adds some beginning documentation for setting up paging

kernel/arch/paging/paging.c

@@ -1,8 +0,0 @@
-#include <stdint.h>
-
-#include <stdio.h>
-
-#include <kernel/paging.h>
-
-//extern uint32_t endkernel; // found in link.ld
-

kernel/arch/paging/paging.h

@@ -0,0 +1,86 @@
+/**
+ * The page direcotry and the page table have very specific
+ * entry formats.
+ *
+ * They will be defined here, and constants will be properly allocated.
+ */
+
+/**
+ * Page directory
+ * containes 1024 4 byte entries, making them 4KiB each.
+ *
+ * In the page directory, each entry points to a page table.
+ *
+ *
+ * Page Directory Entry
+ *
+ * (this is following the page size of 0, or 4KiB)
+ * bits:
+ * 31 - 12	: Bits 31-12 of address
+ * 11 - 8 	: AVL
+ * 7 		: PS
+ * 6		: AVL
+ * 5		: A
+ * 4		: PCD
+ * 3 		: PWT
+ * 2 		: U/S
+ * 1		: R/W
+ * 0		: P
+ *
+ *
+ * The address field represnets the physical address of the page table that manages the four megabytes at that point.
+ * It is very important that this address by 4KiB aligned. As the remainder of bytes are overwritten by access bits and such.
+ *
+ * P: Present
+ * 	If the bit is set, the page is actually in physical memory at the moment. For example, when a page is swapped out, it is not in physical memory and therefor not 'Present'.
+ * 	If a page is called, but not present, a page fault will occur, and the OS should handle it.
+ * R/W: Read/Write
+ * 	If the big is set, the page is read/write. Otherwise, it is read-only. The WP bit in CR0 determines if this is only applied to userland, always giving the kernel write access (the default)
+ * 	or both userland and the kernel. (see Intel Manuals 3A 2-20)
+ * U/S: User/Supervisor
+ * 	Controls access to the page based on privelege level. If the bit is set, then the page may be accessed by all; if the bit is not set, however,
+ * 	only the supervisor can access it. For ap age directory entry, the user bit controls access to all the pages referenced by the page directory entry.
+ * 	Therefore if you wish to make a page a user page, you must set the bit in the releveant page directory, as well as the page table entry.
+ * PWT: Write-through
+ * 	Controls Write-through abilities of the page. If the bit is set, write-through caching is enabled.
+ * 	If not, then write-back is enabled instead.
+ * PCD: Cache Disable
+ * 	Cache disable bit, if the bit is set, the page will not be cached. Otherwise, it will be.
+ * A: Accessed
+ * 	Accessed is used to discover whether a PDE or PTE was read during virtual address translation. If it has, then the bit is set, otherwise it is not.
+ * 	Note that, this bit will not be cleared by the CPU, so that burden falls on the OS (if its needed at all).
+ * D: Dirty
+ * 	Dirty is used to determine wether a page has been written to.
+ * PS: Page Size (always 0, since we're using 4KiB pages)
+ * 	Stores the page size for that specific entry. If the bit is set, then the PDE maps a page that is 4MiB in size. Otherwise, it maps to a 4KiB page table.
+ * AVL: Available
+ * 	These bits are unused and are free for the OS to use for accounting information.
+ */
+
+/**
+ * Page Table
+ *
+ * In each page table, as it is, there are also 1024 entries. Each entry points to a 4KiB physical page frame.
+ *
+ * These are called page table entries, and are very similar to the entries described above.
+ *
+ * The first item is a 4KiB aligned physical address. However, these point to a 4KiB block of physical memory, which si then mapped to that location in the page table and driectory.
+ *
+ * 31 - 12	: Bits 31-12 of address
+ * 11 - 9 	: AVL
+ * 8 		: G 
+ * 7		: PAT
+ * 6		: D 
+ * 5		: A
+ * 4 		: PCD
+ * 3 		: PWT
+ * 2		: U/S
+ * 1		: R/W
+ * 0		: P
+ *
+ * G: Global
+ * 	Tells the processor not to invalidate the TLB entry corresponding to the page upon a MOV to CR3 instruction.
+ * 	Bit 7 (PGE) in CR4 must be set to enable global pages.
+ * PAT: Page Attribute Table
+ * 	If PAT is supported, then PAT along with PCD and PWT shall indicate the memory caching type. Otherwise, it is reserved and must be set to 0.
+ */

kernel/arch/paging/paging_src.s

@@ -1,20 +0,0 @@
-global load_page_directory
-load_page_directory:
-	push ebp
-	mov esp, ebp
-	mov eax, [esp + 4]
-	mov cr3, eax
-	mov esp, ebp
-	pop ebp
-	ret
-
-global enable_paging
-enable_paging:
-	push ebp
-	mov ebp, esp
-	mov eax, cr0
-	or eax, 0x80000000
-	mov cr0, eax
-	mov esp, ebp
-	pop ebp
-	ret