track deleted breakpoints to handle stale events safely

GleeBug/Debugger.Loop.Exception.cpp

@@ -21,17 +21,14 @@ namespace GleeBug
             }
             else
             {
-                //check if this was a deleted breakpoint
-                //if the byte at the exception address is not 0xCC, our breakpoint was deleted
-                //and we should set IP back and continue execution
-                uint8 currentByte = 0xCC;
-                if(mThread && mProcess->MemReadUnsafe(exceptionAddress, &currentByte, 1) && currentByte != 0xCC)
+                //check if this address had a breakpoint that was recently deleted
+                auto& deletedBps = mProcess->recentlyDeletedSwbp;
+                auto foundIt = std::find(deletedBps.begin(), deletedBps.end(), exceptionAddress);
+                if(foundIt != deletedBps.end() && mThread)
                 {
-                    //this was our deleted breakpoint, set IP back and continue
                     Registers(mThread->hThread, CONTEXT_CONTROL).Gip = exceptionAddress;
                     mContinueStatus = DBG_CONTINUE;
                 }
-                //else: byte is 0xCC, this is a real int3 in original code, let debuggee handle it
             }
             return;
         }

GleeBug/Debugger.Loop.cpp

@@ -40,6 +40,8 @@ namespace GleeBug
             IsDbgReplyLaterSupported = mSafeStep;
         }
 
+        uint32 consecutiveTimeouts = 0;
+
         while(!mBreakDebugger)
         {
             //wait for a debug event
@@ -65,11 +67,18 @@ namespace GleeBug
 #endif
                 else
                 {
-                    // Regular timeout, wait again
+                    //after 2 consecutive timeouts, clear recently deleted breakpoints
+                    //any stale events would have been delivered by now
+                    consecutiveTimeouts++;
+                    if(consecutiveTimeouts >= 2 && mProcess)
+                        mProcess->recentlyDeletedSwbp.clear();
                     continue;
                 }
             }
 
+            //event received, reset timeout counter
+            consecutiveTimeouts = 0;
+
             // Handle safe stepping
             if(IsDbgReplyLaterSupported)
             {

GleeBug/Debugger.Process.Breakpoint.cpp

@@ -68,6 +68,8 @@ namespace GleeBug
             return false;
         FlushInstructionCache(hProcess, nullptr, 0);
 
+        recentlyDeletedSwbp.push_back(address);
+
         //remove the breakpoint from the maps
         softwareBreakpointReferences.erase(info.address);
         breakpoints.erase(found);

GleeBug/Debugger.Process.h

@@ -32,6 +32,8 @@ namespace GleeBug
         MemoryBreakpointSet memoryBreakpointRanges;
         MemoryBreakpointMap memoryBreakpointPages;
 
+        std::vector<ptr> recentlyDeletedSwbp;
+
         /**
         \brief Constructor.
         \param hProcess Process handle.