From b9388935990c80c4ef35f33650ef236ffb39217c Mon Sep 17 00:00:00 2001
From: Zephyron <zephyron@citron-emu.org>
Date: Sat, 18 Jan 2025 15:19:45 +1000
Subject: memory: Improve null pointer and unmapped memory handling

- Update vcpkg baseline to a42af01b72c28a8e1d7b48107b33e4f286a55ef6
- Add SPIRV-Tools and SPIRV-Headers as submodules
- Update Vulkan-related submodules to latest stable versions
- Improve memory access error handling:
  - Add specific handling for null pointer accesses in ARM32 emulation
  - Return 0 for null pointer reads instead of undefined behavior
  - Silently ignore writes to null pointers
  - Add more detailed error messages distinguishing between null pointer
    access and other unmapped memory errors
  - Treat addresses below 0x1000 as potential null pointer accesses

These changes should provide more graceful handling of null pointer
accesses and improve stability when running games that attempt invalid
memory operations.
---
 src/core/arm/dynarmic/arm_dynarmic_32.cpp |  7 +++++++
 src/core/memory.cpp                       | 16 ++++++++++++++++
 2 files changed, 23 insertions(+)

(limited to 'src')

diff --git a/src/core/arm/dynarmic/arm_dynarmic_32.cpp b/src/core/arm/dynarmic/arm_dynarmic_32.cpp
index 36478f722..28d062e7a 100644
--- a/src/core/arm/dynarmic/arm_dynarmic_32.cpp
+++ b/src/core/arm/dynarmic/arm_dynarmic_32.cpp
@@ -95,6 +95,13 @@ public:
             LOG_CRITICAL(Core_ARM, "Cannot execute instruction at unmapped address {:#08x}", pc);
             ReturnException(pc, PrefetchAbort);
             return;
+        case Dynarmic::A32::Exception::AccessViolation:
+            if (pc == 0 || pc < 0x1000) {
+                LOG_CRITICAL(Core_ARM, "Null pointer dereference at {:#08x}", pc);
+                ReturnException(pc, DataAbort);
+                return;
+            }
+            [[fallthrough]];
         default:
             if (m_debugger_enabled) {
                 ReturnException(pc, InstructionBreakpoint);
diff --git a/src/core/memory.cpp b/src/core/memory.cpp
index 62437415b..4e9c58718 100644
--- a/src/core/memory.cpp
+++ b/src/core/memory.cpp
@@ -737,12 +737,21 @@ struct Memory::Impl {
         const u8* const ptr = GetPointerImpl(
             GetInteger(vaddr),
             [vaddr]() {
+                // Add special handling for null pointer reads
+                if (GetInteger(vaddr) == 0 || GetInteger(vaddr) < 0x1000) {
+                    LOG_ERROR(HW_Memory, "Null pointer Read{} @ 0x{:016X}", sizeof(T) * 8,
+                              GetInteger(vaddr));
+                    return;
+                }
                 LOG_ERROR(HW_Memory, "Unmapped Read{} @ 0x{:016X}", sizeof(T) * 8,
                           GetInteger(vaddr));
             },
             [&]() { HandleRasterizerDownload(GetInteger(vaddr), sizeof(T)); });
         if (ptr) {
             std::memcpy(&result, ptr, sizeof(T));
+        } else if (GetInteger(vaddr) == 0) {
+            // Return 0 for null pointer reads instead of random memory
+            result = 0;
         }
         return result;
     }
@@ -761,6 +770,12 @@ struct Memory::Impl {
         u8* const ptr = GetPointerImpl(
             GetInteger(vaddr),
             [vaddr, data]() {
+                // Add special handling for null pointer writes
+                if (GetInteger(vaddr) == 0 || GetInteger(vaddr) < 0x1000) {
+                    LOG_ERROR(HW_Memory, "Null pointer Write{} @ 0x{:016X} = 0x{:016X}", sizeof(T) * 8,
+                              GetInteger(vaddr), static_cast<u64>(data));
+                    return;
+                }
                 LOG_ERROR(HW_Memory, "Unmapped Write{} @ 0x{:016X} = 0x{:016X}", sizeof(T) * 8,
                           GetInteger(vaddr), static_cast<u64>(data));
             },
@@ -768,6 +783,7 @@ struct Memory::Impl {
         if (ptr) {
             std::memcpy(ptr, &data, sizeof(T));
         }
+        // Silently ignore writes to null pointer
     }
 
     template <typename T>
-- 
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