feat: port gcc to MontaukOS

kernel/src/Sched/Scheduler.cpp

@@ -1103,6 +1103,48 @@ namespace Sched {
         return &processTable[slot];
     }
 
+    // Serializes stack growth so two threads faulting on the same page do not
+    // both map it (the loser's page would leak: FreeUserHalf only frees pages
+    // still referenced by the page tables).
+    static kcp::Spinlock stackGrowLock;
+
+    bool TryGrowUserStack(uint64_t faultAddr) {
+        constexpr uint64_t growBase = UserStackTop - UserStackMax;
+        constexpr uint64_t eagerBase = UserStackTop - UserStackSize;
+        if (faultAddr < growBase || faultAddr >= eagerBase) return false;
+
+        Process* proc = GetCurrentProcessPtr();
+        if (proc == nullptr) return false;
+
+        uint64_t pageVa = faultAddr & ~0xFFFULL;
+
+        stackGrowLock.Acquire();
+
+        // Another thread may have mapped this page between the fault and here.
+        if (Memory::VMM::Paging::IsUserRangeAccessible(proc->pml4Phys, pageVa, 0x1000, true)) {
+            stackGrowLock.Release();
+            return true;
+        }
+
+        void* page = Memory::g_pfa->AllocateZeroed();
+        if (page == nullptr) {
+            stackGrowLock.Release();
+            Kt::KernelLogStream(Kt::ERROR, "Sched")
+                << "Out of memory growing user stack for pid " << proc->pid;
+            return false;
+        }
+        uint64_t physAddr = Memory::SubHHDM((uint64_t)page);
+        if (!Memory::VMM::Paging::MapUserIn(proc->pml4Phys, physAddr, pageVa)) {
+            stackGrowLock.Release();
+            Memory::g_pfa->Free(page);
+            return false;
+        }
+        stackGrowLock.Release();
+
+        asm volatile("invlpg (%0)" :: "r"(pageVa) : "memory");
+        return true;
+    }
+
     void ExitProcess() {
         auto* cpu = Smp::GetCurrentCpuData();
         int slot = cpu->currentSlot;