feat: port gcc to MontaukOS

kernel/src/Sched/Scheduler.hpp

@@ -19,9 +19,14 @@ namespace Sched {
     static constexpr int MaxProcesses = 256;
     static constexpr uint64_t StackPages = 4;  // 16 KiB kernel stack per thread
     static constexpr uint64_t StackSize = StackPages * 0x1000;
-    static constexpr uint64_t UserStackPages = 8;  // 32 KiB user stack (main thread)
+    static constexpr uint64_t UserStackPages = 8;  // 32 KiB user stack (main thread, eagerly mapped)
     static constexpr uint64_t UserStackSize = UserStackPages * 0x1000;
     static constexpr uint64_t UserStackTop = 0x7FFFFFF000ULL;  // Main-thread user stack top VA
+    // The main-thread stack demand-grows below the eager region up to this
+    // limit: page faults in [UserStackTop - UserStackMax, UserStackTop -
+    // UserStackSize) map fresh zeroed pages instead of killing the process.
+    // Heavy recursive programs (GCC's cc1plus) need megabytes of stack.
+    static constexpr uint64_t UserStackMax = 64 * 1024 * 1024;  // 64 MiB
     static constexpr uint64_t UserHeapBase = 0x40000000ULL;    // User heap start VA
     static constexpr uint32_t UserReadDirSlots = 64;           // rotating scratch pages for SYS_READDIR
     static constexpr uint64_t UserReadDirBase =
@@ -139,6 +144,12 @@ namespace Sched {
     // Get a pointer to the currently running thread's slot (may be a sibling).
     Process* GetCurrentThreadPtr();
 
+    // Demand-grow the current process's main-thread user stack. Called from
+    // the page fault handler when a non-present fault lands in the stack
+    // growth region. Maps one zeroed page at the faulting address and returns
+    // true if the faulting instruction should be retried.
+    bool TryGrowUserStack(uint64_t faultAddr);
+
     // Called by terminated processes to mark themselves done.
     // Tears down the entire process (kills all sibling threads, frees address space).
     void ExitProcess();