1 files changed, 103 insertions, 0 deletions
diff --git a/Kernel/HALKit/AMD64/HalPageAlloc.cpp b/Kernel/HALKit/AMD64/HalPageAlloc.cpp
new file mode 100644
index 00000000..db2aad73
--- /dev/null
+++ b/Kernel/HALKit/AMD64/HalPageAlloc.cpp
@@ -0,0 +1,103 @@
+/* -------------------------------------------
+
+    Copyright SoftwareLabs
+
+------------------------------------------- */
+
+#include <ArchKit/ArchKit.hpp>
+#include <HALKit/AMD64/HalPageAlloc.hpp>
+#include <NewKit/Defines.hpp>
+#include <NewKit/KernelCheck.hpp>
+
+STATIC NewOS::Boolean kAllocationInProgress = false;
+
+namespace NewOS
+{
+	namespace HAL
+	{
+		namespace Detail
+		{
+			struct VirtualMemoryHeader
+			{
+				UInt32	Magic;
+				Boolean Present;
+				Boolean ReadWrite;
+				Boolean User;
+				SizeT	PageSize;
+			};
+
+			struct VirtualMemoryHeaderTraits
+			{
+				/// @brief Get next header.
+				/// @param current
+				/// @return
+				VirtualMemoryHeader* Next(VirtualMemoryHeader* current)
+				{
+					return current + sizeof(PTE) + current->PageSize;
+				}
+
+				/// @brief Get previous header.
+				/// @param current
+				/// @return
+				VirtualMemoryHeader* Prev(VirtualMemoryHeader* current)
+				{
+					return current - sizeof(PTE) - current->PageSize;
+				}
+			};
+		} // namespace Detail
+
+		/// @brief Allocates a new page of memory.
+		/// @param sz the size of it.
+		/// @param rw read/write flag.
+		/// @param user user flag.
+		/// @return the page table of it.
+		STATIC auto hal_try_alloc_new_page(Boolean rw, Boolean user, SizeT size) -> VoidPtr
+		{
+			if (kAllocationInProgress)
+				return nullptr;
+
+			kAllocationInProgress = true;
+
+			constexpr auto cVMTMagic = 0xDEEFD00D;
+
+			///! fetch from the start.
+			Detail::VirtualMemoryHeader*	  vmHeader = reinterpret_cast<Detail::VirtualMemoryHeader*>(kKernelVirtualStart);
+			Detail::VirtualMemoryHeaderTraits traits;
+
+			while (vmHeader->Present &&
+				   vmHeader->Magic != cVMTMagic)
+			{
+				vmHeader = traits.Next(vmHeader);
+			}
+
+			vmHeader->Magic		= cVMTMagic;
+			vmHeader->Present	= true;
+			vmHeader->ReadWrite = rw;
+			vmHeader->User		= user;
+			vmHeader->PageSize	= size;
+
+			kAllocationInProgress = false;
+
+			return reinterpret_cast<VoidPtr>(vmHeader);
+		}
+
+		/// @brief Allocate a new page to be used by the OS.
+		/// @param rw read/write bit.
+		/// @param user user bit.
+		/// @return
+		auto hal_alloc_page(Boolean rw, Boolean user, SizeT size) -> VoidPtr
+		{
+			/// Wait for a ongoing allocation to complete.
+			while (kAllocationInProgress)
+			{
+				;
+			}
+
+			if (size == 0)
+				++size;
+
+			/// allocate new page.
+			return hal_try_alloc_new_page(rw, user, size);
+		}
+	} // namespace HAL
+} // namespace NewOS