From 6e52d3e6ae1d1612884d8d1533007e1d46f0c4eb Mon Sep 17 00:00:00 2001
From: Joursoir <chat@joursoir.net>
Date: Tue, 28 Sep 2021 22:54:29 +0000
Subject: x86/boot: add 32bit startup code

---
 arch/x86/boot/head.s         | 27 +++++++++++++++++++++++++++
 arch/x86/boot/kernel_entry.s | 12 ------------
 2 files changed, 27 insertions(+), 12 deletions(-)
 create mode 100644 arch/x86/boot/head.s
 delete mode 100644 arch/x86/boot/kernel_entry.s

diff --git a/arch/x86/boot/head.s b/arch/x86/boot/head.s
new file mode 100644
index 0000000..a1bc6d1
--- /dev/null
+++ b/arch/x86/boot/head.s
@@ -0,0 +1,27 @@
+/*
+	head.s is loaded at 0x1000 (by second stage), its main goal
+	is run 32-bit startup code.
+
+	After that manipulations it jumps to kernel written by C
+*/
+
+.code32							# Tell GAS to generate 32 bit code
+.extern kernel_main
+
+.set CODESEG, 0x08
+.set DATASEG, 0x10
+
+.global _start
+_start:
+	mov $DATASEG, %ax			# Point segment registers to the
+	mov %ax, %ds				# data selector we defined in our GDT
+	mov %ax, %es
+	mov %ax, %ss
+	mov %ax, %fs
+	mov %ax, %gs
+
+	mov $0x90000, %ebp			# Update stack position so it is right
+	mov %ebp, %esp				# at the top of the free space.
+
+	call kernel_main
+	jmp . 						# infinite loop
diff --git a/arch/x86/boot/kernel_entry.s b/arch/x86/boot/kernel_entry.s
deleted file mode 100644
index e0fd132..0000000
--- a/arch/x86/boot/kernel_entry.s
+++ /dev/null
@@ -1,12 +0,0 @@
-# bootsect.s loads the kernel and transfers control to SYSSEG address.
-# We cannot be sure that the main() function will be exactly at this
-# address.
-
-# Therefore, we will use a small trick for entering the kernel correctly:
-# Locate this small assembly routine at the beginning of the SYSSEG
-# address => we can be sure that control will transfer to main()
-
-.code32
-.extern kernel_main
-	call kernel_main
-	jmp .
-- 
cgit v1.2.3-18-g5258