kernel: mm: Introduce a WIP physical_mm

5 files changed, 71 insertions, 8 deletions

diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index 733d3c0..73eea0c 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -12,6 +12,7 @@ set(SRC
   kernel/io/io.c
 
   mm/memory_map.c
+  mm/physical_mm/physical_mm.c
 
   drivers/vga_text_buffer/vga_text_buffer.c
   drivers/serial/serial.c
diff --git a/kernel/boot/linker.ld b/kernel/boot/linker.ld
index c90ef51..d98714f 100644
--- a/kernel/boot/linker.ld
+++ b/kernel/boot/linker.ld
@@ -36,6 +36,7 @@ SECTIONS
 	work around this issue. This does not use that feature, so 2M was
 	chosen as a safer option than the traditional 1M. */
   . = 2M;
+  kernel_start = .;
 
   /* First put the multiboot header, as it is required to be put very early
 	in the image or the bootloader won't recognize the file format.
@@ -68,3 +69,5 @@ SECTIONS
   /* The compiler may produce other sections, by default it will put them in
 	a segment with the same name. Simply add stuff here as needed. */
 }
+
+kernel_end = .;
diff --git a/kernel/include/mm/physical_mm.h b/kernel/include/mm/physical_mm.h
new file mode 100644
index 0000000..503a76f
--- /dev/null
+++ b/kernel/include/mm/physical_mm.h
@@ -0,0 +1,37 @@
+/*
+ * 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/>.
+ */
+
+#ifndef __mm_physical_mm_h
+#define __mm_physical_mm_h
+
+#include <common.h>
+
+/*
+ * A byte has 8 bits, hence we can store information for up to 8 blocks at a
+ * time
+ */
+#define BLOCKS_PER_BYTE 8
+
+/* TODO: Update this to 2MiB when PAE is enabled */
+#define BLOCK_SIZE 4 * KiB
+
+#define BLOCK_ALIGN BLOCK_SIZE
+
+void physical_mm_init(void);
+
+#endif
diff --git a/kernel/kernel/kernel.c b/kernel/kernel/kernel.c
index 2e4470b..d1cc6f1 100644
--- a/kernel/kernel/kernel.c
+++ b/kernel/kernel/kernel.c
@@ -20,6 +20,7 @@
 
 #include <mm/memory_map.h>
 #include <mm/multiboot.h>
+#include <mm/physical_mm.h>
 
 #include <kernel/halt.h>
 
@@ -41,15 +42,9 @@ kernel_main(uint32_t magic, multiboot_info_t *multiboot_info)
 
   GDT_load();
   memory_map_load(multiboot_info);
+  physical_mm_init();
 
-  printk("Kernel", "Started.");
-
-  free_memory_regions_t *free_memory_regions = memory_map_get_free_regions();
-  for (int i = 0; i < free_memory_regions->n_regions; i++)
-    printk("Kernel",
-           "start: 0x%.08x | length: 0x%.08x",
-           free_memory_regions->region_list[i]->addr_low,
-           free_memory_regions->region_list[i]->len_low);
+  printk("\nKernel", "Started.");
 
   exit();
   halt(); /* If exit() fails (on real hardware) */
diff --git a/kernel/mm/physical_mm/physical_mm.c b/kernel/mm/physical_mm/physical_mm.c
new file mode 100644
index 0000000..ed7a9ac
--- /dev/null
+++ b/kernel/mm/physical_mm/physical_mm.c
@@ -0,0 +1,27 @@
+/* Bitmap Based Allocation:
+ * https://web.archive.org/web/20190316115948/http://www.brokenthorn.com/Resources/OSDev17.html
+ */
+
+#include <stdint.h>
+
+#include <libk/stdio.h>
+
+#include <mm/memory_map.h>
+#include <mm/physical_mm.h>
+
+extern uint32_t kernel_start;
+extern uint32_t kernel_end;
+
+void
+physical_mm_init(void)
+{
+  free_memory_regions_t *free_memory_regions = memory_map_get_free_regions();
+  for (int i = 0; i < free_memory_regions->n_regions; i++)
+    printk("Kernel",
+           "start: 0x%.08x | length: 0x%.08x",
+           free_memory_regions->region_list[i]->addr_low,
+           free_memory_regions->region_list[i]->len_low);
+
+  printk("physical_mm", "Kernel starts at: 0x%x", &kernel_start);
+  printk("physical_mm", "Kernel ends at: 0x%x", &kernel_end);
+}