src/emulator.rs

@@ -550,6 +550,13 @@ impl Emulator {
                 sim.read_memory(start, length, &mut buffer);
                 let _ = done.send(buffer);
             }
+            EmulatorCommand::WriteMemory(sim_id, start, buffer, done) => {
+                let Some(sim) = self.sims.get_mut(sim_id.to_index()) else {
+                    return;
+                };
+                sim.write_memory(start, &buffer);
+                let _ = done.send(buffer);
+            }
             EmulatorCommand::AddBreakpoint(sim_id, address) => {
                 let Some(sim) = self.sims.get_mut(sim_id.to_index()) else {
                     return;
@@ -639,6 +646,7 @@ pub enum EmulatorCommand {
     ReadRegister(SimId, VBRegister, oneshot::Sender<u32>),
     WriteRegister(SimId, VBRegister, u32),
     ReadMemory(SimId, u32, usize, Vec<u8>, oneshot::Sender<Vec<u8>>),
+    WriteMemory(SimId, u32, Vec<u8>, oneshot::Sender<Vec<u8>>),
     AddBreakpoint(SimId, u32),
     RemoveBreakpoint(SimId, u32),
     AddWatchpoint(SimId, u32, usize, VBWatchpointType),

src/emulator/shrooms_vb_core.rs

@@ -166,6 +166,8 @@ extern "C" {
     fn vb_set_write_callback(sim: *mut VB, callback: Option<OnWrite>) -> Option<OnWrite>;
     #[link_name = "vbSizeOf"]
     fn vb_size_of() -> usize;
+    #[link_name = "vbWrite"]
+    fn vb_write(sim: *mut VB, address: u32, _type: VBDataType, value: i32) -> i32;
 }
 
 extern "C" fn on_frame(sim: *mut VB) -> c_int {
@@ -476,6 +478,14 @@ impl Sim {
         }
     }
 
+    pub fn write_memory(&mut self, start: u32, buffer: &[u8]) {
+        let mut address = start;
+        for byte in buffer {
+            unsafe { vb_write(self.sim, address, VBDataType::U8, *byte as i32) };
+            address = address.wrapping_add(1);
+        }
+    }
+
     pub fn add_breakpoint(&mut self, address: u32) {
         let data = self.get_state();
         if let Err(index) = data.breakpoints.binary_search(&address) {

src/gdbserver.rs

@@ -346,22 +346,9 @@ impl GdbConnection {
             }
         } else if let Some(op) = req.match_some_str(["m", "x"]) {
             let mut read_memory = || {
-                let start = req.match_hex::<u64>()?;
-                if !req.match_str(",") {
-                    return None;
-                };
-                let length = req.match_hex::<usize>()?;
-
+                let (start, length) = parse_memory_range(&mut req)?;
                 let mut buf = self.memory_buf.take().unwrap_or_default();
                 buf.clear();
-
-                // The v810 has a 32-bit address space.
-                // Addresses wrap within that space, but we don't need to implement that for 64-bit addresses.
-                // Just refuse to return any info for addresses above 0xffffffff.
-                let Ok(start) = u32::try_from(start) else {
-                    return Some(buf);
-                };
-                let length = length.min((u32::MAX - start) as usize + 1);
                 if length == 0 {
                     return Some(buf);
                 }
@@ -395,6 +382,38 @@ impl GdbConnection {
             } else {
                 self.response()
             }
+        } else if let Some(op) = req.match_some_str(["M", "X"]) {
+            let mut write_memory = || {
+                let (start, length) = parse_memory_range(&mut req)?;
+                if length == 0 {
+                    return Some(());
+                }
+                if !req.match_str(":") {
+                    return None;
+                }
+                let mut buf = self.memory_buf.take().unwrap_or_default();
+                buf.resize(length, 0);
+                let successful_read = if op == "M" {
+                    req.match_hex_bytes(&mut buf)
+                } else {
+                    req.match_bytes(&mut buf)
+                };
+                if !successful_read {
+                    self.memory_buf = Some(buf);
+                    return None;
+                }
+                let (tx, rx) = ::oneshot::channel();
+                self.client
+                    .send_command(EmulatorCommand::WriteMemory(self.sim_id, start, buf, tx));
+                let buf = rx.recv().ok()?;
+                self.memory_buf = Some(buf);
+                Some(())
+            };
+            if write_memory().is_some() {
+                self.response().write_str("OK")
+            } else {
+                self.response()
+            }
         } else if req.match_str("Z") {
             let mut parse_request = || {
                 let type_ = req.match_hex::<u8>()?;
@@ -483,6 +502,23 @@ impl Drop for GdbConnection {
     }
 }
 
+// parse a memory range into a start and a length.
+fn parse_memory_range(req: &mut Request<'_>) -> Option<(u32, usize)> {
+    let start = req.match_hex::<u64>()?;
+    if !req.match_str(",") {
+        return None;
+    };
+    let length = req.match_hex::<usize>()?;
+    let Ok(start) = u32::try_from(start) else {
+        // The v810 has a 32-bit address space.
+        // Addresses wrap within that space, but we don't need to implement that for 64-bit addresses.
+        // Just refuse to return any info for addresses above 0xffffffff.
+        return Some((0, 0));
+    };
+    let length = length.min((u32::MAX - start) as usize + 1);
+    Some((start, length))
+}
+
 fn debug_stop_reason_string(reason: Option<DebugStopReason>) -> String {
     let mut result = String::new();
     result += if reason.is_some() { "T05;" } else { "T00;" };

src/gdbserver/request.rs

@@ -74,6 +74,15 @@ impl Request<'_> {
         self.buffer = self.buffer.split_at(buffer.len()).1;
         true
     }
+
+    pub fn match_bytes(&mut self, buffer: &mut [u8]) -> bool {
+        if self.buffer.len() < buffer.len() {
+            return false;
+        }
+        buffer.copy_from_slice(&self.buffer[0..buffer.len()]);
+        self.buffer = self.buffer.split_at(buffer.len()).1;
+        true
+    }
 }
 
 pub struct RequestSource<R> {