BloomPatched/src/DebugServer/Gdb/AvrGdb/CommandPackets/ReadMemory.cpp

#include "ReadMemory.hpp"

#include "src/DebugServer/Gdb/ResponsePackets/ErrorResponsePacket.hpp"
#include "src/DebugServer/Gdb/ResponsePackets/ResponsePacket.hpp"

#include "src/Logger/Logger.hpp"
#include "src/Exceptions/Exception.hpp"

namespace Bloom::DebugServer::Gdb::AvrGdb::CommandPackets
{
    using TargetController::TargetControllerConsole;

    using ResponsePackets::ErrorResponsePacket;
    using ResponsePackets::ResponsePacket;

    using Exceptions::Exception;

    ReadMemory::ReadMemory(const RawPacketType& rawPacket)
        : MemoryAccessCommandPacket(rawPacket)
    {
        if (this->data.size() < 4) {
            throw Exception("Invalid packet length");
        }

        auto packetString = QString::fromLocal8Bit(
            reinterpret_cast<const char*>(this->data.data() + 1),
            static_cast<int>(this->data.size() - 1)
        );

        /*
         * The read memory ('m') packet consists of two segments, an address and a number of bytes to read.
         * These are separated by a comma character.
         */
        auto packetSegments = packetString.split(",");

        if (packetSegments.size() != 2) {
            throw Exception(
                "Unexpected number of segments in packet data: " + std::to_string(packetSegments.size())
            );
        }

        bool conversionStatus = false;
        const auto gdbStartAddress = packetSegments.at(0).toUInt(&conversionStatus, 16);

        if (!conversionStatus) {
            throw Exception("Failed to parse start address from read memory packet data");
        }

        this->memoryType = this->getMemoryTypeFromGdbAddress(gdbStartAddress);
        this->startAddress = this->removeMemoryTypeIndicatorFromGdbAddress(gdbStartAddress);

        this->bytes = packetSegments.at(1).toUInt(&conversionStatus, 16);

        if (!conversionStatus) {
            throw Exception("Failed to parse read length from read memory packet data");
        }
    }

    void ReadMemory::handle(DebugSession& debugSession, TargetControllerConsole& targetControllerConsole) {
        Logger::debug("Handling ReadMemory packet");

        try {
            const auto& memoryDescriptorsByType = debugSession.gdbTargetDescriptor.targetDescriptor.memoryDescriptorsByType;

            if (!memoryDescriptorsByType.contains(this->memoryType)) {
                throw Exception("Target does not support the requested memory type.");
            }

            if (this->bytes == 0) {
                debugSession.connection.writePacket(
                    ResponsePacket(std::vector<unsigned char>())
                );
                return;
            }

            const auto& memoryDescriptor = memoryDescriptorsByType.at(this->memoryType);

            if (
                this->startAddress < memoryDescriptor.addressRange.startAddress
                || (this->startAddress + (this->bytes - 1)) > memoryDescriptor.addressRange.endAddress
            ) {
                /*
                 * GDB can be configured to generate backtraces past the main function and the internal entry point
                 * of the application. Although this isn't very useful to most devs, CLion now seems to enable it by
                 * default. Somewhere between CLion 2021.1 and 2022.1, it began issuing the "-gdb-set backtrace past-entry on"
                 * command to GDB, at the beginning of each debug session.
                 *
                 * This means that GDB will attempt to walk down the stack to identify every frame. The problem is that
                 * GDB doesn't really know where the stack begins, so it ends up in a loop, continually issuing read
                 * memory commands. This has exposed an issue on our end - we need to validate the requested memory
                 * address range and reject any request for a range that's not within the target's memory. We do this
                 * here.
                 *
                 * We don't throw an exception here, because this isn't really an error and so it's best not to report
                 * it as such. I don't think it's an error because it's expected behaviour, even though we respond to
                 * GDB with an error response.
                 */
                Logger::debug(
                    "GDB requested access to memory which is outside the target's memory range - returning error response"
                );
                debugSession.connection.writePacket(ErrorResponsePacket());
                return;
            }

            auto memoryBuffer = targetControllerConsole.readMemory(
                this->memoryType,
                this->startAddress,
                this->bytes
            );

            debugSession.connection.writePacket(
                ResponsePacket(Packet::toHex(memoryBuffer))
            );

        } catch (const Exception& exception) {
            Logger::error("Failed to read memory from target - " + exception.getMessage());
            debugSession.connection.writePacket(ErrorResponsePacket());
        }
    }
}