feat: Add basic gdbserver feature

Initially I began implementing the gdb protocol on my own, but I then found a
nice work-in-progress crate on https://github.com/daniel5151/gdbstub
that suited my needs.


Former-commit-id: f77557cbbd8652c2ed05ac439efc1956d8e99729

Cargo.toml

@@ -37,6 +37,8 @@ arrayvec = "0.5.1"
 
 rustyline = {version = "6.0.0", optional = true}
 nom = {version = "5.0.0", optional = true}
+gdbstub = {git = "https://github.com/daniel5151/gdbstub.git", optional = true, features = ["std"], rev = "9686df6d74c4bf45cbc5746273b82640e8852b6d"}
+
 
 [[bin]]
 name = "rba-sdl2"
@@ -51,6 +53,7 @@ path = "src/plat/minifb/main.rs"
 
 [features]
 debugger = ["nom", "rustyline"]
+gdb = ["gdbstub"]
 
 [profile.dev]
 opt-level = 0

README.md

@@ -84,6 +84,8 @@ Special key bindings
 | Key          	| Function          	|
 |--------------	|--------------------	|
 | Space (hold) 	| Disable 60fps cap  	|
+| F1		| Custom debugger (requires --features debugger) |
+| F2		| Spawn gdbserver (experimetnal, requires --features gdb) |
 | F5           	| Save snapshot file 	|
 | F9           	| Load snapshot file 	|
 

src/core/arm7tdmi/cpu.rs

@@ -8,9 +8,10 @@ use std::fmt;
 
 pub use super::exception::Exception;
 use super::CpuAction;
+#[cfg(feature = "debugger")]
+use super::DecodedInstruction;
 use super::{
-    arm::*, psr::RegPSR, thumb::ThumbInstruction, Addr, CpuMode, CpuState, DecodedInstruction,
-    InstructionDecoder,
+    arm::*, psr::RegPSR, thumb::ThumbInstruction, Addr, CpuMode, CpuState, InstructionDecoder,
 };
 
 use crate::core::bus::Bus;
@@ -34,6 +35,8 @@ pub struct Core {
     pub(super) bs_carry_out: bool,
 
     pipeline: [u32; 2],
+
+    #[cfg(feature = "debugger")]
     pub last_executed: Option<DecodedInstruction>,
 
     pub cycles: usize,
@@ -296,8 +299,8 @@ impl Core {
         #[cfg(feature = "debugger")]
         {
             self.gpr_previous = self.get_registers();
-        }
             self.last_executed = Some(DecodedInstruction::Arm(decoded_arm));
+        }
         let result = self.exec_arm(sb, decoded_arm);
         match result {
             CpuAction::AdvancePC => self.advance_arm(),
@@ -310,8 +313,8 @@ impl Core {
         #[cfg(feature = "debugger")]
         {
             self.gpr_previous = self.get_registers();
-        }
             self.last_executed = Some(DecodedInstruction::Thumb(decoded_thumb));
+        }
         let result = self.exec_thumb(sb, decoded_thumb);
         match result {
             CpuAction::AdvancePC => self.advance_thumb(),
@@ -320,7 +323,7 @@ impl Core {
     }
 
     #[inline]
-    pub(super) fn reload_pipeline16(&mut self, sb: &mut SysBus) {
+    pub fn reload_pipeline16(&mut self, sb: &mut SysBus) {
         self.pipeline[0] = sb.read_16(self.pc) as u32;
         self.N_cycle16(sb, self.pc);
         self.advance_thumb();
@@ -330,7 +333,7 @@ impl Core {
     }
 
     #[inline]
-    pub(super) fn reload_pipeline32(&mut self, sb: &mut SysBus) {
+    pub fn reload_pipeline32(&mut self, sb: &mut SysBus) {
         self.pipeline[0] = sb.read_32(self.pc);
         self.N_cycle16(sb, self.pc);
         self.advance_arm();

src/core/gba.rs

@@ -19,11 +19,11 @@ pub struct GameBoyAdvance {
     pub sysbus: Box<SysBus>,
     pub cpu: arm7tdmi::Core,
 
-    video_device: Rc<RefCell<dyn VideoInterface>>,
-    audio_device: Rc<RefCell<dyn AudioInterface>>,
-    input_device: Rc<RefCell<dyn InputInterface>>,
+    pub video_device: Rc<RefCell<dyn VideoInterface>>,
+    pub audio_device: Rc<RefCell<dyn AudioInterface>>,
+    pub input_device: Rc<RefCell<dyn InputInterface>>,
 
-    cycles_to_next_event: usize,
+    pub cycles_to_next_event: usize,
 }
 
 #[derive(Serialize, Deserialize)]
@@ -120,8 +120,8 @@ impl GameBoyAdvance {
         self.sysbus.io.gpu.skip_bios();
     }
 
-    fn step_cpu(&mut self, io: &mut IoDevices) -> usize {
-        if io.intc.irq_pending() && self.cpu.last_executed.is_some() {
+    pub fn step_cpu(&mut self, io: &mut IoDevices) -> usize {
+        if io.intc.irq_pending() {
             self.cpu.irq(&mut self.sysbus);
             io.haltcnt = HaltState::Running;
         }
@@ -131,7 +131,7 @@ impl GameBoyAdvance {
     }
 
     pub fn step(&mut self) {
-        // // I hate myself for doing this, but rust left me no choice.
+        // I hate myself for doing this, but rust left me no choice.
         let io = unsafe {
             let ptr = &mut *self.sysbus as *mut SysBus;
             &mut (*ptr).io as &mut IoDevices

src/gdb.rs

@@ -0,0 +1,142 @@
+use super::core::arm7tdmi::CpuState;
+use super::core::interrupt::*;
+use super::core::iodev::IoDevices;
+use super::core::sysbus::SysBus;
+use super::core::Bus;
+use super::core::GameBoyAdvance;
+
+use byteorder::{LittleEndian, ReadBytesExt};
+use gdbstub::{Access, GdbStub, Target, TargetState};
+
+use std::fmt;
+use std::io::Cursor;
+use std::net::{TcpListener, TcpStream, ToSocketAddrs};
+
+pub type GdbServer = GdbStub<GameBoyAdvance, TcpStream>;
+
+pub fn spawn_gdb_server<A: ToSocketAddrs + fmt::Display>(
+    addr: A,
+) -> Result<GdbServer, Box<dyn std::error::Error>> {
+    info!("spawning gdbserver, listening on {}", addr);
+
+    let sock = TcpListener::bind(addr)?;
+    let (stream, addr) = sock.accept()?;
+    info!("got connection from {}", addr);
+
+    Ok(GdbServer::new(stream))
+}
+
+impl Target for GameBoyAdvance {
+    type Usize = u32;
+    type Error = ();
+
+    fn step(
+        &mut self,
+        mut _log_mem_access: impl FnMut(Access<u32>),
+    ) -> Result<TargetState, Self::Error> {
+        static mut S_TOTAL_CYCLES: usize = 0;
+
+        let io = unsafe {
+            let ptr = &mut *self.sysbus as *mut SysBus;
+            &mut (*ptr).io as &mut IoDevices
+        };
+
+        // clear any pending DMAs
+        let mut irqs = IrqBitmask(0);
+        while io.dmac.is_active() {
+            io.dmac.perform_work(&mut self.sysbus, &mut irqs);
+        }
+        io.intc.request_irqs(irqs);
+
+        // run the CPU, ignore haltcnt
+        let cycles = self.step_cpu(io);
+        io.timers.update(cycles, &mut self.sysbus, &mut irqs);
+
+        unsafe {
+            S_TOTAL_CYCLES += cycles;
+        }
+
+        if self.cycles_to_next_event <= unsafe { S_TOTAL_CYCLES } {
+            let mut cycles_to_next_event = std::usize::MAX;
+            io.gpu.step(
+                unsafe { S_TOTAL_CYCLES },
+                &mut self.sysbus,
+                &mut irqs,
+                &mut cycles_to_next_event,
+                &self.video_device,
+            );
+            io.sound.update(
+                unsafe { S_TOTAL_CYCLES },
+                &mut cycles_to_next_event,
+                &self.audio_device,
+            );
+            self.cycles_to_next_event = cycles_to_next_event;
+
+            unsafe {
+                S_TOTAL_CYCLES = 0;
+            };
+        } else {
+            self.cycles_to_next_event -= unsafe { S_TOTAL_CYCLES };
+        }
+
+        io.intc.request_irqs(irqs);
+
+        Ok(TargetState::Running)
+    }
+
+    fn read_pc(&mut self) -> u32 {
+        self.cpu.get_next_pc()
+    }
+
+    // read the specified memory addresses from the target
+    fn read_addrs(&mut self, addr: std::ops::Range<u32>, mut push_byte: impl FnMut(u8)) {
+        for addr in addr {
+            push_byte(self.sysbus.read_8(addr))
+        }
+    }
+
+    // write data to the specified memory addresses
+    fn write_addrs(&mut self, mut get_addr_val: impl FnMut() -> Option<(u32, u8)>) {
+        while let Some((addr, val)) = get_addr_val() {
+            self.sysbus.write_8(addr, val);
+        }
+    }
+
+    fn read_registers(&mut self, mut push_reg: impl FnMut(&[u8])) {
+        // general purpose registers
+        for i in 0..15 {
+            push_reg(&self.cpu.get_reg(i).to_le_bytes());
+        }
+        push_reg(&self.cpu.get_next_pc().to_le_bytes());
+        // Floating point registers, unused
+        for _ in 0..25 {
+            push_reg(&[0, 0, 0, 0]);
+        }
+        push_reg(&self.cpu.cpsr.get().to_le_bytes());
+    }
+
+    fn write_registers(&mut self, regs: &[u8]) {
+        let mut rdr = Cursor::new(regs);
+        for i in 0..15 {
+            self.cpu.set_reg(i, rdr.read_u32::<LittleEndian>().unwrap());
+        }
+        let new_pc = rdr.read_u32::<LittleEndian>().unwrap();
+        self.cpu.set_reg(15, new_pc);
+
+        self.cpu.cpsr.set(rdr.read_u32::<LittleEndian>().unwrap());
+
+        match self.cpu.cpsr.state() {
+            CpuState::ARM => self.cpu.reload_pipeline32(&mut self.sysbus),
+            CpuState::THUMB => self.cpu.reload_pipeline16(&mut self.sysbus),
+        };
+    }
+
+    fn target_description_xml() -> Option<&'static str> {
+        Some(
+            r#"
+        <target version="1.0">
+            <architecture>armv4t</architecture>
+        </target>"#,
+        )
+    }
+}

src/lib.rs

@@ -25,6 +25,9 @@ pub mod util;
 pub mod core;
 pub mod disass;
 
+#[cfg(feature = "gdb")]
+pub mod gdb;
+
 #[cfg(feature = "debugger")]
 pub mod debugger;
 
@@ -56,6 +59,7 @@ pub trait InputInterface {
 pub mod prelude {
     pub use super::core::arm7tdmi;
     pub use super::core::cartridge::GamepakBuilder;
+    pub use super::core::Bus;
     pub use super::core::{GBAError, GBAResult, GameBoyAdvance};
     #[cfg(feature = "debugger")]
     pub use super::debugger::Debugger;

src/plat/sdl2/cli.yml

@@ -29,7 +29,12 @@ args:
         help: Skip running bios and start from the ROM instead
     - debug:
         long: debug
-        help: Start with the debugger attached
+        help: Use the custom debugger
+    - with_gdbserver:
+        long: with-gdbserver
+        help: Start with experimental gdbserver
+        conflicts_with:
+            - debug
     - script_file:
         long: script-file
         short: f

src/plat/sdl2/main.rs

@@ -27,6 +27,9 @@ extern crate log;
 use flexi_logger;
 use flexi_logger::*;
 
+#[cfg(feature = "gdb")]
+use gdbstub;
+
 mod audio;
 mod input;
 mod video;
@@ -36,6 +39,8 @@ use input::create_input;
 use video::{create_video_interface, SCREEN_HEIGHT, SCREEN_WIDTH};
 
 use rustboyadvance_ng::core::cartridge::BackupType;
+#[cfg(feature = "gdb")]
+use rustboyadvance_ng::gdb::spawn_gdb_server;
 use rustboyadvance_ng::prelude::*;
 use rustboyadvance_ng::util::FpsCounter;
 
@@ -60,6 +65,29 @@ fn wait_for_rom(event_pump: &mut EventPump) -> String {
     }
 }
 
+fn spawn_and_run_gdb_server(gba: &mut GameBoyAdvance) -> Result<(), Box<dyn std::error::Error>> {
+    #[cfg(feature = "gdb")]
+    {
+        let mut gdb = spawn_gdb_server(format!("localhost:{}", 1337))?;
+        let result = match gdb.run(gba) {
+            Ok(state) => {
+                info!("Disconnected from GDB. Target state: {:?}", state);
+                Ok(())
+            }
+            Err(gdbstub::Error::TargetError(e)) => Err(e),
+            Err(e) => return Err(e.into()),
+        };
+
+        info!("Debugger session ended, result={:?}", result);
+    }
+    #[cfg(not(feature = "gdb"))]
+    {
+        error!("Please compile me with 'gdb' feature")
+    }
+
+    Ok(())
+}
+
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     fs::create_dir_all(LOG_DIR).expect(&format!("could not create log directory ({})", LOG_DIR));
     flexi_logger::Logger::with_env_or_str("info")
@@ -78,6 +106,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let skip_bios = matches.occurrences_of("skip_bios") != 0;
 
     let debug = matches.occurrences_of("debug") != 0;
+    let with_gdbserver = matches.occurrences_of("with_gdbserver") != 0;
 
     info!("Initializing SDL2 context");
     let sdl_context = sdl2::init().expect("failed to initialize sdl2");
@@ -161,6 +190,10 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         }
     }
 
+    if with_gdbserver {
+        spawn_and_run_gdb_server(&mut gba)?;
+    }
+
     let mut fps_counter = FpsCounter::default();
     let frame_time = time::Duration::new(0, 1_000_000_000u32 / 60);
     'running: loop {
@@ -192,6 +225,13 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                     info!("ending debugger...");
                     break;
                 }
+                #[cfg(feature = "gdb")]
+                Event::KeyUp {
+                    keycode: Some(Keycode::F2),
+                    ..
+                } => {
+                    spawn_and_run_gdb_server(&mut gba)?;
+                }
                 Event::KeyUp {
                     keycode: Some(Keycode::F5),
                     ..