kernel: mm: Detect memory regions.

Doesn't do much, but lays down the foundation for future memory management
efforts.

1 files changed, 78 insertions, 0 deletions

diff --git a/kernel/mm/memory_map.c b/kernel/mm/memory_map.c
new file mode 100644
index 0000000..c6aefee
--- /dev/null
+++ b/kernel/mm/memory_map.c
@@ -0,0 +1,78 @@
+/*
+ * CMOS
+ * Copyright (C) 2025 Raghuram Subramani <raghus2247@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+
+#include <common.h>
+
+#include <kernel/halt.h>
+#include <libk/stdio.h>
+
+#include <mm/multiboot.h>
+
+ALWAYS_INLINE static char *
+memory_map_fetch_type(multiboot_memory_map_t *mmap)
+{
+  switch (mmap->type) {
+  case MULTIBOOT_MEMORY_AVAILABLE:
+    return "AVAILABLE";
+  case MULTIBOOT_MEMORY_RESERVED:
+    return "RESERVED";
+  case MULTIBOOT_MEMORY_ACPI_RECLAIMABLE:
+    return "ACPI_RECLAIMABLE";
+  case MULTIBOOT_MEMORY_NVS:
+    return "NVS";
+  case MULTIBOOT_MEMORY_BADRAM:
+    return "BADRAM";
+  default:
+    return "UNKNOWN";
+  }
+}
+
+void
+memory_map_load(multiboot_info_t *multiboot_info)
+{
+  printk("mm", "Loading Memory Map:");
+
+  /* https://www.gnu.org/software/grub/manual/multiboot/multiboot.html:
+   *
+   * If bit 6 in the ‘flags’ word is set, then the ‘mmap_*’ fields are
+   * valid, and indicate the address and length of a buffer containing a
+   * memory map of the machine provided by the BIOS. ‘mmap_addr’ is the
+   * address, and ‘mmap_length’ is the total size of the buffer. The buffer
+   * consists of one or more of the following size/structure pairs (‘size’
+   * is really used for skipping to the next pair): */
+
+  if (!(multiboot_info->flags & MULTIBOOT_INFO_ELF_SHDR)) {
+    printk("mm", "Invalid memory map!");
+    halt();
+  }
+
+  for (uint32_t i = 0; i < multiboot_info->mmap_length;
+       i += sizeof(multiboot_memory_map_t)) {
+    multiboot_memory_map_t *mmap
+        = (multiboot_memory_map_t *) (multiboot_info->mmap_addr + i);
+
+    printk("mm",
+           "start: 0x%x | length: 0x%x | size: 0x%x | type: %s",
+           mmap->addr_low,
+           mmap->len_low,
+           mmap->size,
+           memory_map_fetch_type(mmap));
+  }
+}