x86_64/vga: rely less on magic state

3 files changed, 50 insertions, 23 deletions

diff --git a/arch/x86_64/src/boot/entry64.s b/arch/x86_64/src/boot/entry64.s
index c5df5db..636e4cd 100644
--- a/arch/x86_64/src/boot/entry64.s
+++ b/arch/x86_64/src/boot/entry64.s
@@ -1,3 +1,16 @@
+.section .bss, "aw", @nobits
+
+//! A structure containing information gathered during the bootstrap process.
+//! Expected layout (as described by teachos::boot::information):
+//!
+//! struct
+//! {
+//!   multiboot2::information_view const * mbi;
+//!   std::size_t vga_buffer_index;
+//! }
+.global bootstrap_information
+bootstrap_information: .skip 16
+
 .section .boot_text, "ax", @progbits
 .code64
 
@@ -10,6 +23,12 @@ _entry64:
     mov %rax, %fs
     mov %rax, %gs
 
+    mov multiboot_information_pointer, %rax
+    mov vga_buffer_pointer, %rdx
+    sub $0xb8000, %rdx
+    mov %rax, (bootstrap_information)
+    mov %rdx, (bootstrap_information + 8)
+
     call invoke_global_constructors
     
     xor %rax, %rax
diff --git a/arch/x86_64/src/kapi/memory.cpp b/arch/x86_64/src/kapi/memory.cpp
index 5142a2a..3848fb8 100644
--- a/arch/x86_64/src/kapi/memory.cpp
+++ b/arch/x86_64/src/kapi/memory.cpp
@@ -24,7 +24,7 @@ namespace teachos::memory
 
     auto create_memory_information() -> x86_64::region_allocator::memory_information
     {
-      auto const & mbi = boot::x86_64::multiboot_information_pointer.get();
+      auto const & mbi = boot::bootstrap_information.mbi;
 
       return {.image_range = std::make_pair(physical_address{&boot::x86_64::_start_physical},
                                             physical_address{&boot::x86_64::_end_physical}),
@@ -35,7 +35,7 @@ namespace teachos::memory
 
     auto create_early_frame_allocator()
     {
-      auto memory_map = boot::x86_64::multiboot_information_pointer->maybe_memory_map();
+      auto memory_map = boot::bootstrap_information.mbi->maybe_memory_map();
       if (!memory_map)
       {
         system::panic("[x86_64] Failed to create early allocator, no memory map available.");
diff --git a/arch/x86_64/src/vga/text.cpp b/arch/x86_64/src/vga/text.cpp
index 6ecffa3..8b7f01b 100644
--- a/arch/x86_64/src/vga/text.cpp
+++ b/arch/x86_64/src/vga/text.cpp
@@ -1,38 +1,41 @@
 #include "x86_64/vga/text.hpp"
 
+#include "kapi/boot.hpp"
+
 #include "x86_64/boot/boot.hpp"
+#include "x86_64/boot/ld.hpp"
 #include "x86_64/vga/crtc.hpp"
 
 #include <algorithm>
 #include <bit>
 #include <cstddef>
+#include <cstdint>
 #include <string_view>
 #include <utility>
 
 namespace teachos::vga::x86_64::text
 {
-  using boot::x86_64::vga_buffer_pointer;
-
   namespace
   {
-    // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
-    auto constinit buffer_offset = std::ptrdiff_t{};
-
+    constexpr auto BUFFER_BASE_ADDRESS = std::uintptr_t{0xb8000};
     constexpr auto DEFAULT_TEXT_BUFFER_WIDTH = 80U;
     constexpr auto DEFAULT_TEXT_BUFFER_HEIGHT = 25U;
     constexpr auto CURSOR_ENABLED_BIT = 5U;
-
-    auto write_char(char code_point, attribute attribute) -> void
-    {
-      vga_buffer_pointer[buffer_offset++] = std::pair{code_point, std::bit_cast<std::byte>(attribute)};
-    };
   }  // namespace
 
+  std::span<device::glyph> const device::buffer =
+      std::span{std::bit_cast<device::glyph *>(BUFFER_BASE_ADDRESS +
+                                               std::bit_cast<std::uintptr_t>(&teachos::boot::x86_64::TEACHOS_VMA)),
+                DEFAULT_TEXT_BUFFER_WIDTH * DEFAULT_TEXT_BUFFER_HEIGHT};
+
+  device::device()
+      : m_position{boot::bootstrap_information.vga_buffer_index}
+  {}
+
   auto device::clear(attribute attribute) -> void
   {
-    buffer_offset = 0;
-    std::ranges::fill_n(vga_buffer_pointer.get(), DEFAULT_TEXT_BUFFER_WIDTH * DEFAULT_TEXT_BUFFER_HEIGHT,
-                        std::pair{' ', std::bit_cast<std::byte>(attribute)});
+    m_position = 0;
+    std::ranges::fill(buffer, std::pair{' ', std::bit_cast<std::byte>(attribute)});
   }
 
   auto device::cursor(bool enabled) -> void
@@ -45,30 +48,35 @@ namespace teachos::vga::x86_64::text
 
   auto device::newline() -> void
   {
-    auto current_line = buffer_offset / DEFAULT_TEXT_BUFFER_WIDTH;
+    auto current_line = m_position / DEFAULT_TEXT_BUFFER_WIDTH;
     auto next_line = current_line + 1;
 
     if (std::cmp_greater_equal(next_line, DEFAULT_TEXT_BUFFER_HEIGHT))
     {
-      auto begin = vga_buffer_pointer + DEFAULT_TEXT_BUFFER_WIDTH;
-      auto end = vga_buffer_pointer + DEFAULT_TEXT_BUFFER_WIDTH * DEFAULT_TEXT_BUFFER_HEIGHT;
-      std::ranges::move(begin, end, vga_buffer_pointer.get());
-      buffer_offset = current_line * DEFAULT_TEXT_BUFFER_WIDTH;
+      auto begin = buffer.begin() + DEFAULT_TEXT_BUFFER_WIDTH;
+      auto end = buffer.begin() + DEFAULT_TEXT_BUFFER_WIDTH * DEFAULT_TEXT_BUFFER_HEIGHT;
+      std::ranges::move(begin, end, buffer.begin());
+      m_position = current_line * DEFAULT_TEXT_BUFFER_WIDTH;
     }
     else
     {
-      buffer_offset = next_line * DEFAULT_TEXT_BUFFER_WIDTH;
+      m_position = next_line * DEFAULT_TEXT_BUFFER_WIDTH;
     }
   }
 
   auto device::write(std::string_view code_points, attribute attribute) -> void
   {
-    std::ranges::for_each(code_points, [&](auto code_point) -> void { write_char(code_point, attribute); });
+    std::ranges::for_each(code_points, [&](auto code_point) -> void { write(code_point, attribute); });
   }
 
+  auto device::write(char code_point, attribute attribute) -> void
+  {
+    buffer[m_position++] = std::pair{code_point, std::bit_cast<std::byte>(attribute)};
+  };
+
   auto device::writeln(std::string_view code_points, attribute attribute) -> void
   {
-    std::ranges::for_each(code_points, [&](auto code_point) -> void { write_char(code_point, attribute); });
+    std::ranges::for_each(code_points, [&](auto code_point) -> void { write(code_point, attribute); });
     newline();
   }