Implemented support for breakpoint caching in the GDB server

src/DebugServer/Gdb/AvrGdb/AvrGdbRsp.cpp

@@ -29,6 +29,13 @@ namespace Bloom::DebugServer::Gdb::AvrGdb
         this->gdbTargetDescriptor = TargetDescriptor(
             this->targetControllerService.getTargetDescriptor()
         );
+
+        if (!this->debugServerConfig.breakpointCachingEnabled) {
+            Logger::warning(
+                "Breakpoint caching has been disabled - this could result in excessive wear of the AVR target's"
+                " flash memory"
+            );
+        }
     }
 
     std::unique_ptr<Gdb::CommandPackets::CommandPacket> AvrGdbRsp::resolveCommandPacket(

src/DebugServer/Gdb/CommandPackets/CommandPacket.hpp

@@ -36,7 +36,13 @@ namespace Bloom::DebugServer::Gdb::CommandPackets
     class CommandPacket: public Packet
     {
     public:
-        explicit CommandPacket(const RawPacket& rawPacket): Packet(rawPacket) {}
+        explicit CommandPacket(const RawPacket& rawPacket)
+            : Packet(rawPacket)
+        {}
+
+        virtual bool requiresBreakpointFlush() const {
+            return false;
+        }
 
         /**
          * Should handle the command for the current active debug session.

src/DebugServer/Gdb/CommandPackets/ContinueExecution.hpp

@@ -28,6 +28,10 @@ namespace Bloom::DebugServer::Gdb::CommandPackets
 
         explicit ContinueExecution(const RawPacket& rawPacket);
 
+        bool requiresBreakpointFlush() const override {
+            return true;
+        }
+
         void handle(
             DebugSession& debugSession,
             Services::TargetControllerService& targetControllerService

src/DebugServer/Gdb/CommandPackets/Detach.hpp

@@ -9,6 +9,10 @@ namespace Bloom::DebugServer::Gdb::CommandPackets
     public:
         explicit Detach(const RawPacket& rawPacket);
 
+        bool requiresBreakpointFlush() const override {
+            return true;
+        }
+
         void handle(
             DebugSession& debugSession,
             Services::TargetControllerService& targetControllerService

src/DebugServer/Gdb/CommandPackets/RemoveBreakpoint.cpp

@@ -51,9 +51,18 @@ namespace Bloom::DebugServer::Gdb::CommandPackets
     }
 
     void RemoveBreakpoint::handle(DebugSession& debugSession, TargetControllerService& targetControllerService) {
-        Logger::debug("Removing breakpoint at address " + std::to_string(this->address));
+        Logger::debug("Handling RemoveBreakpoint packet");
 
         try {
+            if (debugSession.serverConfig.breakpointCachingEnabled) {
+                debugSession.breakpointAddressesPendingRemoval.insert(this->address);
+                debugSession.connection.writePacket(OkResponsePacket());
+
+                return;
+            }
+
+            Logger::debug("Removing breakpoint at address " + std::to_string(this->address));
+
             targetControllerService.removeBreakpoint(TargetBreakpoint(this->address));
             debugSession.connection.writePacket(OkResponsePacket());
 

src/DebugServer/Gdb/CommandPackets/SetBreakpoint.cpp

@@ -54,7 +54,18 @@ namespace Bloom::DebugServer::Gdb::CommandPackets
         Logger::debug("Handling SetBreakpoint packet");
 
         try {
+            if (
+                !debugSession.serverConfig.breakpointCachingEnabled
+                || !debugSession.breakpointAddresses.contains(this->address)
+            ) {
                 targetControllerService.setBreakpoint(TargetBreakpoint(this->address));
+            }
+
+            if (debugSession.serverConfig.breakpointCachingEnabled) {
+                debugSession.breakpointAddresses.insert(this->address);
+                debugSession.breakpointAddressesPendingRemoval.erase(this->address);
+            }
+
             debugSession.connection.writePacket(OkResponsePacket());
 
         } catch (const Exception& exception) {

src/DebugServer/Gdb/CommandPackets/StepExecution.hpp

@@ -23,6 +23,10 @@ namespace Bloom::DebugServer::Gdb::CommandPackets
 
         explicit StepExecution(const RawPacket& rawPacket);
 
+        bool requiresBreakpointFlush() const override {
+            return false;
+        }
+
         void handle(
             DebugSession& debugSession,
             Services::TargetControllerService& targetControllerService

src/DebugServer/Gdb/DebugSession.cpp

@@ -7,11 +7,13 @@ namespace Bloom::DebugServer::Gdb
     DebugSession::DebugSession(
         Connection&& connection,
         const std::set<std::pair<Feature, std::optional<std::string>>>& supportedFeatures,
-        const TargetDescriptor& targetDescriptor
+        const TargetDescriptor& targetDescriptor,
+        const GdbDebugServerConfig& serverConfig
     )
         : connection(std::move(connection))
         , supportedFeatures(supportedFeatures)
         , gdbTargetDescriptor(targetDescriptor)
+        , serverConfig(serverConfig)
     {
         this->supportedFeatures.insert({
             Feature::PACKET_SIZE, std::to_string(Connection::ABSOLUTE_MAXIMUM_PACKET_READ_SIZE)

src/DebugServer/Gdb/DebugSession.hpp

@@ -2,12 +2,16 @@
 
 #include <cstdint>
 #include <optional>
+#include <unordered_set>
 
 #include "TargetDescriptor.hpp"
+#include "GdbDebugServerConfig.hpp"
 #include "Connection.hpp"
 #include "Feature.hpp"
 #include "ProgrammingSession.hpp"
 
+#include "src/Targets/TargetMemory.hpp"
+
 namespace Bloom::DebugServer::Gdb
 {
     class DebugSession
@@ -29,6 +33,18 @@ namespace Bloom::DebugServer::Gdb
          */
         const TargetDescriptor& gdbTargetDescriptor;
 
+        /**
+         * The current server configuration.
+         */
+        const GdbDebugServerConfig& serverConfig;
+
+        /**
+         * Internal bookkeeping of breakpoints managed by GDB. These will both remain empty if the user has disabled
+         * breakpoint caching.
+         */
+        std::unordered_set<Targets::TargetMemoryAddress> breakpointAddresses;
+        std::unordered_set<Targets::TargetMemoryAddress> breakpointAddressesPendingRemoval;
+
         /**
          * When the GDB client is waiting for the target to halt, this is set to true so we know when to notify the
          * client.
@@ -53,7 +69,8 @@ namespace Bloom::DebugServer::Gdb
         DebugSession(
             Connection&& connection,
             const std::set<std::pair<Feature, std::optional<std::string>>>& supportedFeatures,
-            const TargetDescriptor& targetDescriptor
+            const TargetDescriptor& targetDescriptor,
+            const GdbDebugServerConfig& serverConfig
         );
 
         DebugSession(const DebugSession& other) = delete;

src/DebugServer/Gdb/GdbDebugServerConfig.cpp

@@ -30,5 +30,17 @@ namespace Bloom::DebugServer::Gdb
                 );
             }
         }
+
+        if (debugServerConfig.debugServerNode["enableBreakpointCaching"]) {
+            if (YamlUtilities::isCastable<bool>(debugServerConfig.debugServerNode["enableBreakpointCaching"])) {
+                this->breakpointCachingEnabled = debugServerConfig.debugServerNode["enableBreakpointCaching"].as<bool>();
+
+            } else {
+                Logger::error(
+                    "Invalid GDB debug server config parameter ('enableBreakpointCaching') provided - value must be "
+                    "castable to a boolean. The parameter will be ignored."
+                );
+            }
+        }
     }
 }

src/DebugServer/Gdb/GdbDebugServerConfig.hpp

@@ -24,6 +24,19 @@ namespace Bloom::DebugServer::Gdb
          */
         std::string listeningAddress = "127.0.0.1";
 
+        /**
+         * GDB tends to remove all breakpoints when target execution stops, and then installs them again, just before
+         * resuming target execution. This can result in excessive wearing of the target's program memory, as well as
+         * a negative impact on performance.
+         *
+         * When breakpoint caching is enabled, Bloom's GDB server will perform internal bookkeeping of the breakpoints
+         * installed and removed via GDB. Then, just before resuming target execution, it will only apply the necessary
+         * changes to the target, avoiding the excessive wear and IO.
+         *
+         * This param is optional, and is enabled by default.
+         */
+        bool breakpointCachingEnabled = true;
+
         explicit GdbDebugServerConfig(const DebugServerConfig& debugServerConfig);
     };
 }

src/DebugServer/Gdb/GdbRspDebugServer.cpp

@@ -154,7 +154,8 @@ namespace Bloom::DebugServer::Gdb
                 this->activeDebugSession.emplace(
                     std::move(connection),
                     this->getSupportedFeatures(),
-                    this->getGdbTargetDescriptor()
+                    this->getGdbTargetDescriptor(),
+                    this->debugServerConfig
                 );
 
                 /*
@@ -183,6 +184,10 @@ namespace Bloom::DebugServer::Gdb
             const auto commandPacket = this->waitForCommandPacket();
 
             if (commandPacket) {
+                if (this->debugServerConfig.breakpointCachingEnabled && commandPacket->requiresBreakpointFlush()) {
+                    this->flushBreakpointRemovals();
+                }
+
                 commandPacket->handle(this->activeDebugSession.value(), this->targetControllerService);
             }
 
@@ -367,4 +372,28 @@ namespace Bloom::DebugServer::Gdb
             return;
         }
     }
+
+    void GdbRspDebugServer::flushBreakpointRemovals() {
+        Logger::debug(
+            "Removing " + std::to_string(this->activeDebugSession->breakpointAddressesPendingRemoval.size())
+            + " breakpoint(s)"
+        );
+
+        for (const auto& breakpointAddress : this->activeDebugSession->breakpointAddressesPendingRemoval) {
+            try {
+                Logger::debug("Removing breakpoint at address " + std::to_string(breakpointAddress));
+
+                this->targetControllerService.removeBreakpoint(Targets::TargetBreakpoint(breakpointAddress));
+                this->activeDebugSession->breakpointAddresses.erase(breakpointAddress);
+
+            } catch (const Exception& exception) {
+                Logger::error(
+                    "Failed to remove breakpoint at address " + std::to_string(breakpointAddress) + " from target - "
+                    + exception.getMessage()
+                );
+            }
+        }
+
+        this->activeDebugSession->breakpointAddressesPendingRemoval.clear();
+    }
 }

src/DebugServer/Gdb/GdbRspDebugServer.hpp

@@ -197,5 +197,10 @@ namespace Bloom::DebugServer::Gdb
          * a "stop reply" packet to the client once the target execution stops.
          */
         void onTargetExecutionStopped(const Events::TargetExecutionStopped&);
+
+        /**
+         * Actions any pending breakpoint removals.
+         */
+        void flushBreakpointRemovals();
     };
 }