feat: add gdb support to zba

.gitmodules

@@ -13,3 +13,6 @@
 [submodule "lib/zig-toml"]
 	path = lib/zig-toml
 	url = https://github.com/aeronavery/zig-toml
+[submodule "lib/zba-gdbstub"]
+	path = lib/zba-gdbstub
+	url = https://git.musuka.dev/paoda/zba-gdbstub

build.zig

@@ -1,6 +1,8 @@
 const std = @import("std");
 const builtin = @import("builtin");
+
 const Sdk = @import("lib/SDL.zig/Sdk.zig");
+const Gdbstub = @import("lib/zba-gdbstub/build.zig");
 
 pub fn build(b: *std.build.Builder) void {
     // Minimum Zig Version
@@ -43,6 +45,9 @@ pub fn build(b: *std.build.Builder) void {
     // OpenGL 3.3 Bindings
     exe.addPackagePath("gl", "lib/gl.zig");
 
+    // gdbstub
+    Gdbstub.link(exe);
+
     // Zig SDL Bindings: https://github.com/MasterQ32/SDL.zig
     const sdk = Sdk.init(b);
     sdk.link(exe, .dynamic);

lib/SDL.zig

@@ -1 +1 @@
-Subproject commit 2fbd4b228516bf08348a3173f1446c7e8d75540a
+Subproject commit 2025889b612f345698feff44fc245501bff637e9

lib/known-folders

@@ -1 +1 @@
-Subproject commit 24845b0103e611c108d6bc334231c464e699742c
+Subproject commit 6b37490ac7285133bf09441850b8102c9728a776

lib/zba-gdbstub

@@ -0,0 +1 @@
+Subproject commit 4bca44e5f2a4aa19361b51b7617a21f46f88eef4

lib/zig-clap

@@ -1 +1 @@
-Subproject commit 88edafd00ec25dcc01deb8fc69e9864a16f8717c
+Subproject commit 6c9ca9025199b145c42a75d10cadb3f97879ee6d

src/core/emu.zig

@@ -163,3 +163,59 @@ fn sleep(timer: *Timer, wake_time: u64) ?u64 {
 fn spinLoop(timer: *Timer, wake_time: u64) void {
     while (true) if (timer.read() > wake_time) break;
 }
+
+pub const EmuThing = struct {
+    const Self = @This();
+    const Interface = @import("gdbstub").Emulator;
+
+    cpu: *Arm7tdmi,
+    scheduler: *Scheduler,
+
+    pub fn init(cpu: *Arm7tdmi, scheduler: *Scheduler) Self {
+        return .{ .cpu = cpu, .scheduler = scheduler };
+    }
+
+    pub fn interface(self: *Self) Interface {
+        return Interface.init(self);
+    }
+
+    pub fn read(self: *const Self, addr: u32) u8 {
+        return self.cpu.bus.dbgRead(u8, addr);
+    }
+
+    pub fn write(self: *Self, addr: u32, value: u8) void {
+        _ = value;
+        _ = self;
+        _ = addr;
+
+        std.debug.panic("TODO: Implement Debug Writes?", .{});
+    }
+
+    pub fn registers(self: *const Self) *[16]u32 {
+        return &self.cpu.r;
+    }
+
+    pub fn cpsr(self: *const Self) u32 {
+        return self.cpu.cpsr.raw;
+    }
+
+    pub fn step(self: *Self) void {
+        const cpu = self.cpu;
+        const sched = self.scheduler;
+
+        // TODO: How can I make it easier to keep this in lock-step with runFrame?
+        while (true) {
+            if (!cpu.stepDmaTransfer()) {
+                if (cpu.isHalted()) {
+                    // Fast-forward to next Event
+                    sched.tick = sched.queue.peek().?.tick;
+                } else {
+                    cpu.step();
+                    break; // this function won't return until we've actually stepped once
+                }
+            }
+
+            if (sched.tick >= sched.nextTimestamp()) sched.handleEvent(cpu);
+        }
+    }
+};

src/core/ppu.zig

@@ -843,7 +843,12 @@ pub const Ppu = struct {
                 const is_top_layer = (top_layer >> layer) & 1 == 1;
 
                 if (is_top_layer) {
+                    const pixel = self.scanline.btm()[i];
+
+                    // FIXME: Can't I do this check ealier? Test Amazing Mirror File Select, bld_demo.gba
+                    if (!pixel.isSet())
                         self.scanline.btm()[i] = Scanline.Pixel.from(.Background, bgr555); // this is intentional
+
                     return;
                 }
             },

src/main.zig

@@ -22,6 +22,7 @@ const params = clap.parseParamsComptime(
     \\-h, --help            Display this help and exit.
     \\-s, --skip            Skip BIOS.
     \\-b, --bios <str>      Optional path to a GBA BIOS ROM.
+    \\ --gdb                Run ZBA from the context of a GDB Server
     \\<str>                 Path to the GBA GamePak ROM.
     \\
 );
@@ -87,11 +88,38 @@ pub fn main() void {
         cpu.fastBoot();
     }
 
+    if (result.args.gdb) {
+        const Server = @import("gdbstub").Server;
+        const EmuThing = @import("core/emu.zig").EmuThing;
+
+        var emu_thing = EmuThing.init(&cpu, &scheduler);
+        const emulator = emu_thing.interface();
+
+        {
+            const frames_per_second: usize = 60;
+            const emu = @import("core/emu.zig");
+
+            var i: usize = 0;
+            while (i < frames_per_second * 120) : (i += 1) {
+                emu.runFrame(&scheduler, &cpu);
+
+                std.debug.print("Frame {:0>3}/{:0>3}\r", .{ i, frames_per_second * 120 });
+            }
+        }
+
+        log.info("Ready to connect", .{});
+
+        var server = Server.init(emulator) catch |e| exitln("failed to init gdb server: {}", .{e});
+        defer server.deinit(allocator);
+
+        server.run(allocator) catch |e| exitln("gdb server crashed: {}", .{e});
+    } else {
         var gui = Gui.init(&bus.pak.title, &bus.apu, width, height) catch |e| exitln("failed to init gui: {}", .{e});
         defer gui.deinit();
 
         gui.run(&cpu, &scheduler) catch |e| exitln("failed to run gui thread: {}", .{e});
     }
+}
 
 pub fn handleArguments(allocator: Allocator, data_path: []const u8, result: *const clap.Result(clap.Help, &params, clap.parsers.default)) !FilePaths {
     const rom_path = romPath(result);