Merge branch 'feat_memory_manager' into 'develop_sa'

Finish inital draft of Memory Manager

See merge request teachos/kernel!3

1 files changed, 39 insertions, 41 deletions

diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index 7b4e193..8d27ea1 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -7,38 +7,38 @@
  * Uninitialized data for the bootstrapping process.
  */
 .section .boot_bss, "aw", @nobits
+
+/**
+ * Reserve some space for the Multiboot 2 information pointer.
+ */
+.global multiboot_information_pointer
+multiboot_information_pointer: .skip 4
+
+/**
+ * Align page maps to 4 KiB or the assembler code, will cause crashes when attempting to enable paging.
+ */
 .align 4096
 
 /**
- * Reserve space for the page maps we are going to used during startup.
+ * Reserve space for the page maps we are going to use during startup.
  *
  * Note: We are going to use large pages to make the initial mapping code
  * simpler.
  *
  * We need:
  *   - A single PML 4 (since we will only use 4-level paging)
- *   - 2 PML 3s (since we need to map high (-2GiB) and low (1+MiB) memory)
- *   - 2 PML 2s (since we need to map high (-2GiB) and low (1+MiB) memory)
+ *   - 1 PML 3
+ *   - 1 PML 2
  */
 
 .global page_map_level_4
 page_map_level_4: .skip 512 * 8
 
-.global page_map_level_3_low
-page_map_level_3_low: .skip 512 * 8
-.global page_map_level_3_high
-page_map_level_3_high: .skip 512 * 8
-
-.global page_map_level_2_low
-page_map_level_2_low: .skip 512 * 8
-.global page_map_level_2_high
-page_map_level_2_high: .skip 512 * 8
+.global page_map_level_3
+page_map_level_3: .skip 512 * 8
 
-/**
- * Reserve some space for the Multiboot 2 information pointer.
- */
-.global multiboot_information_pointer
-multiboot_information_pointer: .skip 4
+.global page_map_level_2
+page_map_level_2: .skip 512 * 8
 
 /**
  * Stack space for the bootstrapping process.
@@ -86,6 +86,7 @@ global_descriptor_table_pointer:
  * We are going to print some messages in case we panic during boot, so we are
  * going to store them here as well
  */
+.global message_prefix_panic
 message_prefix_panic:
 .string "TeachOS Panic: "
 message_not_loaded_by_multiboot2:
@@ -113,6 +114,12 @@ vga_buffer_pointer: .long 0xb8000
 .align 16
 .code32
 
+.global halt
+halt:
+1:
+    hlt
+    jmp 1b
+
 /**
  * Print a given panic message and then halt the machine.
  *
@@ -133,7 +140,7 @@ _panic:
     call _print
     add $8, %esp
 
-    hlt
+    call halt
 
 /**
  * Print a message via the VGA buffer.
@@ -193,7 +200,7 @@ _start:
     lgdt (global_descriptor_table_pointer)
     jmp $global_descriptor_table_code,$_transition_to_long_mode
 
-    hlt
+    call halt
 
 /**
  * Assert that the CPU supports going into long mode.
@@ -306,31 +313,23 @@ enable_sse:
  *
  * We map all physical memory we were loaded in plus one additional page. The
  * mapping is done in terms of huge pages (2 MiB per page) to save on required
- * page map entries. Note that we also map memory both in the low and high
- * virtual address ranges, giving us two ways of accessing it. We need to do
- * this, because the bootstrapping code lives in low memory, while the rest of
- * the kernel will reside on the high end.
+ * page map entries.
  */
 prepare_page_maps:
-    /* Add an entry to the PML4, pointing to the low PML3 */
-    mov $page_map_level_3_low, %eax
-    or $0x3, %eax
-    mov %eax, (page_map_level_4 + ((0x0000000000100000 >> 39) & 0x1ff) * 8)
-
-    /* Add an entry to the PML4, pointing to the high PML3 */
-    mov $page_map_level_3_high, %eax
-    or $0x3, %eax
-    mov %eax, (page_map_level_4 + ((0xffffffff80100000 >> 39) & 0x1ff) * 8)
+    /* Map the P4 table recursively */
+    mov $page_map_level_4, %eax
+    or $0b11, %eax /* Write present + writable flags into eax register */
+    mov %eax, (page_map_level_4 + 511 * 8)
 
-    /* Add an entry to the low PML3, pointing to the low PML2 */
-    mov $page_map_level_2_low, %eax
+    /* Add an entry to the PML4, pointing to the PML3 */
+    mov $page_map_level_3, %eax
     or $0x3, %eax
-    mov %eax, (page_map_level_3_low + ((0x0000000000100000 >> 30) & 0x1ff) * 8)
+    mov %eax, (page_map_level_4 + ((0x0000000000100000 >> 39) & 0x1ff) * 8)
 
-    /* Add an entry to the high PML3, pointing to the high PML2 */
-    mov $page_map_level_2_high, %eax
+    /* Add an entry to the PML3, pointing to the PML2 */
+    mov $page_map_level_2, %eax
     or $0x3, %eax
-    mov %eax, (page_map_level_3_high + ((0xffffffff80100000 >> 30) & 0x1ff) * 8)
+    mov %eax, (page_map_level_3 + ((0x0000000000100000 >> 30) & 0x1ff) * 8)
 
     xor %ecx, %ecx
 
@@ -342,8 +341,7 @@ prepare_page_maps:
     mov $(1 << 21), %eax
     mul %ecx
     or $((1 << 0) | (1 << 1) | (1 << 7)), %eax
-    mov %eax, page_map_level_2_low(,%ecx,8)
-    mov %eax, page_map_level_2_high(,%ecx,8)
+    mov %eax, page_map_level_2(,%ecx,8)
 
     inc %ecx
     cmp %esi, %ecx
@@ -367,4 +365,4 @@ _transition_to_long_mode:
     call _init
 
     call kernel_main
-    hlt
+    call halt