vmm: map multiboot structs

5 files changed, 99 insertions, 14 deletions

diff --git a/src/boot.S b/src/boot.S
index 6588004..d1c4f9b 100644
--- a/src/boot.S
+++ b/src/boot.S
@@ -38,9 +38,11 @@ stack_top:
 
 .section .pages, "aw", @nobits
 .align 4096
-boot_page_directory:
+.global kernel_pagedir
+kernel_pagedir:
     .skip 1024 * 4
-boot_page_table1:
+.global kernel_ptable0
+kernel_ptable0:
     .skip 1024 * 4
 
 
@@ -55,8 +57,8 @@ boot_page_table1:
 _start:
     cli
 
-    # Physical address of boot_page_table1.
-    movl $(boot_page_table1 - VADDR_OFFSET), %edi
+    # Physical address of kernel_ptable0.
+    movl $(kernel_ptable0 - VADDR_OFFSET), %edi
 
     # Only map the kernel.
     mov $_kernel_start - VADDR_OFFSET, %esi
@@ -75,14 +77,14 @@ l_page_init:
 
 	# Size of page is 4096 bytes.
 	addl $4096, %esi
-	# Size of entries in boot_page_table1 is 4 bytes.
+	# Size of entries in kernel_ptable0 is 4 bytes.
 	addl $4, %edi
 	# Loop to the next entry if we haven't finished.
 	loop l_page_init
 
 map_vga:
     # Map VGA video memory to 0xC03FF000 as "present, writable".
-    movl $(0x000B8000 | 0x003), boot_page_table1 - VADDR_OFFSET + 1023 * 4
+    movl $(0x000B8000 | 0x003), kernel_ptable0 - VADDR_OFFSET + 1023 * 4
 
 /*
     Enabling paging does not change the next instruction, which continues to be physical. Therefore, map the kernel
@@ -91,11 +93,11 @@ map_vga:
       - entry   1       starts 0x0040 0000      ends 0x007f ffff
       - entry 768       starts 0xc000 0000      ends 0xc03f ffff
  */
-    movl $(boot_page_table1 - VADDR_OFFSET + 0x003), boot_page_directory - VADDR_OFFSET + 1 * 4
-    movl $(boot_page_table1 - VADDR_OFFSET + 0x003), boot_page_directory - VADDR_OFFSET + 768 * 4
+    movl $(kernel_ptable0 - VADDR_OFFSET + 0x003), kernel_pagedir - VADDR_OFFSET + 1 * 4
+    movl $(kernel_ptable0 - VADDR_OFFSET + 0x003), kernel_pagedir - VADDR_OFFSET + 768 * 4
 
-    # Set cr3 to the address of the boot_page_directory.
-    movl $(boot_page_directory - VADDR_OFFSET), %ecx
+    # Set cr3 to the address of the kernel_pagedir.
+    movl $(kernel_pagedir - VADDR_OFFSET), %ecx
     movl %ecx, %cr3
 
     # Enable paging and the write-protect bit.
@@ -113,7 +115,7 @@ map_vga:
 kinit:
     # At this point, paging is fully set up and enabled.
     # Unmap the identity mapping as it is now unnecessary.
-    movl $0, boot_page_directory + 1 * 4
+    movl $0, kernel_pagedir + 1 * 4
     # Reload crc3 to force a TLB flush so the changes to take effect.
     movl %cr3, %ecx
     movl %ecx, %cr3
diff --git a/src/kernel.cc b/src/kernel.cc
index b7aae2f..0915365 100644
--- a/src/kernel.cc
+++ b/src/kernel.cc
@@ -37,8 +37,15 @@ void kernel_main([[maybe_unused]] uint32_t mb_magic, [[maybe_unused]] uint32_t m
   printk("Hello, kernel World!\n");
 
   dump_address();
-  dump_multiboot(mb_magic, mb_addr);
   // dump_gdt();
+  //
+
+  vmm kvmm;
+  mb_addr = kvmm.map(mb_addr, 0xc03fe000);
+
+  dump_multiboot(mb_magic, mb_addr);
+  //
+  //
 
   GDT gdt;
   IDT idt{gdt.descriptor(GDT::kcode)};
diff --git a/src/kernel/dump_multiboot.cc b/src/kernel/dump_multiboot.cc
index 35c2874..f190cd3 100644
--- a/src/kernel/dump_multiboot.cc
+++ b/src/kernel/dump_multiboot.cc
@@ -5,8 +5,6 @@ extern "C" void dump_multiboot(uint32_t mb_magic, uint32_t mb_addr) {
   printk("multiboot magic: ", uhex{mb_magic}, mb_magic == MULTIBOOT2_BOOTLOADER_MAGIC ? " valid" : " invalid", '\n');
   printk("multiboot  addr: ", uhex{mb_addr}, !(mb_addr & 7) ? " is aligned" : " is not aligned", '\n');
 
-  return;
-
   struct multiboot_tag* tag;
   const uint32_t size = *reinterpret_cast<uint32_t*>(mb_addr);
   printk("Announced mbi size ", size, '\n');
diff --git a/src/vmm.cc b/src/vmm.cc
index 346e6ab..483f02f 100644
--- a/src/vmm.cc
+++ b/src/vmm.cc
@@ -1,3 +1,4 @@
+#include "vmm.h"
 #include <stdlib.h>
 
 typedef void (*constructor)();
@@ -47,3 +48,52 @@ void dump_address() {
          " end: ", uhex{reinterpret_cast<uint32_t>(&end_bss)}, '\n');
 }
 }  // extern "C"
+
+/* boot.S page directory and kernel page table */
+extern uint32_t kernel_pagedir;
+extern uint32_t kernel_ptable0;
+
+constexpr uint32_t to_vma(uint32_t page_dir_address) {
+  page_dir_address &= 0xfffff000;
+  page_dir_address += 0xc0000000;
+  page_dir_address -= 0x00400000;
+  return page_dir_address;
+}
+
+vmm::vmm(uint32_t* addr) : directory{(addr == nullptr) ? &kernel_pagedir : addr} {
+  printk("page directory is at ", uhex{reinterpret_cast<uint32_t>(directory)}, '\n');
+  printk("page table 768       ", uhex{reinterpret_cast<uint32_t>(directory[768])}, '\n');
+  printk("page table 768 vma   ", uhex{to_vma(reinterpret_cast<uint32_t>(directory[768]))}, '\n');
+  printk("kernel_ptable0 is at ", uhex{reinterpret_cast<uint32_t>(&kernel_ptable0)}, '\n');
+
+  uint32_t* page = reinterpret_cast<uint32_t*>(&kernel_ptable0);
+  for (size_t i = 0; i < 32; ++i) {
+    printk(uhex{page[i] & 0xfffff000}, ' ');
+    if (i % 4 == 3) printk('\n');
+  }
+}
+
+uint32_t vmm::map(uint32_t phys_addr, uint32_t dest) {
+  const auto phys_offset = phys_addr % 4096;
+  const auto phys_page = phys_addr - phys_offset;
+
+  const auto table = table_id(dest);
+  const auto page = page_id(dest - table * 4 * 1024 * 1024);
+
+  printk("phys_addr page: ", uhex{phys_page}, '\n');
+  printk("        offset: ", uhex{phys_offset}, '\n');
+  printk("         table: ", table, '\n');
+  printk("          page: ", page, '\n');
+
+  if (directory[table] == 0) return 0;
+
+  uint32_t* page_table = reinterpret_cast<uint32_t*>(to_vma(reinterpret_cast<uint32_t>(directory[table])));
+  if (page_table[page] != 0) return 0;
+  page_table[page] = phys_page | 0x003;
+
+  uint32_t cr0;
+  asm volatile("mov %%cr0, %0" : "=r"(cr0));
+  asm volatile("mov %0, %%cr0" : : "r"(cr0));
+
+  return table * 4 * 1024 * 1024 + page * 4 * 1024 + phys_offset;
+}
diff --git a/src/vmm.h b/src/vmm.h
index 45aa1e8..9de487b 100644
--- a/src/vmm.h
+++ b/src/vmm.h
@@ -1,3 +1,31 @@
+#include <stdlib.h>
+
 #pragma once
 
 extern "C" void dump_address();
+
+struct page_table {
+  uint32_t* addr;
+};
+
+class vmm {
+public:
+  vmm(uint32_t* addr = nullptr);
+
+  constexpr static size_t table_id(uint32_t offset) {
+    offset &= 0xfff00000;
+    offset /= (4 * 1024 * 1024);
+    return static_cast<size_t>(offset);
+  }
+  constexpr static size_t page_id(uint32_t offset) { return static_cast<size_t>(offset / 4096); }
+
+  uint32_t map(uint32_t phys_addr, uint32_t offset);
+
+private:
+  uint32_t* directory;
+};
+
+static_assert(vmm::table_id(0x00001234) == 0);
+static_assert(vmm::table_id(0x00400000) == 1);
+static_assert(vmm::table_id(0xc0000000) == 768);
+static_assert(vmm::table_id(0xc03ff000) == 768);