Add a bootstrap physical memory manager.

This will allow the real physical memory manager to use allocations.

zion/memory/physical_memory.cpp

@@ -0,0 +1,53 @@
+#include "memory/physical_memory.h"
+
+#include "boot/boot_info.h"
+#include "debug/debug.h"
+
+namespace phys_mem {
+namespace {
+
+struct BootstrapMemory {
+  uint64_t init_page = 0;
+  uint64_t next_page = 0;
+  uint64_t max_page = 0;
+};
+
+static BootstrapMemory gBootstrap;
+static bool gBootstrapEnabled = false;
+
+};  // namespace
+
+void InitBootstrapPageAllocation() {
+  const limine_memmap_response& memmap = boot::GetMemoryMap();
+  for (uint64_t i = 0; i < memmap.entry_count; i++) {
+    const limine_memmap_entry& entry = *memmap.entries[i];
+    // We may want to chose a high address space to not limit
+    // the number of buffers we can allocate later but
+    // if we limit the number of pages this should be fine.
+    // Currently set to the minimum of 3 for one kernel heap allocation:
+    // PageDirectory + PageTable + Page
+    if (entry.type == 0 && entry.length >= 0x3000) {
+      gBootstrap.init_page = entry.base;
+      gBootstrap.next_page = entry.base;
+      gBootstrap.max_page = entry.base + 0x3000;
+      gBootstrapEnabled = true;
+      return;
+    }
+  }
+}
+
+uint64_t AllocatePage() {
+  if (!gBootstrapEnabled) {
+    panic("No Bootstrap Memory Manager");
+  }
+
+  uint64_t page = gBootstrap.next_page;
+  if (page == gBootstrap.max_page) {
+    panic("Bootstrap Memory Manager OOM");
+  }
+  gBootstrap.next_page += 0x1000;
+
+  return page;
+}
+
+}  // namespace phys_mem