Update existing breakpoint instead of overwriting (#874)

src/agent/debugger/src/breakpoint.rs

@@ -103,6 +103,11 @@ impl ResolvedBreakpoint {
         self.kind
     }
 
+    pub fn update(&mut self, id: BreakpointId, kind: BreakpointType) {
+        self.id = id;
+        self.kind = kind;
+    }
+
     #[allow(unused)]
     pub fn is_enabled(&self) -> bool {
         !self.is_disabled()
@@ -119,10 +124,8 @@ impl ResolvedBreakpoint {
     pub(crate) fn disable(&mut self, process_handle: HANDLE) -> Result<()> {
         self.disabled = self.disabled.saturating_add(1);
 
-        if self.is_disabled() {
-            if let Some(original_byte) = self.original_byte.take() {
-                write_instruction_byte(process_handle, self.address, original_byte)?;
-            }
+        if let Some(original_byte) = self.original_byte.take() {
+            write_instruction_byte(process_handle, self.address, original_byte)?;
         }
 
         Ok(())
@@ -131,9 +134,10 @@ impl ResolvedBreakpoint {
     pub fn enable(&mut self, process_handle: HANDLE) -> Result<()> {
         self.disabled = self.disabled.saturating_sub(1);
 
-        let new_original_byte = process::read_memory(process_handle, self.address as _)?;
-        self.original_byte = Some(new_original_byte);
-        write_instruction_byte(process_handle, self.address, 0xcc)?;
+        if self.original_byte.is_none() {
+            self.original_byte = Some(process::read_memory(process_handle, self.address as _)?);
+            write_instruction_byte(process_handle, self.address, 0xcc)?;
+        }
 
         Ok(())
     }

src/agent/debugger/src/module.rs

@@ -117,9 +117,21 @@ impl Module {
         address: u64,
         process_handle: HANDLE,
     ) -> Result<()> {
-        let mut breakpoint = ResolvedBreakpoint::new(id, kind, address);
-        breakpoint.enable(process_handle)?;
-        self.breakpoints.insert(address, breakpoint);
+        if let Some(breakpoint) = self.breakpoints.get_mut(address) {
+            // Update the existing breakpoint with a (probably new) id and (probably not new) kind.
+            breakpoint.update(id, kind);
+            if breakpoint.is_disabled() {
+                // Existing breakpoint was disabled, but the caller wants a new
+                // breakpoint that by luck or otherwise, was at the same address
+                // as an existing breakpoint, so we go ahead and enable.
+                breakpoint.enable(process_handle)?;
+            }
+        } else {
+            let mut breakpoint = ResolvedBreakpoint::new(id, kind, address);
+            breakpoint.enable(process_handle)?;
+            self.breakpoints.insert(address, breakpoint);
+        }
+
         Ok(())
     }