From 2026a4f95f3a7dcc9613c8abe2d79d8284b8cd37 Mon Sep 17 00:00:00 2001
From: Anton Kling <anton@kling.gg>
Date: Wed, 8 Nov 2023 18:10:56 +0100
Subject: Kernel/MMU: Detect system memory and dynamically adjust memory usage
 available

Previously this would be hardcoded but now it can be detected by the
bootloader and passed in via the multiboot header.
---
 kernel/includes/mmu.h |  5 +++--
 kernel/init/kernel.c  | 12 ++++++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/kernel/includes/mmu.h b/kernel/includes/mmu.h
index 1df337d..f3af5e4 100644
--- a/kernel/includes/mmu.h
+++ b/kernel/includes/mmu.h
@@ -31,7 +31,8 @@ typedef struct PageDirectory {
   uint32_t physical_address;
 } PageDirectory;
 
-int mmu_allocate_region(void *ptr, size_t n, mmu_flags flags, PageDirectory *pd);
+int mmu_allocate_region(void *ptr, size_t n, mmu_flags flags,
+                        PageDirectory *pd);
 void mmu_allocate_shared_kernel_region(void *rc, size_t n);
 void *mmu_find_unallocated_virtual_range(void *addr, size_t length);
 void mmu_remove_virtual_physical_address_mapping(void *ptr, size_t length);
@@ -45,7 +46,7 @@ void mmu_map_physical(void *dst, PageDirectory *d, void *physical,
 void mmu_free_pages(void *a, uint32_t n);
 
 void flush_tlb(void);
-void paging_init(void);
+void paging_init(uint64_t memsize);
 PageDirectory *get_active_pagedirectory(void);
 void move_stack(uint32_t new_stack_address, uint32_t size);
 void switch_page_directory(PageDirectory *directory);
diff --git a/kernel/init/kernel.c b/kernel/init/kernel.c
index 8c0f70c..9fe7ac4 100644
--- a/kernel/init/kernel.c
+++ b/kernel/init/kernel.c
@@ -39,17 +39,21 @@ uintptr_t data_end;
 
 void kernel_main(uint32_t kernel_end, unsigned long magic, unsigned long addr,
                  uint32_t inital_stack) {
-  data_end = kernel_end;
+  (void)kernel_end;
+  data_end = 0xc0400000;
   inital_esp = inital_stack;
 
   asm("cli");
   kprintf("If you see this then the serial driver works :D.\n");
   assert(magic == MULTIBOOT_BOOTLOADER_MAGIC);
 
-  paging_init();
+  multiboot_info_t *mb = (multiboot_info_t *)(addr + 0xc0000000);
+  uint32_t mem_kb = mb->mem_lower;
+  uint32_t mem_mb = (mb->mem_upper - 1000) / 1000;
+  uint64_t memsize_kb = mem_mb * 1000 + mem_kb;
+  paging_init(memsize_kb);
   klog("Paging Initalized", LOG_SUCCESS);
-  multiboot_info_t *mb =
-      mmu_map_frames((multiboot_info_t *)addr, sizeof(multiboot_info_t));
+  mb = mmu_map_frames((multiboot_info_t *)addr, sizeof(multiboot_info_t));
 
   gdt_init();
   klog("GDT Initalized", LOG_SUCCESS);
-- 
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