From 0614eb0a414311e652391d1eb08b97e1129871c2 Mon Sep 17 00:00:00 2001
From: Tianhao Wang <shrik3@mailbox.org>
Date: Thu, 18 Apr 2024 03:21:50 +0200
Subject: startup: flatten control flow

---
 boot/startup-x86_64.s | 39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

(limited to 'boot')

diff --git a/boot/startup-x86_64.s b/boot/startup-x86_64.s
index 5413a80..3a8de41 100644
--- a/boot/startup-x86_64.s
+++ b/boot/startup-x86_64.s
@@ -95,28 +95,8 @@ init_longmode:
 	or	   eax, 1 << 5
 	mov    cr4, eax
 
-	; create page table (mandatory)
-	call   setup_paging
-
-	; activate Long Mode (for now in compatibility mode)
-	mov    ecx, 0x0C0000080 ; select EFER (Extended Feature Enable Register)
-	rdmsr
-	or	   eax, 1 << 8 ; LME (Long Mode Enable)
-	wrmsr
-
-	; activate paging
-	mov    eax, cr0
-	or	   eax, 1 << 31
-	mov    cr0, eax
-
-	; jump to 64-bit code segment -> full activation of Long Mode
-	jmp    2 * 0x8 : longmode_start
-
-;
-; Provisional identical page mapping, using 1G huge page (therefore only 2 table
-; levels needed)
-;
-
+	; Provisional identical page mapping, using 1G huge page (therefore only 2 table
+	; levels needed)
 setup_paging:
 	; PML4 (Page Map Level 4 / 1st level)
 	mov    eax, pdp
@@ -141,7 +121,20 @@ fill_tables2_done:
 	; set base pointer to PML4
 	mov    eax, pml4
 	mov    cr3, eax
-	ret
+activate_long_mode:
+	; activate Long Mode (for now in compatibility mode)
+	mov    ecx, 0x0C0000080 ; select EFER (Extended Feature Enable Register)
+	rdmsr
+	or	   eax, 1 << 8 ; LME (Long Mode Enable)
+	wrmsr
+	; activate paging
+	mov    eax, cr0
+	or	   eax, 1 << 31
+	mov    cr0, eax
+
+	; jump to 64-bit code segment -> full activation of Long Mode
+	jmp    2 * 0x8 : longmode_start
+
 
 ;
 ;	system start, part 2 (in 64-bit Long Mode)
-- 
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