PPCSymbolDB: Add a mutex to prevent m_functions from being accessed by two different threads on boot.

On boot should be the only time this happens.

Source/Core/Core/Boot/Boot.h

@@ -159,7 +159,6 @@ public:
   static bool BootUp(Core::System& system, const Core::CPUThreadGuard& guard,
                      std::unique_ptr<BootParameters> boot);
 
-
 private:
   static bool DVDRead(Core::System& system, const DiscIO::VolumeDisc& disc, u64 dvd_offset,
                       u32 output_address, u32 length, const DiscIO::Partition& partition);

Source/Core/Core/PowerPC/PPCSymbolDB.cpp

@@ -6,6 +6,7 @@
 #include <algorithm>
 #include <cstring>
 #include <map>
+#include <mutex>
 #include <ranges>
 #include <sstream>
 #include <string>
@@ -135,6 +136,13 @@ void PPCSymbolDB::DetermineNoteLayers()
 
 Common::Symbol* PPCSymbolDB::GetSymbolFromAddr(u32 addr)
 {
+  // If m_functions is changing, there should be a PPCSymbolsChanged signal afterward. The signal
+  // will re-update persistent symbol displays by calling this function. Only one-off calls to this
+  // function, such as printing the symbol to console, should be affected by leaving early.
+  std::unique_lock<std::mutex> lock(m_write_lock, std::try_to_lock);
+  if (!lock.owns_lock() || m_functions.empty())
+    return nullptr;
+
   auto it = m_functions.lower_bound(addr);
 
   if (it != m_functions.end())
@@ -156,7 +164,8 @@ Common::Symbol* PPCSymbolDB::GetSymbolFromAddr(u32 addr)
 
 Common::Note* PPCSymbolDB::GetNoteFromAddr(u32 addr)
 {
-  if (m_notes.empty())
+  std::unique_lock<std::mutex> lock(m_write_lock, std::try_to_lock);
+  if (!lock.owns_lock() || m_notes.empty())
     return nullptr;
 
   auto itn = m_notes.lower_bound(addr);
@@ -203,6 +212,10 @@ std::string_view PPCSymbolDB::GetDescription(u32 addr)
 
 void PPCSymbolDB::FillInCallers()
 {
+  std::unique_lock<std::mutex> lock(m_write_lock, std::try_to_lock);
+  if (!lock.owns_lock())
+    return;
+
   for (auto& p : m_functions)
   {
     p.second.callers.clear();
@@ -303,6 +316,10 @@ bool PPCSymbolDB::FindMapFile(std::string* existing_map_file, std::string* writa
 
 bool PPCSymbolDB::LoadMapOnBoot(const Core::CPUThreadGuard& guard)
 {
+  // Loads from emuthread and can crash with main thread accessing the map. Any other loads will be
+  // done on the main thread and should be safe. Returns true if m_functions was changed.
+  std::lock_guard lock(m_write_lock);
+
   std::string existing_map_file;
   if (!PPCSymbolDB::FindMapFile(&existing_map_file, nullptr))
     return Clear();

Source/Core/Core/PowerPC/PPCSymbolDB.h

@@ -3,6 +3,7 @@
 
 #pragma once
 
+#include <mutex>
 #include <string>
 #include <string_view>
 
@@ -48,4 +49,7 @@ public:
   void LogFunctionCall(u32 addr);
 
   static bool FindMapFile(std::string* existing_map_file, std::string* writable_map_file);
+
+private:
+  std::mutex m_write_lock;
 };