4 files changed, 274 insertions, 0 deletions

diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index d65659b44..cb77b99ee 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -476,6 +476,8 @@ add_library(core STATIC
     settings.h
     telemetry_session.cpp
     telemetry_session.h
+    tools/freezer.cpp
+    tools/freezer.h
 )
 
 create_target_directory_groups(core)
diff --git a/src/core/core.cpp b/src/core/core.cpp
index df26eb109..262411db8 100644
--- a/src/core/core.cpp
+++ b/src/core/core.cpp
@@ -33,6 +33,7 @@
 #include "core/reporter.h"
 #include "core/settings.h"
 #include "core/telemetry_session.h"
+#include "core/tools/freezer.h"
 #include "file_sys/cheat_engine.h"
 #include "file_sys/patch_manager.h"
 #include "video_core/debug_utils/debug_utils.h"
@@ -300,6 +301,7 @@ struct System::Impl {
     bool is_powered_on = false;
 
     std::unique_ptr<FileSys::CheatEngine> cheat_engine;
+    std::unique_ptr<Tools::Freezer> memory_freezer;
 
     /// Frontend applets
     Service::AM::Applets::AppletManager applet_manager;
diff --git a/src/core/tools/freezer.cpp b/src/core/tools/freezer.cpp
new file mode 100644
index 000000000..17f050068
--- /dev/null
+++ b/src/core/tools/freezer.cpp
@@ -0,0 +1,188 @@
+// Copyright 2019 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "common/assert.h"
+#include "common/logging/log.h"
+#include "core/core.h"
+#include "core/core_timing.h"
+#include "core/core_timing_util.h"
+#include "core/memory.h"
+#include "core/tools/freezer.h"
+
+namespace Tools {
+
+namespace {
+
+constexpr s64 MEMORY_FREEZER_TICKS = static_cast<s64>(Core::Timing::BASE_CLOCK_RATE / 60);
+
+u64 MemoryReadWidth(u32 width, VAddr addr) {
+    switch (width) {
+    case 1:
+        return Memory::Read8(addr);
+    case 2:
+        return Memory::Read16(addr);
+    case 4:
+        return Memory::Read32(addr);
+    case 8:
+        return Memory::Read64(addr);
+    default:
+        UNREACHABLE();
+        return 0;
+    }
+}
+
+void MemoryWriteWidth(u32 width, VAddr addr, u64 value) {
+    switch (width) {
+    case 1:
+        Memory::Write8(addr, static_cast<u8>(value));
+        break;
+    case 2:
+        Memory::Write16(addr, static_cast<u16>(value));
+        break;
+    case 4:
+        Memory::Write32(addr, static_cast<u32>(value));
+        break;
+    case 8:
+        Memory::Write64(addr, value);
+        break;
+    default:
+        UNREACHABLE();
+    }
+}
+
+} // Anonymous namespace
+
+Freezer::Freezer(Core::Timing::CoreTiming& core_timing) : core_timing(core_timing) {
+    event = core_timing.RegisterEvent(
+        "MemoryFreezer::FrameCallback",
+        [this](u64 userdata, s64 cycles_late) { FrameCallback(userdata, cycles_late); });
+    core_timing.ScheduleEvent(MEMORY_FREEZER_TICKS, event);
+}
+
+Freezer::~Freezer() {
+    core_timing.UnscheduleEvent(event, 0);
+}
+
+void Freezer::SetActive(bool active) {
+    if (!this->active.exchange(active)) {
+        FillEntryReads();
+        core_timing.ScheduleEvent(MEMORY_FREEZER_TICKS, event);
+        LOG_DEBUG(Common_Memory, "Memory freezer activated!");
+    } else {
+        LOG_DEBUG(Common_Memory, "Memory freezer deactivated!");
+    }
+}
+
+bool Freezer::IsActive() const {
+    return active.load(std::memory_order_relaxed);
+}
+
+void Freezer::Clear() {
+    std::lock_guard lock{entries_mutex};
+
+    LOG_DEBUG(Common_Memory, "Clearing all frozen memory values.");
+
+    entries.clear();
+}
+
+u64 Freezer::Freeze(VAddr address, u32 width) {
+    std::lock_guard lock{entries_mutex};
+
+    const auto current_value = MemoryReadWidth(width, address);
+    entries.push_back({address, width, current_value});
+
+    LOG_DEBUG(Common_Memory,
+              "Freezing memory for address={:016X}, width={:02X}, current_value={:016X}", address,
+              width, current_value);
+
+    return current_value;
+}
+
+void Freezer::Unfreeze(VAddr address) {
+    std::lock_guard lock{entries_mutex};
+
+    LOG_DEBUG(Common_Memory, "Unfreezing memory for address={:016X}", address);
+
+    entries.erase(
+        std::remove_if(entries.begin(), entries.end(),
+                       [&address](const Entry& entry) { return entry.address == address; }),
+        entries.end());
+}
+
+bool Freezer::IsFrozen(VAddr address) const {
+    std::lock_guard lock{entries_mutex};
+
+    return std::find_if(entries.begin(), entries.end(), [&address](const Entry& entry) {
+               return entry.address == address;
+           }) != entries.end();
+}
+
+void Freezer::SetFrozenValue(VAddr address, u64 value) {
+    std::lock_guard lock{entries_mutex};
+
+    const auto iter = std::find_if(entries.begin(), entries.end(), [&address](const Entry& entry) {
+        return entry.address == address;
+    });
+
+    if (iter == entries.end()) {
+        LOG_ERROR(Common_Memory,
+                  "Tried to set freeze value for address={:016X} that is not frozen!", address);
+        return;
+    }
+
+    LOG_DEBUG(Common_Memory,
+              "Manually overridden freeze value for address={:016X}, width={:02X} to value={:016X}",
+              iter->address, iter->width, value);
+    iter->value = value;
+}
+
+std::optional<Freezer::Entry> Freezer::GetEntry(VAddr address) const {
+    std::lock_guard lock{entries_mutex};
+
+    const auto iter = std::find_if(entries.begin(), entries.end(), [&address](const Entry& entry) {
+        return entry.address == address;
+    });
+
+    if (iter == entries.end()) {
+        return std::nullopt;
+    }
+
+    return *iter;
+}
+
+std::vector<Freezer::Entry> Freezer::GetEntries() const {
+    std::lock_guard lock{entries_mutex};
+
+    return entries;
+}
+
+void Freezer::FrameCallback(u64 userdata, s64 cycles_late) {
+    if (!IsActive()) {
+        LOG_DEBUG(Common_Memory, "Memory freezer has been deactivated, ending callback events.");
+        return;
+    }
+
+    std::lock_guard lock{entries_mutex};
+
+    for (const auto& entry : entries) {
+        LOG_DEBUG(Common_Memory,
+                  "Enforcing memory freeze at address={:016X}, value={:016X}, width={:02X}",
+                  entry.address, entry.value, entry.width);
+        MemoryWriteWidth(entry.width, entry.address, entry.value);
+    }
+
+    core_timing.ScheduleEvent(MEMORY_FREEZER_TICKS - cycles_late, event);
+}
+
+void Freezer::FillEntryReads() {
+    std::lock_guard lock{entries_mutex};
+
+    LOG_DEBUG(Common_Memory, "Updating memory freeze entries to current values.");
+
+    for (auto& entry : entries) {
+        entry.value = MemoryReadWidth(entry.width, entry.address);
+    }
+}
+
+} // namespace Tools
diff --git a/src/core/tools/freezer.h b/src/core/tools/freezer.h
new file mode 100644
index 000000000..b58de5472
--- /dev/null
+++ b/src/core/tools/freezer.h
@@ -0,0 +1,82 @@
+// Copyright 2019 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <atomic>
+#include <mutex>
+#include <optional>
+#include <vector>
+#include "common/common_types.h"
+
+namespace Core::Timing {
+class CoreTiming;
+struct EventType;
+} // namespace Core::Timing
+
+namespace Tools {
+
+/**
+ * This class allows the user to prevent an application from writing new values to certain memory
+ * locations. This has a variety of uses when attempting to reverse a game.
+ *
+ * One example could be a cheat to prevent Mario from taking damage in SMO. One could freeze the
+ * memory address that the game uses to store Mario's health so when he takes damage (and the game
+ * tries to write the new health value to memory), the value won't change.
+ */
+class Freezer {
+public:
+    struct Entry {
+        VAddr address;
+        u32 width;
+        u64 value;
+    };
+
+    explicit Freezer(Core::Timing::CoreTiming& core_timing);
+    ~Freezer();
+
+    // Enables or disables the entire memory freezer.
+    void SetActive(bool active);
+
+    // Returns whether or not the freezer is active.
+    bool IsActive() const;
+
+    // Removes all entries from the freezer.
+    void Clear();
+
+    // Freezes a value to its current memory address. The value the memory is kept at will be the
+    // value that is read during this function. Width can be 1, 2, 4, or 8 (in bytes).
+    u64 Freeze(VAddr address, u32 width);
+
+    // Unfreezes the memory value at address. If the address isn't frozen, this is a no-op.
+    void Unfreeze(VAddr address);
+
+    // Returns whether or not the address is frozen.
+    bool IsFrozen(VAddr address) const;
+
+    // Sets the value that address should be frozen to. This doesn't change the width set by using
+    // Freeze(). If the value isn't frozen, this will not freeze it and is thus a no-op.
+    void SetFrozenValue(VAddr address, u64 value);
+
+    // Returns the entry corresponding to the address if the address is frozen, otherwise
+    // std::nullopt.
+    std::optional<Entry> GetEntry(VAddr address) const;
+
+    // Returns all the entries in the freezer, an empty vector means nothing is frozen.
+    std::vector<Entry> GetEntries() const;
+
+private:
+    void FrameCallback(u64 userdata, s64 cycles_late);
+    void FillEntryReads();
+
+    std::atomic_bool active{false};
+
+    mutable std::mutex entries_mutex;
+    std::vector<Entry> entries;
+
+    Core::Timing::EventType* event;
+    Core::Timing::CoreTiming& core_timing;
+};
+
+} // namespace Tools