From 584f29189dd3ea49577a2159495abd1379c365d5 Mon Sep 17 00:00:00 2001
From: Amelia Coutard <eliottulio.coutard@gmail.com>
Date: Wed, 4 May 2022 13:15:28 +0200
Subject: [PATCH] Added a map to 64TiB of physical memory in the first 64TiB
 (half) of the higher half of memory

---
 src/boot.S | 73 ++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 46 insertions(+), 27 deletions(-)

diff --git a/src/boot.S b/src/boot.S
index 98217be..e745a0f 100644
--- a/src/boot.S
+++ b/src/boot.S
@@ -76,14 +76,18 @@ TSS:
 	IOPB: .short 0
 TSS_END:
 .set TSS_SIZE, TSS_END - TSS
+.align 0x1000
+PDPT_high: .skip 0x1000 - 16
+           .quad 0x83
+           .quad 0x83 + 1024 * 1024 * 1024
 
 .section .bss
 .align 0x1000
 PML4T:     .skip 0x1000
 PDPT_low:  .skip 0x1000
-PDPT_high: .skip 0x1000
 PDT:       .skip 0x1000
 PT:        .skip 0x1000
+phys_mem_map: .skip 0x1000 * 128 - 8
 .align 16
 stack_bottom:
 .skip 1024 * 16 # 16KiB
@@ -95,6 +99,12 @@ stack_top:
 _start:
 	mov $stack_top - KERNEL_VMA, %esp
 
+	# Save multiboot info:
+	push $0   # /
+	push %eax # \ magic
+	push $0   # /
+	push %ebx # \ info structure
+
 	# Check if cpuid is supported:
 	pushfl
 	pop %eax
@@ -108,15 +118,6 @@ _start:
 	popfl
 	xor %ecx, %eax
 	jnz .has_cpuid
-		movw $0x024E, 0xB8000
-		movw $0x026F, 0xB8002
-		movw $0x0220, 0xB8004
-		movw $0x0243, 0xB8006
-		movw $0x0250, 0xB8008
-		movw $0x0255, 0xB800A
-		movw $0x0249, 0xB800C
-		movw $0x0244, 0xB800E
-		movw $0x022E, 0xB8010
 		cli
 	1:	hlt
 		jmp 1b
@@ -129,22 +130,14 @@ _start:
 	jb .no_long_mode
 	mov $0x80000001, %eax
 	cpuid
+	# Long mode:
 	test $1 << 29, %edx
-	jnz .has_long_mode
+	jz .no_long_mode
+	# 1GiB pages:
+	test $1 << 26, %edx
+	jz .no_long_mode
+	jmp .has_long_mode
 	.no_long_mode:
-		movw $0x024E, 0xB8000
-		movw $0x026F, 0xB8002
-		movw $0x0220, 0xB8004
-		movw $0x026C, 0xB8006
-		movw $0x026F, 0xB8008
-		movw $0x026E, 0xB800A
-		movw $0x0267, 0xB800C
-		movw $0x0220, 0xB800E
-		movw $0x026D, 0xB8010
-		movw $0x026F, 0xB8012
-		movw $0x0264, 0xB8014
-		movw $0x0265, 0xB8016
-		movw $0x022E, 0xB8018
 		cli
 	1:	hlt
 		jmp 1b
@@ -164,7 +157,6 @@ _start:
 	mov %eax, PML4T - KERNEL_VMA + 511 * 8
 	mov $PDT - KERNEL_VMA + 3, %eax
 	mov %eax, PDPT_low - KERNEL_VMA + 0 * 8
-	mov %eax, PDPT_high - KERNEL_VMA + 510 * 8
 	mov $PT - KERNEL_VMA + 3, %eax
 	mov %eax, PDT - KERNEL_VMA + 0 * 8
 
@@ -211,16 +203,43 @@ _start:
 
 .code64
 .trampoline:
-	mov %esp, %esp
 	mov $GDT.KERNEL_DATA, %ax  # Set the A-register to the data descriptor.
 	mov %ax, %ds        # Set the data segment to the A-register.
 	mov %ax, %es        # Set the extra segment to the A-register.
 	mov %ax, %fs        # Set the F-segment to the A-register.
 	mov %ax, %gs        # Set the G-segment to the A-register.
 	mov %ax, %ss        # Set the stack segment to the A-register.
+
 	mov $.higher_half, %rax
 	jmp *%rax
 
 .section .text
 .higher_half:
-	call kmain
+	mov %esp, %esp
+	pop %r14 # Multiboot info address.
+	pop %r15 # Multiboot magic.
+	mov $stack_top, %rsp
+
+	# map physical memory in kernel:
+	mov $phys_mem_map - KERNEL_VMA + 3, %rbx
+	mov $PML4T + 256 * 8, %rdi
+	mov $128, %rcx
+1:	mov %rbx, (%rdi)
+	add $0x1000, %rbx
+	add $8, %rdi
+	loop 1b
+
+	mov $0x83, %rbx
+	mov $phys_mem_map, %rdi
+	mov $128 * 512, %rcx
+1:	mov %rbx, (%rdi)
+	add $1024 * 1024 * 1024, %rbx
+	add $8, %rdi
+	loop 1b
+
+	mov $PML4T - KERNEL_VMA, %rax
+	mov %rax, %cr3
+
+	mov %r14, %rsi
+	mov %r15, %rdi
+	call kmain # With the two arguments popped earlier.
-- 
2.47.0