Add a symbol pointing to the end of used kernel memory

src/linker.ld

@@ -43,4 +43,8 @@ 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. */
+	.end BLOCK(4K) : ALIGN(4K)
+	{
+		_kernel_end = . ;
+	}
 }

src/mem.c

@@ -46,9 +46,6 @@ void populate_page_table(page_table_entry* table, void* start, int num, int offs
     }
 }
 
-// TODO: put this as a label at the end of the code, so we can take
-// its address
-#define KERN_END 0x204000
 
 page_directory_entry* mem_init_kern_tables(multiboot_memory_map* mmap, multiboot_memory_map* mmap_end)
 {
@@ -56,8 +53,8 @@ page_directory_entry* mem_init_kern_tables(multiboot_memory_map* mmap, multiboot
     // Make a page directory structure easily
     page_directory_entry* kern_page_dir = initiate_directory();
 
-    // This line will change with the above TODO
-    page_table_entry* next_table = (page_table_entry*) KERN_END;
+    // _kern_end is defined in the linker script
+    page_table_entry* next_table = (page_table_entry*) &_kernel_end;
 
     int current_dir_entry = 0;
 

src/mem.h

@@ -27,6 +27,9 @@ typedef uint32_t page_table_entry;
 extern void loadPageDirectory(page_directory_entry*);
 extern void enablePaging();
 
+// Defined in linker.ld
+extern char _kernel_end[];
+
 // Defined in the file mem.c
 page_directory_entry* initiate_directory();
 page_directory_entry* mem_init_kern_tables(multiboot_memory_map* mmap, multiboot_memory_map* mmap_end);
@@ -38,4 +41,30 @@ void* memory_mark;
 
 void* malloc(uint32_t bytes);
 
+// Required for elf loading - virtual memory and stuff
+
 #endif
+
+// TODO:
+/*
+  Two stage memory thing.
+
+  Ensure kernel is paged.
+  Ensure that a space equal to <remaining_memory> / (4096 * 8) is paged. This is for the following struct
+  Create binary array specifying which pages are used (abstract ownership a bit maybe to pid, or just use bit array)
+    Place in allocated space
+
+  Write allocor for pages. This should be the only way to get ownership of pages.
+    - takes a page directory and a new address as an argument.
+    - Sholud be called by the other malloc function, or by construction of page tables
+    - flips a bit in a binary array
+
+    - Also write corresponding free, flip bit and remove entry in page dir/table
+
+  Write more versatile malloc/free
+    - Use struct{void* next, size_t size} before every hunk. Walk list to find total size, use this to determine if more pages are needed. Or something
+
+
+    Problems - how to determine when new pages are needed
+             - how to load in elf stuff at arbitrary locations
+*/