os: rework kernel architecture

Rework the code structure and architecture of the kernel by separating
platform-dependent and platform-independent code more cleanly. As of
this patchset, full feature parity has not been achieved. Nonetheless, a
sufficient subset of functionality has been ported to the new
architecture to demonstrate the feasibility of the new structure.

1 files changed, 60 insertions, 0 deletions

diff --git a/arch/x86_64/src/boot/entry64.s b/arch/x86_64/src/boot/entry64.s
new file mode 100644
index 0000000..657b0a8
--- /dev/null
+++ b/arch/x86_64/src/boot/entry64.s
@@ -0,0 +1,60 @@
+.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
+
+.align 16
+.global stack_top
+stack_bottom: .skip 1 << 20
+stack_top:
+stack_size = stack_top - stack_bottom
+
+.section .boot_text, "ax", @progbits
+.code64
+
+.global _entry64
+_entry64:
+    mov $global_descriptor_table_data, %rax
+    mov %rax, %ss
+    mov %rax, %ds
+    mov %rax, %es
+    mov %rax, %fs
+    mov %rax, %gs
+
+    mov $stack_top, %rsp
+    mov %rsp, %rbp
+
+    mov multiboot_information_pointer, %rax
+    or $TEACHOS_VMA, %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
+    mov %rax, %rbp
+    mov %rax, %rdx
+    mov %rax, %rsi
+
+    mov $stack_size, %rcx
+    shr $3, %rcx
+    lea (stack_bottom), %rdi
+    rep stosq
+
+    mov %rax, %rdi
+
+    call main
+
+1:
+    hlt
+    jmp 1b