wasm entry uses, so it's the well-trodden one anyway.
+    const VM = revo.VM;
+    const vm = alloc.create(VM) catch {
+        out("bridge: OOM creating VM\r\n");
+        return;
+    };
+    defer alloc.destroy(vm);
+    vm.* = VM.init(.{
+        .alloc = alloc,
+        .io = serial_io,
+        .argv = &.{},
+        .diag_alloc = alloc,
+    }) catch {
+        out("bridge: VM.init failed\r\n");
+        return;
+    };
+    defer vm.deinit();
+    out("bridge: revo VM up\r\n");
+
+    // a proper workout, not just a print: recursion (call frames + soft-float
+    // arithmetic), string methods (real stdlib), tables, tuples, destructuring.
+    const src =
+        \\fn fib(n) do
+        \\  if n < 2 n
+        \\  else fib(n - 1) + fib(n - 2)
+        \\end
+        \\print("hello from revo")
+        \\print("fib(10) =", fib(10))
+        \\print("arith  =", 1 + 2 * 3, 10 / 4)
+        \\print("string =", "revo":upper(), "KERNEL":lower())
+        \\const arr = {10, 20, 30}
+        \\print("table  =", arr, arr[0])
+        \\const (a, b) = (3, 4)
+        \\print("tuple  =", a + b)
+    ;
+    const build_result = revo.lang.build(vm, .{ .name = "kernel", .text = src }, .{}) catch {
+        out("bridge: compile threw\r\n");
+        return;
+    };
+    const artifact = switch (build_result) {
+        .ok => |art| art,
+        .err => {
+            out("bridge: compile error\r\n");
+            return;
+        },
+    };
+    defer alloc.free(artifact.instructions);
+    defer alloc.free(artifact.spans);
+
+    vm.setProgramDebugInfo(artifact.spans, "", "kernel") catch {
+        out("bridge: setProgramDebugInfo failed\r\n");
+        return;
+    };
+
+    const eval_result = revo.module.runCompiledModuleReport(vm, "kernel", artifact.instructions) catch {
+        out("bridge: eval threw\r\n");
+        return;
+    };
+    switch (eval_result) {
+        .ok => out("\r\nbridge: eval ok\r\n"),
+        .err => |failure| {
+            out("\r\nbridge: runtime error: ");
+            var sw = SinkWriter.init();
+            failure.render(alloc, &sw.interface, src) catch {};
+            out("\r\n");
+        },
+    }
+}