From d00271672b67f2f05d061dcdc7e5c2c8d031f14a Mon Sep 17 00:00:00 2001
From: =?utf8?q?Duje=20Mihanovi=C4=87?= <duje.mihanovic@skole.hr>
Date: Fri, 17 Jun 2022 20:47:51 +0200
Subject: [PATCH] Get memory map from BIOS E820

The entry order is reversed, but otherwise the map makes sense. Also print the
map out to screen.
---
 boot/x86/stage3/e820.s    | 65 +++++++++++++++++++++++++++++++++++++++
 boot/x86/stage3/loader.s  |  3 ++
 include/arch/x86/tty.h    |  1 +
 kernel/arch/x86/tty/tty.c | 38 +++++++++++++++++++++++
 kernel/entry.s            |  2 ++
 kernel/kernel.c           | 27 +++++++++++++++-
 6 files changed, 135 insertions(+), 1 deletion(-)
 create mode 100644 boot/x86/stage3/e820.s

diff --git a/boot/x86/stage3/e820.s b/boot/x86/stage3/e820.s
new file mode 100644
index 0000000..247b361
--- /dev/null
+++ b/boot/x86/stage3/e820.s
@@ -0,0 +1,65 @@
+; Code for getting the BIOS E820 memory map
+
+bits 16
+
+; Return: ECX - number of entries, DI - pointer to map
+get_e820_map:
+	push eax
+	push ebx
+	push edx
+	push esi
+	push es
+
+	xor ax, ax
+	mov es, ax
+	push dword 1
+	sub sp, 20
+	xor si, si
+	xor ebx, ebx
+	mov edx, 0x534d4150
+	mov eax, 0xe820
+	mov ecx, 24
+	mov di, sp
+	int 0x15
+	jc .no_e820
+	cmp eax, 0x534d4150
+	jne .unexpected
+	inc si
+	.loop:
+		push dword 1
+		sub sp, 20
+		mov di, sp
+		mov eax, 0xe820
+		mov ecx, 24
+		int 0x15
+		jc .carry_done
+		inc si
+		cmp ebx, 0
+		je .done
+		jmp .loop
+	.carry_done:
+		add sp, 24
+	.done:
+		movzx ecx, si
+		movzx edi, sp
+		mov ax, 24
+		mul si
+		add sp, ax
+		pop es
+		pop esi
+		pop edx
+		pop ebx
+		pop eax
+		ret
+	.no_e820:
+		print no_e820
+		hlt
+		jmp $-1
+	.unexpected
+		print e820_unexpected
+		call print_dword
+		hlt
+		jmp $-1
+
+no_e820: db "BIOS does not support E820, cannot proceed!", 0xd, 0xa, 0
+e820_unexpected: db "Unexpected value in EAX after getting map entry: expected SMAP, got ", 0
diff --git a/boot/x86/stage3/loader.s b/boot/x86/stage3/loader.s
index 2967c6e..0ca0ea6 100644
--- a/boot/x86/stage3/loader.s
+++ b/boot/x86/stage3/loader.s
@@ -64,6 +64,8 @@ _start:
 	call read_clus_chain_unreal ; load kernel
 	print kernel_loaded
 	
+	call get_e820_map
+
 	cli
 	lgdt [gdt]
 	mov eax, cr0
@@ -151,6 +153,7 @@ memcpy:
 %include "../fat32/fat32.s"
 %include "gdt.s"
 %include "print.s"
+%include "e820.s"
 
 in_protected:
 bits 32
diff --git a/include/arch/x86/tty.h b/include/arch/x86/tty.h
index 2224737..ce49da9 100644
--- a/include/arch/x86/tty.h
+++ b/include/arch/x86/tty.h
@@ -25,4 +25,5 @@ extern void kprint(const char *string, uint8_t color);
 extern void kprintb(const uint8_t byte);
 extern void kprintw(const uint16_t word);
 extern void kprintd(const uint32_t dword);
+extern void kprintq(const uint64_t qword);
 #endif
diff --git a/kernel/arch/x86/tty/tty.c b/kernel/arch/x86/tty/tty.c
index 07d734e..2110a7d 100644
--- a/kernel/arch/x86/tty/tty.c
+++ b/kernel/arch/x86/tty/tty.c
@@ -137,3 +137,41 @@ void kprintd(uint32_t dword)
 	temp = dword & 0xF;
 	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
 }
+
+void kprintq(uint64_t qword)
+{
+	uint8_t temp;
+	temp = qword >> 60;
+	kprint("0x", VGA_COLOR_LIGHT_GRAY);
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 56) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 52) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 48) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 44) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 40) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 36) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 32) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 28) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 24) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 20) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 16) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 12) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 8) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = (qword >> 4) & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+	temp = qword & 0xF;
+	kprintc(hex_chars[temp], VGA_COLOR_LIGHT_GRAY);
+}
diff --git a/kernel/entry.s b/kernel/entry.s
index 10c95e8..5ef71bb 100644
--- a/kernel/entry.s
+++ b/kernel/entry.s
@@ -6,6 +6,8 @@ global _start
 _start:
 	mov ebp, __STACK_BOTTOM__
 	mov esp, ebp
+	push ecx
+	push edi
 	call kmain
 	hlt
 	jmp $-1
diff --git a/kernel/kernel.c b/kernel/kernel.c
index 060051c..0aa8fc2 100644
--- a/kernel/kernel.c
+++ b/kernel/kernel.c
@@ -11,13 +11,38 @@ extern void pf_handler(struct fault_frame *frame);
 static struct idt_descriptor idt[256] __attribute__((aligned(0x10)));
 static struct idtr idtr __attribute__((aligned(0x10)));
 
+struct e820_map {
+	uint64_t base;
+	uint64_t length;
+	uint32_t type;
+	uint32_t attrib;
+};
 
-void kmain(void)
+void print_e820(struct e820_map *mmap, int mmap_size)
+{
+	kprint("       Base       |      Length      |   Type   |  Attrib  |\n", 0);
+	kprint("------------------------------------------------------------\n", 0);
+	for (int i=0; i<mmap_size; i++) {
+		kprintq(mmap[i].base);
+		kprintc('|', 0);
+		kprintq(mmap[i].length);
+		kprintc('|', 0);
+		kprintd(mmap[i].type);
+		kprintc('|', 0);
+		kprintd(mmap[i].attrib);
+		kprintc('|', 0);
+		kprintc('\n', 0);
+	}
+}
+
+void kmain(struct e820_map *mmap, int mmap_size)
 {
 	screen_clear();
 	kprint("Welcome to Nameless OS!\nRunning revision: ", 0);
 	kprint(GIT_COMMIT, 0);
 	kprint("\n", 0);
+	kprint("BIOS memory map:\n", 0);
+	print_e820(mmap, mmap_size);
 	kprint("Preparing IDT...\n", 0);
 	idt_set_descriptor(idt, 8, 0x8, (uint32_t) double_fault, IDT_INTERRUPT_GATE, 0x0);
 	idt_set_descriptor(idt, 14, 0x8, (uint32_t) pf_handler, IDT_INTERRUPT_GATE, 0x0);
-- 
2.39.2