A20, E820h, Real Mode Emulation

1 files changed, 33 insertions, 0 deletions

diff --git a/src/loader/ent.asm b/src/loader/ent.asm
new file mode 100644
index 0000000..47cf49b
--- /dev/null
+++ b/src/loader/ent.asm
@@ -0,0 +1,33 @@
+; MIT License, Copyright (c) 2021 Marvin Borner
+
+extern bss_begin
+extern bss_end
+extern start
+extern gdt
+
+section .entry
+
+global _start
+_start:
+	cld
+
+	; Clear bss section
+	xor al, al
+	mov edi, bss_begin
+	mov ecx, bss_end
+	sub ecx, bss_begin
+	rep stosb
+
+	lgdt [gdt]
+	jmp 0x18:.reload_cs
+
+.reload_cs:
+	mov eax, 0x20
+	mov ds, ax
+	mov es, ax
+	mov fs, ax
+	mov gs, ax
+	mov ss, ax
+
+	cli
+	jmp start