GP Fault handler

Reviewed-on: #7

.gitignore

@@ -1,5 +1,9 @@
 limine
 kernel
+pepperk
 iso_root
 *.o
 *.iso
+*.gch
+*/*.gch
+*/*/*.gch

Makefile

@@ -1,8 +1,11 @@
+SOURCES = src/mem/heap/kheap.c src/mem/paging/vmm.c src/mem/paging/paging.c src/mem/paging/pmm.c src/string/string.c src/io/kbd/ps2.c src/io/serial/serial.c src/io/term/printf.c src/io/term/term.c src/idt/idt.c src/mem/gdt/gdt.c src/mem/misc/utils.c src/time/timer.c src/kmain.c
+
 build:
 	rm -f *.o
-	x86_64-elf-gcc -c -I src src/io/term.c src/io/printf.c src/kmain.c -Wall -Wextra -std=gnu99 -nostdlib -ffreestanding -fno-stack-protector -fno-stack-check -fno-PIC -ffunction-sections -fdata-sections -mcmodel=kernel
+	x86_64-elf-gcc -g -c -Isrc $(SOURCES) -Wall -Wextra -std=gnu99 -nostdlib -ffreestanding -fno-stack-protector -fno-stack-check -fno-PIC -ffunction-sections -fdata-sections -mcmodel=kernel
 	objcopy -O elf64-x86-64 -B i386 -I binary zap-light16.psf zap-light16.o
-	x86_64-elf-ld -o kernel -T linker.ld *.o
+	nasm -f elf64 src/idt/idt.S -o idt_stub.o
+	x86_64-elf-ld -o pepperk -T linker.ld *.o
 
 limine/limine:
 	rm -rf limine
@@ -12,7 +15,7 @@ limine/limine:
 build-iso: limine/limine build
 	rm -rf iso_root
 	mkdir -p iso_root/boot
-	cp -v kernel iso_root/boot
+	cp -v pepperk iso_root/boot
 	mkdir -p iso_root/boot/limine
 	cp -v limine.conf iso_root/boot/limine
 	mkdir -p iso_root/EFI/BOOT
@@ -23,11 +26,15 @@ build-iso: limine/limine build
 		-no-emul-boot -boot-load-size 4 -boot-info-table -hfsplus \
 		-apm-block-size 2048 --efi-boot boot/limine/limine-uefi-cd.bin \
 		-efi-boot-part --efi-boot-image --protective-msdos-label \
-		iso_root -o kernel.iso
-	./limine/limine bios-install kernel.iso
+		iso_root -o pepper.iso
+	./limine/limine bios-install pepper.iso
+
+debug:
+	qemu-system-x86_64 -drive file=pepper.iso -s -S -d int -no-reboot -no-shutdown &
+	gdb pepperk --command=debug.gdb
 
 run: build-iso
-	qemu-system-x86_64 -cdrom kernel.iso
+	qemu-system-x86_64 -cdrom pepper.iso -serial stdio
 
 clean:
-	rm -rf *.o kernel iso_root kernel.iso limine
+	rm -rf *.o pepperk iso_root pepper.iso limine

README.md

@@ -1,4 +1,4 @@
-# pepperOS: "will never be done"
+# <img width="40" height="40" alt="red-pepper" src="https://i.ibb.co/mrHH6d1m/pixil-frame-0-4.png" /> pepperOS: "will never be done"
 
 ## Trying the kernel
 
@@ -7,6 +7,25 @@ First install the dependencies: `sudo apt install xorriso make qemu-system`
 Then, to compile the kernel and make an ISO image file: `make build-iso`
 To run it with QEMU, `make run`
 
+## TODO
+
+The basics that I'm targeting are:
+
+- Fix terminal driver (backspace issues, scrolling) OR add Flanterm or equivalent
+- Implement paging / see what Limine does at boot with memory management
+- Implement tasks, and task switching
+- Load an executable
+- Scheduler (round-robin using the PIT timer interrupt)
+- Filesystem (TAR for read-only initfs, then maybe read-write using FAT12/16/32
+- Getting to userspace (syscalls)
+- Porting musl libc or equivalent
+
+In the future, maybe?
+
+- SMP support
+- Parsing the ACPI tables and using them for something
+- Replacing the PIT timer with APIC
+
 ## Thanks
 
 PepperOS wouldn't be possible without the following freely-licensed software:
@@ -14,3 +33,7 @@ PepperOS wouldn't be possible without the following freely-licensed software:
 - the [Limine](https://codeberg.org/Limine/Limine) portable bootloader
 - Marco Paland's freestanding [printf implementation](https://github.com/mpaland)
 - the [ZAP](https://www.zap.org.au/projects/console-fonts-zap/) PSF console fonts
+
+...and without these amazing resources:
+
+- the [OSDev](https://osdev.org) wiki & forums

debug.gdb

@@ -0,0 +1,3 @@
+target remote localhost:1234
+set disassembly-flavor intel
+display/8i $rip

limine.conf

@@ -3,4 +3,4 @@ timeout: 3
 /PepperOS
 	protocol: limine
 
-	path: boot():/boot/kernel
+	path: boot():/boot/pepperk

src/idt/idt.S

@@ -0,0 +1,310 @@
+; Assembly stub for the IDT
+
+bits 64
+
+extern interrupt_dispatch
+
+global interrupt_stub
+global vector_0_handler
+global vector_1_handler
+global vector_2_handler
+global vector_3_handler
+global vector_4_handler
+global vector_5_handler
+global vector_6_handler
+global vector_7_handler
+global vector_8_handler
+global vector_9_handler
+global vector_10_handler
+global vector_11_handler
+global vector_12_handler
+global vector_13_handler
+global vector_14_handler
+global vector_15_handler
+global vector_16_handler
+global vector_17_handler
+global vector_18_handler
+global vector_19_handler
+global vector_20_handler
+global vector_21_handler
+
+interrupt_stub:
+    ; We'll push all general-purpose registers to the stack,
+    ; so they're intact and don't bother the code that was
+    ; executed when the interrupt happened.
+    ; (except rsp because it will already be saved in the iret frame)
+    
+    push qword rax
+    push qword rbx
+    push qword rcx
+    push qword rdx
+    push qword rsi 
+    push qword rdi
+    ;push qword rsp
+    push qword rbp
+    push qword r8
+    push qword r9
+    push qword r10
+    push qword r11
+    push qword r12
+    push qword r13
+    push qword r14
+    push qword r15
+
+    ; Put stack pointer as first argument of our function
+    mov rdi, rsp
+    call interrupt_dispatch
+    ; What the function returns (new stack pointer) is saved in rbp
+    mov rsp, rax
+
+    pop qword r15
+    pop qword r14
+    pop qword r13
+    pop qword r12
+    pop qword r11
+    pop qword r10
+    pop qword r9
+    pop qword r8
+    pop qword rbp
+    ;pop qword rsp
+    pop qword rdi
+    pop qword rsi
+    pop qword rdx
+    pop qword rcx
+    pop qword rbx
+    pop qword rax
+
+    ; Removing the error code and vector number so stack doesn't
+    ; get corrupted
+    add rsp, 16
+    
+    ; Restore ss, rsp, rflags, cs, rip of code that was executing
+    ; before the interrupt
+    iretq
+
+; Vector handlers will be 16-byte aligned so that we can loop over them
+; like <vector_no> * 16 to get each one's address
+
+; Divide Error
+align 16
+vector_0_handler:
+    ; error code (nothing, so we push a dummy 0 quadword, 64bits/8bytes long)
+    push qword 0
+    ; vector number (so our interrupt stub knows which one it is)
+    push qword 0
+    jmp interrupt_stub
+
+; Debug Exception
+align 16
+vector_1_handler:
+    push qword 0
+    push qword 1
+    jmp interrupt_stub
+
+; NMI
+align 16
+vector_2_handler:
+    push qword 0
+    push qword 2
+    jmp interrupt_stub
+
+; Breakpoint
+align 16
+vector_3_handler:
+    push qword 0
+    push qword 3
+    jmp interrupt_stub
+
+; Overflow
+align 16
+vector_4_handler:
+    push qword 0
+    push qword 4
+    jmp interrupt_stub
+
+; BOUND Range exceeded
+align 16
+vector_5_handler:
+    push qword 0
+    push qword 5
+    jmp interrupt_stub
+
+; Invalid Opcode
+align 16
+vector_6_handler:
+    push qword 0
+    push qword 6
+    jmp interrupt_stub
+
+; Device Not Available
+align 16
+vector_7_handler:
+    push qword 0
+    push qword 7
+    jmp interrupt_stub
+
+; Double Fault
+align 16
+vector_8_handler:
+    ; No error code, we only push vector number
+    push qword 1
+    jmp interrupt_stub
+
+; Coprocessor Segment Overrun
+align 16
+vector_9_handler:
+    push qword 9
+    jmp interrupt_stub
+
+; Invalid TSS
+align 16
+vector_10_handler:
+    push qword 10
+    jmp interrupt_stub
+
+; Segment Not Present
+align 16
+vector_11_handler:
+    push qword 11
+    jmp interrupt_stub
+
+; Stack-Segment Fault
+align 16
+vector_12_handler:
+    push qword 12
+    jmp interrupt_stub
+
+; General Protection
+align 16
+vector_13_handler:
+    push qword 13
+    jmp interrupt_stub
+
+; Page Fault
+align 16
+vector_14_handler:
+    push qword 14
+    jmp interrupt_stub
+
+; Intel reserved
+align 16
+vector_15_handler:
+    push qword 0
+    push qword 15
+    jmp interrupt_stub
+
+; x87 FPU Floating-Point Error
+align 16
+vector_16_handler:
+    push qword 0
+    push qword 16
+    jmp interrupt_stub
+
+; Alignment Check
+align 16
+vector_17_handler:
+    push qword 17
+    jmp interrupt_stub
+
+; Machine Check
+align 16
+vector_18_handler:
+    push qword 0
+    push qword 18
+    jmp interrupt_stub
+
+; SIMD Floating-Point Exception
+align 16
+vector_19_handler:
+    push qword 0
+    push qword 19
+    jmp interrupt_stub
+
+; Virtualization Exception
+align 16
+vector_20_handler:
+    push qword 0
+    push qword 20
+    jmp interrupt_stub
+
+; Control Protection Exception
+align 16
+vector_21_handler:
+    push qword 21
+    jmp interrupt_stub
+
+; The others are reserved (22->31) or external (32->255) interrupts
+
+align 16
+vector_22_handler:
+    push qword 0
+    push qword 22
+    jmp interrupt_stub
+
+align 16
+vector_23_handler:
+    push qword 0
+    push qword 23
+    jmp interrupt_stub
+
+align 16
+vector_24_handler:
+    push qword 0
+    push qword 24
+    jmp interrupt_stub
+
+align 16
+vector_25_handler:
+    push qword 0
+    push qword 25
+    jmp interrupt_stub
+
+align 16
+vector_26_handler:
+    push qword 0
+    push qword 26
+    jmp interrupt_stub
+
+align 16
+vector_27_handler:
+    push qword 0
+    push qword 27
+    jmp interrupt_stub
+
+align 16
+vector_28_handler:
+    push qword 0
+    push qword 28
+    jmp interrupt_stub
+
+align 16
+vector_29_handler:
+    push qword 0
+    push qword 29
+    jmp interrupt_stub
+
+align 16
+vector_30_handler:
+    push qword 0
+    push qword 30
+    jmp interrupt_stub
+
+align 16
+vector_31_handler:
+    push qword 0
+    push qword 31
+    jmp interrupt_stub
+
+; PIT timer
+align 16
+vector_32_handler:
+    push qword 0
+    push qword 32
+    jmp interrupt_stub
+
+; PS/2 Keyboard
+align 16
+vector_33_handler:
+    push qword 0
+    push qword 33
+    jmp interrupt_stub

src/idt/idt.c

@@ -0,0 +1,204 @@
+#include "idt.h"
+#include <stdint.h>
+#include <stddef.h>
+#include "io/serial/serial.h"
+#include "io/kbd/ps2.h"
+#include <kernel.h>
+#include <stdbool.h>
+
+struct interrupt_descriptor idt[256];
+struct idtr idt_reg;
+
+// Address to our first interrupt handler
+extern char vector_0_handler[];
+
+// Timer ticks
+extern uint64_t ticks;
+
+void idt_set_entry(uint8_t vector, void* handler, uint8_t dpl)
+{
+    uint64_t handler_addr = (uint64_t)handler;
+
+    struct interrupt_descriptor* entry = &idt[vector];
+    // Address is split in three parts so we right-shift progressively to get it all
+    entry->address_low = handler_addr & 0xFFFF;
+    entry->address_mid = (handler_addr >> 16) & 0xFFFF;
+    entry->address_high = handler_addr >> 32;
+
+    // Kernel code selector (as set in GDT)
+    entry->selector = 0x8;
+    // Interrupt gate, present, DPL (having: max DPL = 3)
+    entry->flags = 0b1110 | ((dpl & 0b11) << 5) | (1 << 7);
+    // We won't use IST for now
+    entry->ist = 0;
+}
+
+void idt_load(void* idt_addr)
+{
+    // "limit" = "size" = Size of the IDT - 1 byte = (16*256)-1 = 0xFFF
+    idt_reg.limit = 0xFFF;
+    idt_reg.base = (uint64_t)idt_addr;
+    asm volatile("lidt %0" :: "m"(idt_reg));
+}
+
+void idt_init()
+{
+    // We set 256 entries, but we have only the first few stubs.
+    // Undefined behavior?
+    for (size_t i=0; i<256; i++)
+    {
+        // Each vector handler is 16-byte aligned, so <vector_no>*16 = address of that handler
+        idt_set_entry(i, vector_0_handler + (i*16), 0);
+    }
+    idt_load(&idt);
+    DEBUG("IDT initialized");
+}
+
+static inline uint64_t read_cr2(void)
+{
+    uint64_t val;
+    asm volatile ("mov %%cr2, %0" : "=r"(val));
+    return val;
+}
+
+static void page_fault_handler(struct cpu_status_t* ctx)
+{
+    // It could be used to remap pages etc. to fix the fault, but right now what I'm more
+    // interested in is getting more info out of those numbers cause i'm lost each time i have 
+    // to read all this mess
+    uint64_t cr2 = read_cr2();
+    
+    DEBUG("\x1b[38;5;231mPage Fault at rip=0x%p, err=%u (%s%s%s%s%s%s%s%s) when accessing addr=0x%p\x1b[0m", ctx->iret_rip, ctx->error_code,
+    CHECK_BIT(ctx->error_code, 0) ? "PAGE_PROTECTION_VIOLATION " : "PAGE_NOT_PRESENT ",
+    CHECK_BIT(ctx->error_code, 1) ? "ON_WRITE " : "ON_READ ",
+    CHECK_BIT(ctx->error_code, 2) ? "IN_USER_MODE" : "IN_KERNEL_MODE",
+    CHECK_BIT(ctx->error_code, 3) ? " WAS_RESERVED" : "",
+    CHECK_BIT(ctx->error_code, 4) ? " ON_INSTRUCTION_FETCH" : "",
+    CHECK_BIT(ctx->error_code, 5) ? " PK_VIOLATION" : "",
+    CHECK_BIT(ctx->error_code, 6) ? " ON_SHADOWSTACK_ACCESS" : "",
+    CHECK_BIT(ctx->error_code, 7) ? " SGX_VIOLATION" : "",
+    cr2);
+
+    /* if (CHECK_BIT(ctx->error_code, 0))
+    {
+        panic(ctx);
+    } */
+    panic(ctx);
+}
+
+static void gp_fault_handler(struct cpu_status_t* ctx)
+{
+    DEBUG("\x1b[38;5;231mGeneral Protection Fault at rip=0x%p, err=%u (%s)\x1b[0m",
+    ctx->iret_rip,
+    ctx->error_code,
+    (ctx->error_code == 0) ? "NOT_SEGMENT_RELATED" : "SEGMENT_RELATED");
+
+    // Segment-related
+    if (ctx->error_code != 0)
+    {
+        bool is_external = CHECK_BIT(ctx->error_code, 0);
+        // is it IDT, GDT, LDT?
+        uint8_t table = ctx->error_code & 0x6; // 0b110 (isolate table)
+        uint16_t index = ctx->error_code & 0xFFF8; // 13*1 1111111111111 + 000 = 1111111111111000
+    
+        char* table_names[4] = {"GDT", "IDT", "LDT", "IDT"};
+
+        DEBUG("\x1b[38;5;231m%s in %s index %u\x1b[0m",
+        is_external ? "EXTERNAL" : "INTERNAL",
+        table_names[table],
+        index);
+    }
+
+    panic(ctx);
+}
+
+struct cpu_status_t* interrupt_dispatch(struct cpu_status_t* context)
+{
+    switch(context->vector_number)
+    {
+        case 0:
+            DEBUG("Divide Error!");
+            break;
+        case 1:
+            DEBUG("Debug Exception!");
+            break;
+        case 2:
+            DEBUG("NMI Interrupt!");
+            break;
+        case 3:
+            DEBUG("Breakpoint Interrupt!");
+            break;
+        case 4:
+            DEBUG("Overflow Trap!");
+            break;
+        case 5:
+            DEBUG("BOUND Range Exceeded!");
+            break;
+        case 6:
+            DEBUG("Invalid Opcode!");
+            break;
+        case 7:
+            DEBUG("Device Not Available!");
+            break;
+        case 8:
+            DEBUG("Double Fault!");
+            break;
+        case 9:
+            DEBUG("Coprocessor Segment Overrun!");
+            break;
+        case 10:
+            DEBUG("Invalid TSS!");
+            break;
+        case 11:
+            DEBUG("Segment Not Present!");
+            break;
+        case 12:
+            DEBUG("Stack-Segment Fault!");
+            break;
+        case 13:
+            gp_fault_handler(context);
+            break;
+        case 14:
+            // Better debugging for page faults...
+            page_fault_handler(context);
+            break;
+        case 15:
+            DEBUG("Intel Reserved Interrupt! (Achievement unlocked: How Did We Get Here?)");
+            break;
+        case 16:
+            DEBUG("x87 Floating-Point Error!");
+            break;
+        case 17:
+            DEBUG("Alignment Check Fault!");
+            break;
+        case 18:
+            DEBUG("Machine Check!");
+            break;
+        case 19:
+            DEBUG("SIMD Floating-Point Exception!");
+            break;
+        case 20:
+            DEBUG("Virtualization Exception!");
+            break;
+        case 21:
+            DEBUG("Control Protection Exception!");
+            break;
+
+        case 32:
+            //DEBUG("Tick!");
+            ticks++;
+            // Send an EOI so that we can continue having interrupts
+            outb(0x20, 0x20);
+            break;
+
+        case 33:
+            keyboard_handler();
+            break;
+
+        default:
+            DEBUG("Unexpected interrupt");
+            break;
+    }
+
+    return context;
+}

src/idt/idt.h

@@ -0,0 +1,57 @@
+#ifndef IDT_H
+#define IDT_H
+
+#include <stdint.h>
+
+void idt_init();
+
+struct interrupt_descriptor
+{
+    uint16_t address_low;
+    uint16_t selector;
+    uint8_t ist;
+    uint8_t flags;
+    uint16_t address_mid;
+    uint32_t address_high;
+    uint32_t reserved;
+} __attribute__((packed));
+
+struct idtr 
+{
+    uint16_t limit;
+    uint64_t base;
+} __attribute__((packed));
+
+// All general-purpose registers (except rsp) as stored on the stack,
+// plus the values we pushed (vector number, error code) and the iret frame
+// In reverse order because the stack grows downwards.
+struct cpu_status_t
+{
+    uint64_t r15;
+    uint64_t r14;
+    uint64_t r13;
+    uint64_t r12;
+    uint64_t r11;
+    uint64_t r10;
+    uint64_t r9;
+    uint64_t r8;
+    uint64_t rbp;
+    //uint64_t rsp;
+    uint64_t rdi;
+    uint64_t rsi;
+    uint64_t rdx;
+    uint64_t rcx;
+    uint64_t rbx;
+    uint64_t rax;
+
+    uint64_t vector_number;
+    uint64_t error_code;
+
+    uint64_t iret_rip;
+    uint64_t iret_cs;
+    uint64_t iret_flags;
+    uint64_t iret_rsp;
+    uint64_t iret_ss;
+};
+
+#endif

src/io/kbd/ps2.c

@@ -0,0 +1,237 @@
+// PS/2 Keyboard support
+
+#include "io/serial/serial.h"
+#include "ps2.h"
+#include <stdint.h>
+#include "io/term/term.h"
+#include <kernel.h>
+
+// The key status bitfield will be used to see if ALT, CONTROL, or SHIFT is pressed
+uint8_t key_status = 0b00000000;
+
+// Keymap pointers so we can change between different layouts
+unsigned char* keymap;
+unsigned char* keymap_shifted;
+
+unsigned char kbdus[128] =
+{
+    0,  27, '1', '2', '3', '4', '5', '6', '7', '8',	/* 9 */
+    '9', '0', '-', '=', '\b',	/* Backspace */
+    '\t', /* Tab */
+    'q', 'w', 'e', 'r',	/* 19 */
+    't', 'y', 'u', 'i', 'o', 'p', '[', ']', '\n',	/* Enter key */
+    CTRL,			/* 29   - Control */
+    'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l', ';',	/* 39 */
+    '\'', '`',   SHIFT,		/* Left shift */
+    '\\', 'z', 'x', 'c', 'v', 'b', 'n',			/* 49 */
+    'm', ',', '.', '/',   SHIFT,				/* Right shift */
+    '*',
+    ALT,	/* Alt */
+  ' ',	/* Space bar */
+    0,	/* Caps lock */
+    0,	/* 59 - F1 key ... > */
+    0,   0,   0,   0,   0,   0,   0,   0,
+    0,	/* < ... F10 */
+    0,	/* 69 - Num lock*/
+    0,	/* Scroll Lock */
+    0,	/* Home key */
+    0,	/* Up Arrow */
+    0,	/* Page Up */
+    '-',
+    0,	/* Left Arrow */
+    0,
+    0,	/* Right Arrow */
+    '+',
+    0,	/* 79 - End key*/
+    0,	/* Down Arrow */
+    0,	/* Page Down */
+    0,	/* Insert Key */
+    0,	/* Delete Key */
+    0,   0,   0,
+    0,	/* F11 Key */
+    0,	/* F12 Key */
+    0,	/* All other keys are undefined */
+};
+
+unsigned char kbdus_shifted[128] =
+{
+    0,  27, '!', '@', '#', '$', '%', '^', '&', '*',   /* 9 */
+    '(', ')', '_', '+', '\b',                        /* Backspace */
+    '\t',                                            /* Tab */
+    'Q', 'W', 'E', 'R',                               /* 19 */
+    'T', 'Y', 'U', 'I', 'O', 'P', '{', '}', '\n',     /* Enter */
+    CTRL,                                            /* 29 */
+    'A', 'S', 'D', 'F', 'G', 'H', 'J', 'K', 'L', ':', /* 39 */
+    '"', '~', SHIFT,                                 /* Left shift */
+    '|', 'Z', 'X', 'C', 'V', 'B', 'N',                /* 49 */
+    'M', '<', '>', '?', SHIFT,                        /* Right shift */
+    '*',
+    ALT,                                             /* Alt */
+    ' ',                                             /* Space */
+    0,                                               /* Caps lock */
+    0, 0, 0, 0, 0, 0, 0, 0,
+    0,                                               /* F10 */
+    0,                                               /* Num lock */
+    0,                                               /* Scroll lock */
+    0, 0, 0,
+    '-',
+    0, 0, 0,
+    '+',
+    0, 0, 0,
+    0, 0,
+    0, 0, 0,
+    0,                                               /* F11 */
+    0                                                /* F12 */
+};
+
+// NOT THE REAL FR KEYMAP!!
+// Some French keys have accents or weird symbols that aren't part of ASCII
+// so they won't fit in 1 char. As a substitute for now, these will be
+// changed to their ASCII counterparts (without accents, etc.)
+unsigned char kbdfr[128] =
+{
+    0,  27, '&', 'e', '"', '\'', '(', '-', 'e', '_',
+    'c', 'a', ')', '=', '\b',
+    '\t',
+    'a', 'z', 'e', 'r',
+    't', 'y', 'u', 'i', 'o', 'p', '^', '$', '\n',
+    CTRL,
+    'q', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l', 'm',
+    'u', '`', SHIFT,
+    '*', 'w', 'x', 'c', 'v', 'b', 'n',
+    ',', ';', ':', '!', SHIFT,
+    '*',
+    ALT,
+    ' ',
+    0,
+    0, 0, 0, 0, 0, 0, 0, 0,
+    0,
+    0,
+    0,
+    0, 0, 0,
+    '-',
+    0, 0, 0,
+    '+',
+    0, 0, 0,
+    0, 0,
+    0, 0, 0,
+    0,
+    0
+};
+
+unsigned char kbdfr_shifted[128] =
+{
+    0,  27, '1', '2', '3', '4', '5', '6', '7', '8',
+    '9', '0', '^', '+', '\b',
+    '\t',
+    'A', 'Z', 'E', 'R',
+    'T', 'Y', 'U', 'I', 'O', 'P', '^', 'L', '\n',
+    CTRL,
+    'Q', 'S', 'D', 'F', 'G', 'H', 'J', 'K', 'L', 'M',
+    '%', '~', SHIFT,
+    'u', 'W', 'X', 'C', 'V', 'B', 'N',
+    '?', '.', '/', 'S', SHIFT,
+    '*',
+    ALT,
+    ' ',
+    0,
+    0, 0, 0, 0, 0, 0, 0, 0,
+    0,
+    0,
+    0,
+    0, 0, 0,
+    '-',
+    0, 0, 0,
+    '+',
+    0, 0, 0,
+    0, 0,
+    0, 0, 0,
+    0,
+    0
+};
+
+void keyboard_handler()
+{
+    unsigned char scancode = inb(0x60);
+
+    // Key release (bit 7 set)
+    if (scancode & 0x80)
+    {
+        unsigned char code = scancode & 0x7F;
+        switch (code)
+        {
+            // Clear the corresponding bit if corresponding key is released
+            case LEFT_SHIFT_PRESSED:
+            case RIGHT_SHIFT_PRESSED:
+                key_status &= ~SHIFT_PRESSED_BIT;
+                break;
+            case CTRL_PRESSED:
+                key_status &= ~CTRL_PRESSED_BIT;
+                break;
+            case ALT_PRESSED:
+                key_status &= ~ALT_PRESSED_BIT;
+                break;
+        }
+
+        // Send EOI
+        outb(0x20, 0x20);
+        return;
+    }
+    else
+    {
+        // Key press
+        switch (scancode)
+        {
+            // Set bits for corresponding special key press
+            case LEFT_SHIFT_PRESSED:
+            case RIGHT_SHIFT_PRESSED:
+                key_status |= SHIFT_PRESSED_BIT;
+                break;
+            case CTRL_PRESSED:
+                key_status |= CTRL_PRESSED_BIT;
+                break;
+            case ALT_PRESSED:
+                key_status |= ALT_PRESSED_BIT;
+                break;
+
+            default:
+            {
+                // Should we get a SHIFTED char or a regular one?
+                unsigned char c = (key_status & SHIFT_PRESSED_BIT) ? keymap_shifted[scancode] : keymap[scancode];
+
+                if (c)
+                {
+                    putchar(c);
+                }
+            }
+        }
+
+        skputs("key pressed!\n");
+    }
+
+    // End of Interrupt (to master PIC)
+    outb(0x20, 0x20);
+}
+
+void keyboard_init(unsigned char layout)
+{
+    // Here we might go and select PS/2, USB, or other... (once we implement multiple keyboard protocols)
+
+    // Keyboard layout selection
+    switch (layout)
+    {
+        case US:
+            keymap = kbdus;
+            keymap_shifted = kbdus_shifted;
+            break;
+        case FR:
+            keymap = kbdfr;
+            keymap_shifted = kbdfr_shifted;
+            break;
+        
+        default:
+            skputs("Unsupported layout.");
+            return;
+    }
+    DEBUG("PS/2 Keyboard initialized");
+}

src/io/kbd/ps2.h

@@ -0,0 +1,37 @@
+#ifndef PS2_H
+#define PS2_H
+
+void keyboard_handler();
+
+#define SHIFT_PRESSED_BIT 0b00000001
+#define ALT_PRESSED_BIT   0b00000010
+#define CTRL_PRESSED_BIT  0b00000100
+
+enum SpecialKeys
+{
+    SHIFT = 255,
+    ALT = 254,
+    CTRL = 253
+};
+
+enum SpecialScancodes
+{
+    LEFT_SHIFT_PRESSED = 0x2A,
+    LEFT_SHIFT_RELEASED = 0xAA,
+    RIGHT_SHIFT_PRESSED = 0x36,
+    RIGHT_SHIFT_RELEASED = 0xB6,
+    CTRL_PRESSED = 0x1D,
+    CTRL_RELEASED = 0x9D,
+    ALT_PRESSED = 0x38,
+    ALT_RELEASED = 0xB8  
+};
+
+enum KeyboardLayout
+{
+    US,
+    FR  
+};
+
+void keyboard_init(unsigned char layout);
+
+#endif

src/io/serial/serial.c

@@ -0,0 +1,64 @@
+#include <kernel.h>
+#include "serial.h"
+
+void outb(int port, unsigned char data)
+{
+    __asm__ __volatile__("outb %%al, %%dx" :: "a" (data),"d" (port));
+}
+
+unsigned char inb(int port)
+{
+    unsigned char data = 0;
+    __asm__ __volatile__("inb %%dx, %%al" : "=a" (data) : "d" (port));
+    return data;
+}
+
+// COM1
+#define PORT 0x3F8
+
+int serial_init()
+{
+    outb(PORT + 1, 0x00);      // Disable all interrupts
+    outb(PORT + 3, 0x80);    // Enable DLAB (set baud rate divisor)
+    outb(PORT + 0, 0x03);    // Set divisor to 3 (lo byte) 38400 baud
+    outb(PORT + 1, 0x00);    //                  (hi byte)
+    outb(PORT + 3, 0x03);    // 8 bits, no parity, one stop bit
+    outb(PORT + 2, 0xC7);    // Enable FIFO, clear them, with 14-byte threshold
+    outb(PORT + 4, 0x0B);    // IRQs enabled, RTS/DSR set
+    outb(PORT + 4, 0x1E);    // Set in loopback mode, test the serial chip
+    outb(PORT + 0, 0xAE);    // Test serial chip (send byte 0xAE and check if serial returns same byte)
+
+    if (inb(PORT) != 0xAE)
+    {
+        return -EIO;
+    }
+
+    // Set normal operation mode
+    outb(PORT + 4, 0x0F);
+
+    DEBUG("serial initialized");
+    return 0;
+}
+
+static int is_transmit_empty()
+{
+    return inb(PORT + 5) & 0x20;
+}
+
+// Serial kernel putchar
+void skputc(char c)
+{
+    while (!is_transmit_empty()); // wait for free spot
+    outb(PORT, c);
+}
+
+// Serial kernel putstring
+void skputs(const char* str)
+{
+    unsigned int i=0;
+    while (str[i])
+    {
+        skputc(str[i]);
+        i++;
+    }
+}

src/io/serial/serial.h

@@ -0,0 +1,11 @@
+#ifndef SERIAL_H
+#define SERIAL_H
+
+void outb(int port, unsigned char data);
+unsigned char inb(int port);
+
+int serial_init();
+void skputs(const char* str);
+void skputc(char c);
+
+#endif

src/io/term.c

@@ -1,105 +0,0 @@
-// Terminal output
-
-#include <limine.h>
-#include <stddef.h>
-#include "kernel.h"
-#include "term.h"
-
-extern struct limine_framebuffer* framebuffer;
-
-// Importing the PSF object file
-extern unsigned char _binary_zap_light16_psf_start[];
-extern unsigned char _binary_zap_light16_psf_end[];
-
-PSF1_Header* font = (PSF1_Header*)_binary_zap_light16_psf_start;
-uint8_t* glyphs = _binary_zap_light16_psf_start + sizeof(PSF1_Header);
-
-#define FONT_WIDTH 8
-#define FONT_HEIGHT font->characterSize
-
-// Character cursor
-typedef struct
-{
-	unsigned int x;
-	unsigned int y;
-} Cursor;
-
-Cursor cursor = {0};
-
-unsigned char* fb;
-
-int term_init()
-{
-	// Get framebuffer address from Limine struct
-	
-	if (framebuffer)
-	{
-		fb = framebuffer->address;
-		return 0;
-	}
-	return -ENOMEM;
-}
-
-// These are marked "static" because we don't wanna expose them all around
-// AKA they should just be seen here (kind of like private functions in cpp)
-static void putpixel(int x, int y, int color)
-{
-	// Depth isn't part of limine_framebuffer attributes so it will be 4
-	unsigned pos = x*4 + y*framebuffer->pitch;
-	fb[pos] = color & 255; // blue channel
-	fb[pos+1] = (color >> 8) & 255; // green
-	fb[pos+2] = (color >> 16) & 255; // blue
-}
-
-static void draw_char(char c, int px, int py, int fg, int bg)
-{
-	uint8_t* glyph = glyphs + ((unsigned char)c * FONT_HEIGHT);
-
-	for (size_t y=0; y<FONT_HEIGHT; y++)
-	{
-		uint8_t row = glyph[y];
-		for (size_t x=0; x<8; x++)
-		{
-			int color = (row & (0x80 >> x)) ? fg : bg;
-			putpixel(px+x, py+y, color);
-		}
-	}
-}
-
-static void putchar(char c)
-{
-	if (c == '\n')
-	{
-		cursor.x = 0;
-		cursor.y++;
-		return;
-	}
-
-	if ((cursor.x+1)*FONT_WIDTH >= framebuffer->width)
-	{
-		cursor.x = 0;
-		cursor.y++;
-	}
-
-	int px = cursor.x * FONT_WIDTH;
-	int py = cursor.y * FONT_HEIGHT;
-	draw_char(c, px, py, WHITE, BLACK);
-	cursor.x++;
-}
-
-// Overhead that could be avoided, right?
-void _putchar(char character)
-{
-	putchar(character);
-}
-
-// Debug-printing
-void kputs(const char* str)
-{
-	unsigned int i=0;
-	while (str[i] != 0)
-	{
-		putchar(str[i]);
-		i++;
-	}
-}

src/io/term/term.c

@@ -0,0 +1,207 @@
+// Terminal output
+/*
+There are a couple of bugs here and there but for now I don't care too much
+because this shitty implementation will be replaced one day by Flanterm
+(once memory management is okay: paging & kernel malloc)
+*/
+
+#include <limine.h>
+#include <stddef.h>
+#include <kernel.h>
+#include "term.h"
+#include "mem/misc/utils.h"
+
+extern struct boot_context boot_ctx;
+
+// Importing the PSF object file
+extern unsigned char _binary_zap_light16_psf_start[];
+extern unsigned char _binary_zap_light16_psf_end[];
+
+PSF1_Header* font = (PSF1_Header*)_binary_zap_light16_psf_start;
+uint8_t* glyphs = _binary_zap_light16_psf_start + sizeof(PSF1_Header);
+
+#define FONT_WIDTH 8
+#define FONT_HEIGHT font->characterSize
+
+// Character cursor
+typedef struct
+{
+	unsigned int x;
+	unsigned int y;
+} Cursor;
+
+Cursor cursor = {0};
+
+unsigned char* fb;
+
+struct limine_framebuffer* framebuffer;
+
+uint8_t lines_length[MAX_LINES];
+
+int term_init()
+{
+	// Get framebuffer address from Limine struct
+	
+	if (boot_ctx.fb)
+	{
+		fb = boot_ctx.fb->address;
+		framebuffer = boot_ctx.fb;
+		DEBUG("terminal initialized, fb=0x%p (width=%u height=%u pitch=%u bpp=%u)", fb, framebuffer->width, framebuffer->height, framebuffer->pitch, framebuffer->bpp);
+		return 0;
+	}
+	return -ENOMEM;
+}
+
+// These are marked "static" because we don't wanna expose them all around
+// AKA they should just be seen here (kind of like private functions in cpp)
+static void putpixel(int x, int y, int color)
+{
+	// Depth isn't part of limine_framebuffer attributes so it will be 4
+	unsigned pos = x*4 + y*framebuffer->pitch;
+	fb[pos] = color & 255; // blue channel
+	fb[pos+1] = (color >> 8) & 255; // green
+	fb[pos+2] = (color >> 16) & 255; // blue
+}
+
+static void draw_char(char c, int px, int py, int fg, int bg)
+{
+	uint8_t* glyph = glyphs + ((unsigned char)c * FONT_HEIGHT);
+
+	for (size_t y=0; y<FONT_HEIGHT; y++)
+	{
+		uint8_t row = glyph[y];
+		for (size_t x=0; x<8; x++)
+		{
+			int color = (row & (0x80 >> x)) ? fg : bg;
+			putpixel(px+x, py+y, color);
+		}
+	}
+}
+
+static void erase_char(int px, int py)
+{
+	for (size_t y=0; y<FONT_HEIGHT; y++)
+	{
+		for (size_t x=0; x<8; x++)
+		{
+			// Black
+			putpixel(px+x, py+y, 0);
+		}
+	}
+}
+
+static inline size_t term_max_lines(void)
+{
+	return framebuffer->height / FONT_HEIGHT;
+}
+
+void term_scroll()
+{
+	const size_t row_height = FONT_HEIGHT;
+	const size_t row_bytes  = framebuffer->pitch;
+	const size_t screen_rows = framebuffer->height;
+
+	// Move framebuffer up by one text row 
+	//memmove(fb, fb + row_height * row_bytes, (screen_rows - row_height) * row_bytes);
+
+	for (size_t i = 0; i < (screen_rows - row_height) * row_bytes; i++)
+	{
+		fb[i] = fb[i + row_height * row_bytes];
+	}
+
+	// Clear last text row
+	size_t clear_start = (screen_rows - row_height) * row_bytes;
+	memset(fb + clear_start, 0, row_height * row_bytes);
+
+	// Shift line lengths by 1 (for backspace handling)
+	size_t max_lines = term_max_lines();
+	for (size_t i = 1; i < max_lines; i++)
+	{
+		lines_length[i - 1] = lines_length[i];
+	}
+
+	lines_length[max_lines - 1] = 0;
+
+	if (cursor.y > 0)
+	{
+		cursor.y--;
+	}
+}
+
+
+void putchar(char c)
+{
+	if ((c == '\n') && ((cursor.y+1)*FONT_HEIGHT >= framebuffer->height))
+	{
+		term_scroll();
+		return;
+	} 
+
+	if (c == '\n')
+	{
+		lines_length[cursor.y] = cursor.x;
+		cursor.x = 0;
+		cursor.y++;
+		return;
+	}
+
+	// TODO: Improperly handled.
+	// When we're on an empty line it should get to the upper line's last character
+	// NOT just the last position possible; we would need to track the last line's character amount for that
+	if (c == '\b')
+	{
+		if (cursor.x == 0 && cursor.y == 0)
+		{
+			// Top-left corner
+			return;
+		}
+
+		if (cursor.x == 0)
+		{
+			cursor.y--;
+			// cursor.x = (framebuffer->width / FONT_WIDTH) -1; // here
+			cursor.x = lines_length[cursor.y];
+		}
+		else {
+			cursor.x--;
+		}
+
+		int px = cursor.x * FONT_WIDTH;
+		int py = cursor.y * FONT_HEIGHT;
+		erase_char(px, py);
+		return;
+	}
+
+	if ((cursor.x+1)*FONT_WIDTH >= framebuffer->width)
+	{
+		cursor.x = 0;
+		cursor.y++;
+	}
+
+	if ((cursor.y+1)*FONT_HEIGHT >= framebuffer->height)
+	{
+		term_scroll();
+	}
+
+	int px = cursor.x * FONT_WIDTH;
+	int py = cursor.y * FONT_HEIGHT;
+	draw_char(c, px, py, WHITE, BLACK);
+	cursor.x++;
+}
+
+// Overhead that could be avoided, right? (for printf)
+void _putchar(char character)
+{
+	putchar(character);
+}
+
+// Debug-printing
+void kputs(const char* str)
+{
+	unsigned int i=0;
+	while (str[i] != 0)
+	{
+		putchar(str[i]);
+		i++;
+	}
+}

src/io/term/term.h

@@ -3,6 +3,7 @@
 
 int term_init();
 void kputs(const char* str);
+void putchar(char c);
 
 enum TermColors
 {
@@ -10,6 +11,8 @@ enum TermColors
     WHITE = 0xffffff
 };
 
+#define MAX_LINES 256
+
 #define PSF1_FONT_MAGIC 0x0436
 
 typedef struct

src/kernel.h

@@ -1,9 +1,39 @@
 #ifndef KERNEL_H
 #define KERNEL_H
 
+#define PEPPEROS_VERSION_MAJOR "0"
+#define PEPPEROS_VERSION_MINOR "0"
+#define PEPPEROS_VERSION_PATCH "1"
+
 enum ErrorCodes
 {
-	ENOMEM
+	ENOMEM,
+	EIO
+};
+
+#define CLEAR_INTERRUPTS __asm__ volatile("cli")
+#define SET_INTERRUPTS __asm__ volatile("sti")
+
+#include "io/serial/serial.h"
+#include "io/term/printf.h"
+#include "idt/idt.h"
+
+#define DEBUG(log, ...) fctprintf((void*)&skputc, 0, "debug: [%s]: " log "\r\n", __FILE__, ##__VA_ARGS__)
+
+#define CHECK_BIT(var,pos) ((var) & (1<<(pos)))
+
+// printf("debug: [%s]: " log "\n", __FILE__, ##__VA_ARGS__);
+
+void panic(struct cpu_status_t* ctx);
+void hcf();
+#define assert(check) do { if(!(check)) hcf(); } while(0)
+
+struct boot_context
+{
+	struct limine_framebuffer* fb;
+	struct limine_memmap_response* mmap;
+	struct limine_hhdm_response* hhdm;
+	struct limine_kernel_address_response* kaddr;
 };
 
 #endif

src/kmain.c

@@ -1,8 +1,19 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <limine.h>
-#include "io/term.h"
-#include "io/printf.h"
+#include "io/term/term.h"
+#include "io/term/printf.h"
+#include "io/serial/serial.h"
+#include "mem/gdt/gdt.h"
+#include "mem/misc/utils.h"
+#include "idt/idt.h"
+#include "kernel.h"
+#include "time/timer.h"
+#include "io/kbd/ps2.h"
+#include "mem/paging/pmm.h"
+#include "mem/paging/paging.h"
+#include "mem/paging/vmm.h"
+#include "mem/heap/kheap.h"
 
 // Limine version used
 __attribute__((used, section(".limine_requests")))
@@ -15,84 +26,35 @@ static volatile struct limine_framebuffer_request framebuffer_request = {
 	.revision = 0
 };
 
+// Memory map request
+__attribute__((used, section(".limine_requests")))
+static volatile struct limine_memmap_request memmap_request = {
+	.id = LIMINE_MEMMAP_REQUEST,
+	.revision = 0
+};
+
+// Higher Half Direct Map
+__attribute__((used, section(".limine_requests")))
+static volatile struct limine_hhdm_request hhdm_request = {
+	.id = LIMINE_HHDM_REQUEST,
+	.revision = 0
+};
+
+// Executable Address/Kernel Address (find base phys/virt address of kernel)
+__attribute__((used, section(".limine_requests")))
+static volatile struct limine_kernel_address_request kerneladdr_request = {
+	.id = LIMINE_KERNEL_ADDRESS_REQUEST,
+	.revision = 0
+};
+
 __attribute__((used, section(".limine_requests_start")))
 static volatile LIMINE_REQUESTS_START_MARKER;
 
 __attribute__((used, section(".limine_requests_end")))
 static volatile LIMINE_REQUESTS_END_MARKER;
 
-struct limine_framebuffer* framebuffer;
-
-// We won't be linked to standard library, but still need the basic mem* functions
-// so everything goes allright with the compiler
-
-// We use the "restrict" keyword on pointers so that the compiler knows it can
-// do more optimization on them (and as it's a much used function, it's good to
-// be able to do that)
-void* memcpy(void* restrict dest, const void* restrict src, size_t n)
-{
-	uint8_t* restrict pdest = (uint8_t* restrict)dest;
-	const uint8_t* restrict psrc = (const uint8_t* restrict)src;
-
-	for (size_t i=0; i<n; i++)
-	{
-		pdest[i] = psrc[i];
-	}
-
-	return dest;
-}
-
-void* memset(void* s, int c, size_t n)
-{
-	uint8_t* p = (uint8_t*)s;
-
-	for (size_t i=0; i<n; i++)
-	{
-		p[i] = (uint8_t)c;
-	}
-
-	return s;
-}
-
-void* memmove(void *dest, const void* src, size_t n)
-{
-	uint8_t* pdest = (uint8_t*)dest;
-	const uint8_t* psrc = (uint8_t*)src;
-
-	if (src > dest)
-	{
-		for (size_t i=0; i<n; i++)
-		{
-			pdest[i] = psrc[i];
-		}
-	} else if (src < dest) 
-	{
-		for (size_t i=n; i>0; i--)
-		{
-			pdest[i-1] = psrc[i-1];
-		}
-	}
-	return dest;	
-}
-
-int memcmp(const void* s1, const void* s2, size_t n)
-{
-	const uint8_t* p1 = (const uint8_t*)s1;
-	const uint8_t* p2 = (const uint8_t*)s2;
-
-	for (size_t i=0; i<n; i++)
-	{
-		if (p1[i] != p2[i])
-		{
-			return p1[i] < p2[i] ? -1 : 1;
-		}
-	}
-
-	return 0;
-}
-
-// Panic 
-static void hcf()
+// Panic (should dump registers etc. in the future)
+void hcf()
 {
 	for (;;)
 	{
@@ -100,19 +62,67 @@ static void hcf()
 	}
 }
 
+void panic(struct cpu_status_t* ctx)
+{
+	DEBUG("\x1b[38;5;231m\x1b[48;5;196mKernel panic!!!\x1b[0m at rip=%p\nSomething went horribly wrong! vect=0x%.2x errcode=0x%x\nrax=%p rbx=%p rcx=%p rdx=%p\nrsi=%p rdi=%p  r8=%p  r9=%p\nr10=%p r11=%p r12=%p r13=%p\nr14=%p r15=%p\n\nflags=%p\nstack at rbp=%p\nHalting...",
+		ctx->iret_rip,
+		ctx->vector_number, ctx->error_code, ctx->rax, ctx->rbx, ctx->rcx, ctx->rdx, ctx->rsi, ctx->rdi,
+		ctx->r8, ctx->r9, ctx->r10, ctx->r11, ctx->r12, ctx->r13, ctx->r14, ctx->r15, ctx->iret_flags,
+		ctx->rbp);
+	hcf();
+}
+
+const char* splash = "pepperOS version "PEPPEROS_VERSION_MAJOR"."PEPPEROS_VERSION_MINOR"."PEPPEROS_VERSION_PATCH"\n";
+
+struct boot_context boot_ctx;
+
 // This is our entry point
 void kmain()
 {
 	if (!LIMINE_BASE_REVISION_SUPPORTED) hcf();
-	if (framebuffer_request.response == NULL || framebuffer_request.response->framebuffer_count < 1) hcf();
 
-	// Get the first framebuffer from the response
-	framebuffer = framebuffer_request.response->framebuffers[0];
+	// Populate boot context
+ 	boot_ctx.fb = framebuffer_request.response ? framebuffer_request.response->framebuffers[0] : NULL;
+	boot_ctx.mmap = memmap_request.response ? memmap_request.response : NULL;
+	boot_ctx.hhdm = hhdm_request.response ? hhdm_request.response : NULL;
+	boot_ctx.kaddr = kerneladdr_request.response ? kerneladdr_request.response : NULL;
 
-	if (term_init()) hcf();
+	serial_init();
 
-	// Draw something
-	printf("%s, %s!", "Hello", "world");
+	memmap_display(boot_ctx.mmap);
+	hhdm_display(boot_ctx.hhdm);
+	DEBUG("kernel: phys_base=0x%p virt_base=0x%p", boot_ctx.kaddr->physical_base, boot_ctx.kaddr->virtual_base);
+
+	CLEAR_INTERRUPTS;
+	gdt_init();
+	idt_init();
+	timer_init();
+	SET_INTERRUPTS;
+
+	pmm_init(boot_ctx.mmap, boot_ctx.hhdm);
+
+	// Remap kernel , HHDM and framebuffer
+	paging_init(boot_ctx.kaddr, boot_ctx.fb);
+	
+	kheap_init();
+
+	void* ptr = kmalloc(10); DEBUG("(KMALLOC TEST) Allocated 10 bytes at 0x%p", ptr);
+	void* ptr2 = kmalloc(200); DEBUG("(KMALLOC TEST) Allocated 200 bytes at 0x%p", ptr2);
+	kfree(ptr);
+	void* ptr3 = kmalloc(5); DEBUG("(KMALLOC TEST) Allocated 5 bytes at 0x%p", ptr3);
+
+	vmm_init();
+
+	keyboard_init(FR);
+
+	term_init();
+	kputs(splash);
+
+	for (int i=0; i<50; i++)
+	{
+		printf("testing, attention please %d\n", i);
+		timer_wait(1000);
+	}
 
 	hcf();
 }

src/mem/gdt/gdt.c

@@ -0,0 +1,83 @@
+#include "gdt.h"
+#include <stdint.h>
+#include "io/serial/serial.h"
+#include <kernel.h>
+
+// Descriptors are 8-byte wide (64bits)
+// So the selectors will be (in bytes): 0x0, 0x8, 0x10, 0x18, etc..
+uint64_t gdt_entries[NUM_GDT_ENTRIES];
+struct GDTR gdtr;
+
+static void gdt_load()
+{
+    asm("lgdt %0" : : "m"(gdtr));
+}
+
+static void gdt_flush()
+{
+    // Here, 0x8 is the kernel code selector
+    // and 0x10 is the kernel data selector
+    asm volatile (
+        "mov $0x10, %%ax \n" // Reload segments with kernel data selector
+        "mov %%ax, %%ds \n"
+        "mov %%ax, %%es \n"
+        "mov %%ax, %%fs \n"
+        "mov %%ax, %%gs \n"
+        "mov %%ax, %%ss \n"
+
+        "pushq $0x8      \n"   // CS reload
+        "lea 1f(%%rip), %%rax \n"
+        "push %%rax     \n"
+        "lretq          \n"
+        "1:             \n" // Execution continues here after CS reload
+        :
+        :
+        : "rax", "memory"
+    );
+}
+
+void gdt_init()
+{
+    // Null descriptor (required)
+    gdt_entries[0] = 0;
+
+    // Kernel code segment
+    uint64_t kernel_code = 0;
+    kernel_code |= 0b1101 << 8; // Selector type: accessed, read-enable, no conforming
+    kernel_code |= 1 << 12; // not a system descriptor
+    kernel_code |= 0 << 13; // DPL field = 0
+    kernel_code |= 1 << 15; // Present
+    kernel_code |= 1 << 21; // Long mode
+
+    // Left shift 32 bits so we place our stuff in the upper 32 bits of the descriptor.
+    // The lower 32 bits contain limit and part of base and therefore are ignored in Long Mode
+    // (because we'll use paging; segmentation is used only for legacy)
+    gdt_entries[1] = kernel_code << 32;
+
+    uint64_t kernel_data = 0;
+    kernel_data |= 0b0011 << 8;
+    kernel_data |= 1 << 12;
+    kernel_data |= 0 << 13;
+    kernel_data |= 1 << 15;
+    kernel_data |= 1 << 21;
+
+    gdt_entries[2] = kernel_data << 32;
+
+    // We re-use the kernel descriptors here, and just update their DPL fields
+    // (Descriptor privilege level) from ring 0 -> to ring 3 (userspace)
+    uint64_t user_code = kernel_code | (3 << 13);
+    gdt_entries[3] = user_code;
+
+    uint64_t user_data = kernel_data | (3 << 13);
+    gdt_entries[4] = user_data;
+
+    // The -1 subtraction is some wizardry explained in the OSDev wiki -> GDT
+    gdtr.limit = NUM_GDT_ENTRIES * sizeof(uint64_t) - 1;
+    gdtr.address = (uint64_t)gdt_entries;
+
+    // Load the GDT we created, flush the old one
+    gdt_load();
+    gdt_flush();
+
+    DEBUG("GDT initialized");
+}

src/mem/gdt/gdt.h

@@ -0,0 +1,26 @@
+#ifndef GDT_H
+#define GDT_H
+
+#include <stdint.h>
+
+// We're using the GDT for segmentation, but as we want to target Long Mode,
+// we'll only use this as a requirement for paging, not more.
+// This means base 0 and no limit (whole address space)
+
+#define NUM_GDT_ENTRIES 5
+
+#define NULL_SELECTOR 0x00
+#define KERNEL_CODE_SEGMENT 0x08
+#define KERNEL_DATA_SEGMENT 0x10
+#define USER_CODE_SEGMENT 0x18
+#define USER_DATA_SEGMENT 0x20
+
+struct GDTR 
+{
+    uint16_t limit;
+    uint64_t address;
+} __attribute__((packed));
+
+void gdt_init();
+
+#endif

src/mem/heap/kheap.c

@@ -0,0 +1,106 @@
+#include "kheap.h"
+#include "mem/paging/paging.h"
+#include "mem/paging/pmm.h"
+#include <stddef.h>
+#include <kernel.h>
+
+extern uint64_t kernel_phys_base;
+extern uint64_t kernel_virt_base;
+
+uintptr_t kheap_start;
+
+static struct heap_block_t* head = NULL;
+static uintptr_t end;
+
+// Kernel root table (level 4)
+extern uint64_t *kernel_pml4;
+
+static void kheap_map_page()
+{
+    uintptr_t phys = pmm_alloc();
+    paging_map_page(kernel_pml4, end, phys, PTE_PRESENT | PTE_WRITABLE | PTE_NOEXEC);
+    end += PAGE_SIZE;
+    DEBUG("Mapped first kheap page");
+}
+
+void kheap_init()
+{
+    kheap_start = ALIGN_UP(kernel_virt_base + KERNEL_SIZE, PAGE_SIZE);
+    end = kheap_start;
+
+    // At least 1 page must be mapped for it to work
+    kheap_map_page();
+
+    // Give linked list head its properties
+    head = (struct heap_block_t*)kheap_start;
+    head->size = PAGE_SIZE - sizeof(struct heap_block_t);
+    head->free = true;
+    head->next = NULL;
+    DEBUG("kheap initialized, head=0x%p, size=%u", head, head->size);
+}
+
+void* kmalloc(size_t size)
+{
+    // No size, no memory allocated!
+    if (!size) return NULL;
+
+    struct heap_block_t* curr = head;
+
+    while (curr)
+    {
+        // Is block free and big enough for us?
+        if (curr->free && curr->size >= size)
+        {
+            // We split the block if it is big enough
+            if (curr->size > size + sizeof(struct heap_block_t))
+            {
+                struct heap_block_t* new_block = (struct heap_block_t*)((uintptr_t)curr + sizeof(struct heap_block_t) + size);
+                // We have to subtract the size of our block struct
+                new_block->size = curr->size - size - sizeof(struct heap_block_t);
+                new_block->free = true;
+
+                // Then we chain up the block in the list
+                new_block->next = curr->next;
+                curr->next = new_block;
+
+                curr->size = size;
+            }
+
+            // Found a good block, we return it
+            curr->free = false;
+            return (void*)((uintptr_t)curr + sizeof(struct heap_block_t));
+        }
+        // Continue browsing the list if nothing good was found yet
+        curr = curr->next;
+    }
+
+    // If we're hear it means we didn't have enough memory
+    // for the block allocation. So we will allocate more..
+    uintptr_t old_end = end;
+    kheap_map_page();
+
+    struct heap_block_t* block = (struct heap_block_t*)old_end;
+    block->size = PAGE_SIZE - sizeof(struct heap_block_t);
+    block->free = false;
+    block->next = NULL;
+
+    // Put the block at the end of the list
+    curr = head;
+    while (curr->next)
+    {
+        curr = curr->next;
+    }
+    curr->next = block;
+
+    return (void*)((uintptr_t)block + sizeof(struct heap_block_t));
+}
+
+void kfree(void* ptr)
+{
+    // Nothing to free
+    if (!ptr) return;
+
+    // Set it free!
+    struct heap_block_t* block = (struct heap_block_t*)((uintptr_t)ptr - sizeof(struct heap_block_t));
+    block->free = true;
+}

src/mem/heap/kheap.h

@@ -0,0 +1,26 @@
+#ifndef KHEAP_H
+#define KHEAP_H
+
+// We need some kind of simple kernel heap to make our linked list
+// for the VMM, as we need "malloc" and "free" for that data structure.
+// When the kernel heap is ready, we can alloc our VM object linked list
+// and then continue working on the VMM.
+
+// 16MB should be enough for some linked lists
+#define KHEAP_SIZE (16*1024*1024)
+
+#include <stdbool.h>
+#include <stddef.h>
+
+struct heap_block_t
+{
+    size_t size;
+    bool free;
+    struct heap_block_t* next;
+};
+
+void kheap_init();
+void* kmalloc(size_t size);
+void kfree(void* ptr);
+
+#endif

src/mem/misc/utils.c

@@ -0,0 +1,122 @@
+#include <stddef.h>
+#include <stdint.h>
+#include <limine.h>
+#include "kernel.h"
+#include "string/string.h"
+
+// We won't be linked to standard library, but still need the basic mem* functions
+// so everything goes allright with the compiler
+
+// We use the "restrict" keyword on pointers so that the compiler knows it can
+// do more optimization on them (and as it's a much used function, it's good to
+// be able to do that)
+void* memcpy(void* restrict dest, const void* restrict src, size_t n)
+{
+	uint8_t* restrict pdest = (uint8_t* restrict)dest;
+	const uint8_t* restrict psrc = (const uint8_t* restrict)src;
+
+	for (size_t i=0; i<n; i++)
+	{
+		pdest[i] = psrc[i];
+	}
+
+	return dest;
+}
+
+void* memset(void* s, int c, size_t n)
+{
+	uint8_t* p = (uint8_t*)s;
+
+	for (size_t i=0; i<n; i++)
+	{
+		p[i] = (uint8_t)c;
+	}
+
+	return s;
+}
+
+void* memmove(void *dest, const void* src, size_t n)
+{
+	uint8_t* pdest = (uint8_t*)dest;
+	const uint8_t* psrc = (uint8_t*)src;
+
+	if (src > dest)
+	{
+		for (size_t i=0; i<n; i++)
+		{
+			pdest[i] = psrc[i];
+		}
+	} else if (src < dest) 
+	{
+		for (size_t i=n; i>0; i--)
+		{
+			pdest[i-1] = psrc[i-1];
+		}
+	}
+	return dest;	
+}
+
+int memcmp(const void* s1, const void* s2, size_t n)
+{
+	const uint8_t* p1 = (const uint8_t*)s1;
+	const uint8_t* p2 = (const uint8_t*)s2;
+
+	for (size_t i=0; i<n; i++)
+	{
+		if (p1[i] != p2[i])
+		{
+			return p1[i] < p2[i] ? -1 : 1;
+		}
+	}
+
+	return 0;
+}
+
+// Display the memmap so we see how the memory is laid out at handoff
+void memmap_display(struct limine_memmap_response* response)
+{
+	DEBUG("Got memory map from Limine: revision %u, %u entries", response->revision, response->entry_count);
+
+	for (size_t i=0; i<response->entry_count; i++)
+	{
+		struct limine_memmap_entry* entry = response->entries[i];
+		char type[32] = {0};
+		switch(entry->type)
+		{
+			case LIMINE_MEMMAP_USABLE:
+				strcpy(type, "USABLE");
+				break;
+			case LIMINE_MEMMAP_RESERVED:
+				strcpy(type, "RESERVED");
+				break;
+			case LIMINE_MEMMAP_ACPI_RECLAIMABLE:
+				strcpy(type, "ACPI_RECLAIMABLE");
+				break;
+			case LIMINE_MEMMAP_ACPI_NVS:
+				strcpy(type, "ACPI_NVS");
+				break;
+			case LIMINE_MEMMAP_BAD_MEMORY:
+				strcpy(type, "BAD_MEMORY");
+				break;
+			case LIMINE_MEMMAP_BOOTLOADER_RECLAIMABLE:
+				strcpy(type, "BOOTLOADER_RECLAIMABLE");
+				break;
+			case LIMINE_MEMMAP_KERNEL_AND_MODULES:
+				strcpy(type, "KERNEL_AND_MODULES");
+				break;
+			case LIMINE_MEMMAP_FRAMEBUFFER:
+				strcpy(type, "FRAMEBUFFER");
+				break;
+			default:
+				strcpy(type, "UNKNOWN");
+				break;
+		}
+		DEBUG("entry %02u: [0x%016x | %016u bytes] - %s", i, entry->base, entry->length, type);
+	}
+}
+
+// Display the HHDM
+void hhdm_display(struct limine_hhdm_response* hhdm)
+{
+	DEBUG("Got HHDM revision=%u offset=0x%p", hhdm->revision, hhdm->offset);
+}

src/mem/misc/utils.h

@@ -0,0 +1,14 @@
+#ifndef MEM_UTILS_H
+#define MEM_UTILS_H
+
+#include <stddef.h>
+
+void* memcpy(void* restrict dest, const void* restrict src, size_t n);
+void* memset(void* s, int c, size_t n);
+void* memmove(void *dest, const void* src, size_t n);
+int memcmp(const void* s1, const void* s2, size_t n);
+
+void memmap_display(struct limine_memmap_response* response);
+void hhdm_display(struct limine_hhdm_response* hhdm);
+
+#endif

src/mem/paging/paging.c

@@ -0,0 +1,159 @@
+#include "paging.h"
+#include "pmm.h"
+#include <kernel.h>
+#include <stddef.h>
+#include <limine.h>
+
+/*
+Paging on x86 uses four different page table levels:
+cr3 register contains the phys address for the PML4 (root directory)
+
+Each directory/table is made of 512 entries, each one uint64_t
+Each of these entries have special bits (PRESENT/WRITEABLE/USER/etc.)
+that dictates their attributes. Also these bits fall back on children tables.
+
+If we use 1GB huge pages: PML4 -> PDPT -> 1gb pages
+2MB huge pages: PML4 -> PDPT -> PD -> 2mb pages
+4KB (regular size): PML4 -> PDPT -> PD -> PT -> 4kb pages
+*/
+
+static inline void load_cr3(uint64_t value) {
+    asm volatile ("mov %0, %%cr3" :: "r"(value) : "memory");
+}
+
+// To flush TLB
+static inline void invlpg(void *addr)
+{
+    asm volatile("invlpg (%0)" :: "r"(addr) : "memory");
+}
+
+// Allocates a 512-entry 64bit page table/directory/whatever (zeroed)
+static uint64_t* alloc_page_table()
+{
+    uint64_t* virt = (uint64_t*)PHYS_TO_VIRT(pmm_alloc());
+
+    for (size_t i=0; i<512; i++)
+    {
+        virt[i] = 0;
+    }
+    return virt;
+}
+
+// Kernel paging root table, that will be placed in cr3
+__attribute__((aligned(4096)))
+uint64_t *kernel_pml4;
+
+// Map a page, taking virt and phys address. This will go through the paging structures
+// beginning at the given root table, translate the virtual address in indexes in
+// page table/directories, and then mapping the correct page table entry with the
+// given physical address + flags
+void paging_map_page(uint64_t* root_table, uint64_t virt, uint64_t phys, uint64_t flags)
+{
+    virt = PAGE_ALIGN_DOWN(virt);
+    phys = PAGE_ALIGN_DOWN(phys);
+
+    // Translate the virt address into page table indexes
+    uint64_t pml4_i = PML4_INDEX(virt);
+    uint64_t pdpt_i = PDPT_INDEX(virt);
+    uint64_t pd_i = PD_INDEX(virt);
+    uint64_t pt_i = PT_INDEX(virt);
+
+    uint64_t *pdpt, *pd, *pt;
+
+    // PML4
+    // If the entry at index is not present, allocate enough space for it
+    // then populate the entry with correct addr + flags
+    if (!(root_table[pml4_i] & PTE_PRESENT))
+    {
+        pdpt = alloc_page_table();
+        root_table[pml4_i] = VIRT_TO_PHYS(pdpt) | PTE_PRESENT | PTE_WRITABLE;
+    }
+    else {
+        pdpt = (uint64_t *)PHYS_TO_VIRT(root_table[pml4_i] & ~0xFFFULL);
+    }
+
+    // PDPT: same here
+    if (!(pdpt[pdpt_i] & PTE_PRESENT))
+    {
+        pd = alloc_page_table();
+        pdpt[pdpt_i] = VIRT_TO_PHYS(pd) | PTE_PRESENT | PTE_WRITABLE;
+    } 
+    else {
+        pd = (uint64_t *)PHYS_TO_VIRT(pdpt[pdpt_i] & ~0xFFFULL);
+    }
+
+    // PD: and here
+    if (!(pd[pd_i] & PTE_PRESENT))
+    {
+        pt = alloc_page_table();
+        pd[pd_i] = VIRT_TO_PHYS(pt) | PTE_PRESENT | PTE_WRITABLE;
+    }
+    else {
+        pt = (uint64_t *)PHYS_TO_VIRT(pd[pd_i] & ~0xFFFULL);
+    }
+
+    // PT: finally, populate the page table entry
+    pt[pt_i] = phys | flags | PTE_PRESENT;
+
+    // Flush TLB (apply changes)
+    invlpg((void *)virt);
+}
+
+uint64_t kernel_phys_base;
+uint64_t kernel_virt_base;
+
+void paging_init(struct limine_kernel_address_response* kaddr, struct limine_framebuffer* fb)
+{
+    // We should map the kernel, GDT, IDT, stack, framebuffer.
+    // Optionally we could map ACPI tables (we can find them in the Limine memmap)
+
+    kernel_phys_base = kaddr->physical_base;
+    kernel_virt_base = kaddr->virtual_base;
+
+    DEBUG("Kernel lives at virt=0x%p phys=0x%p", kernel_virt_base, kernel_phys_base);
+
+    kernel_pml4 = alloc_page_table();
+
+    // for debug
+    uint64_t page_count = 0;
+
+    // HHDM map first 1 GB using given offset
+    for (uint64_t i=0; i<0x40000000; i += PAGE_SIZE)
+    {
+        //paging_kmap_page(i+hhdm_off, i, PTE_WRITABLE);
+        paging_map_page(kernel_pml4, i+hhdm_off, i, PTE_WRITABLE);
+        page_count++;
+    }
+    DEBUG("Mapped %u pages for first 1GB (HHDM)", page_count); page_count = 0;
+
+    // Map the kernel (according to virt/phys_base given by Limine)
+    // SOME DAY when we want a safer kernel we should map .text as Read/Exec
+    // .rodata as Read and .data as Read/Write
+    // For now who gives a shit, let's RWX all kernel
+    for (uint64_t i = 0; i < KERNEL_SIZE; i += PAGE_SIZE)
+    {
+        //paging_kmap_page(kernel_virt_base+i, kernel_phys_base+i, PTE_WRITABLE);
+        paging_map_page(kernel_pml4, kernel_virt_base+i, kernel_phys_base+i, PTE_WRITABLE);
+        page_count++;
+    }
+    DEBUG("Mapped %u pages for kernel", page_count); page_count = 0;
+
+    // Get the framebuffer phys/virt address, and size
+    uint64_t fb_virt = (uint64_t)fb->address;
+    uint64_t fb_phys = VIRT_TO_PHYS(fb_virt);
+    uint64_t fb_size = fb->pitch * fb->height;
+    uint64_t fb_pages = (fb_size + PAGE_SIZE-1)/PAGE_SIZE;
+
+    // Map the framebuffer (with cache-disable & write-through)
+    for (uint64_t i=0; i<fb_pages; i++)
+    {
+        //paging_kmap_page(fb_virt+i*PAGE_SIZE, fb_phys+i*PAGE_SIZE, PTE_WRITABLE | PTE_PCD | PTE_PWT);
+        paging_map_page(kernel_pml4, fb_virt+i*PAGE_SIZE, fb_phys+i*PAGE_SIZE, PTE_WRITABLE | PTE_PCD | PTE_PWT);
+        page_count++;
+    }
+    DEBUG("Mapped %u pages for framebuffer", page_count);
+
+    // Finally, we load the physical address of our PML4 (root table) into cr3
+    load_cr3(VIRT_TO_PHYS(kernel_pml4));
+    DEBUG("cr3 loaded, we're still alive");
+}

src/mem/paging/paging.h

@@ -0,0 +1,44 @@
+#ifndef PAGING_H
+#define PAGING_H
+
+#define PAGE_SIZE 4096
+#define BITS_PER_ROW 64
+
+#include <stdint.h>
+#include <limine.h>
+
+void paging_init(struct limine_kernel_address_response* kaddr, struct limine_framebuffer* fb);
+void paging_map_page(uint64_t* root_table, uint64_t virt, uint64_t phys, uint64_t flags);
+
+extern uint64_t hhdm_off;
+
+#define PHYS_TO_VIRT(x) ((void*)((uintptr_t)(x) + hhdm_off))
+#define VIRT_TO_PHYS(x) ((uintptr_t)(x) - hhdm_off)
+
+// Stole it
+#define ALIGN_UP(x, align)   (((x) + ((align) - 1)) & ~((align) - 1))
+#define ALIGN_DOWN(x, align) ((x) & ~((align) - 1))
+#define PAGE_ALIGN_DOWN(x) ((x) & ~0xFFFULL)
+
+#define PML4_INDEX(x) (((x) >> 39) & 0x1FF)
+#define PDPT_INDEX(x) (((x) >> 30) & 0x1FF)
+#define PD_INDEX(x)   (((x) >> 21) & 0x1FF)
+#define PT_INDEX(x)   (((x) >> 12) & 0x1FF)
+
+// Page entry special bits
+// Bits set on a parent (directory, table) fall back to their children
+#define PTE_PRESENT     (1ULL << 0)
+#define PTE_WRITABLE    (1ULL << 1)
+#define PTE_USER        (1ULL << 2)
+#define PTE_PWT         (1ULL << 3)
+#define PTE_PCD         (1ULL << 4)
+#define PTE_HUGE        (1ULL << 7)
+#define PTE_NOEXEC      (1ULL << 63)
+
+// Specified in linker.ld
+#define KERNEL_BASE 0xFFFFFFFF80000000ULL
+
+// 2 MB should be enough (as of now, the whole kernel ELF is around 75kb)
+#define KERNEL_SIZE 0x200000
+
+#endif

src/mem/paging/pmm.c

@@ -0,0 +1,103 @@
+// OMG here we are. I'm cooked.
+
+/*
+pmm - Physical Memory Manager
+will manage 4kb pages physically
+it will probably need to get some info from Limine,
+to see which pages are used by kernel/bootloader/mmio/fb etc.
+*/
+
+#include "paging.h"
+#include <limine.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <kernel.h>
+#include "mem/misc/utils.h"
+#include "pmm.h"
+
+/*
+First we'll have to discover the physical memory layout,
+and for that we can use a Limine request.
+*/
+
+/*
+We will look for the biggest usable physical memory region
+and use this for the bitmap. The reserved memory will be ignored.
+*/
+
+struct limine_memmap_entry* biggest_entry;
+
+static void pmm_find_biggest_usable_region(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm)
+{
+    // Max length of a usable memory region
+    uint64_t length_max = 0;
+    uint64_t offset = hhdm->offset;
+
+    DEBUG("Usable Memory:");
+    for (size_t i=0; i<memmap->entry_count; i++)
+    {
+        struct limine_memmap_entry* entry = memmap->entries[i];
+
+        if (entry->type == LIMINE_MEMMAP_USABLE)
+        {
+            DEBUG("0x%p-0x%p mapped at 0x%p-0x%p", entry->base, entry->base+entry->length,
+                        entry->base+offset, entry->base+entry->length+offset);
+            if (entry->length > length_max)
+            {
+                length_max = entry->length;
+                biggest_entry = entry;
+            }
+        }
+    }
+
+    DEBUG("Biggest usable memory region:");
+    DEBUG("0x%p-0x%p mapped at 0x%p-0x%p", biggest_entry->base, biggest_entry->base + biggest_entry->length,
+            biggest_entry->base+offset, biggest_entry->base+biggest_entry->length+offset);
+}
+
+// Offset from Higher Half Direct Map
+uint64_t hhdm_off;
+
+static uintptr_t g_freelist = 0;
+
+uintptr_t pmm_alloc()
+{
+    if (!g_freelist) return 0;
+    uintptr_t addr = g_freelist;
+    g_freelist = *(uintptr_t*) PHYS_TO_VIRT(g_freelist);
+    return addr;
+}
+
+void pmm_free(uintptr_t addr)
+{
+    *(uintptr_t*) PHYS_TO_VIRT(addr) = g_freelist;
+    g_freelist = addr;
+}
+
+static void pmm_init_freelist()
+{
+    // We simply call pmm_free() on each page that is marked USABLE
+    // in our big memory region.
+    uint64_t base = ALIGN_UP(biggest_entry->base, PAGE_SIZE);
+    uint64_t end = ALIGN_DOWN(biggest_entry->base + biggest_entry->length, PAGE_SIZE);
+
+    uint64_t page_count=0;
+    for (uint64_t addr = base; addr < end; addr += PAGE_SIZE)
+    {
+        pmm_free(addr);
+        //DEBUG("page %u lives at phys 0x%p (virt 0x%p)", page_count, addr, PHYS_TO_VIRT(addr));
+        page_count++;
+    }
+    DEBUG("%u frames in freelist, available for use (%u bytes)", page_count, page_count*PAGE_SIZE);
+}
+
+void pmm_init(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm)
+{
+    hhdm_off = hhdm->offset;
+    pmm_find_biggest_usable_region(memmap, hhdm);
+    //pmm_allocate_bitmap(hhdm); too complicated for my small brain
+    
+    // Now we have biggest USABLE region,
+    // so to populate the free list we just iterate through it
+    pmm_init_freelist();
+}

src/mem/paging/pmm.h

@@ -0,0 +1,10 @@
+#ifndef PAGING_PMM_H
+#define PAGING_PMM_H
+
+#include <limine.h>
+
+void pmm_init(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm);
+void pmm_free(uintptr_t addr);
+uintptr_t pmm_alloc();
+
+#endif

src/mem/paging/vmm.c

@@ -0,0 +1,66 @@
+/*
+The VMM (virtual memory manager) will have two roles:
+- mapping pages
+- unmapping pages
+in a specified virtual space
+
+compared to the PMM which allocs/frees 4kb frames ("physical pages").
+*/
+
+#include "vmm.h"
+#include "paging.h"
+#include <stddef.h>
+#include "pmm.h"
+#include <kernel.h>
+
+void* vmm_pt_root = 0;
+
+// Linked list head for virtual memory objects
+struct vm_object* vm_objs = NULL;
+
+
+uint64_t convert_x86_vm_flags(size_t flags)
+{
+    uint64_t value = 0;
+    if (flags & VM_FLAG_WRITE)
+    {
+        value |= PTE_WRITABLE;
+    }
+    if (flags & VM_FLAG_USER)
+    {
+        value |= PTE_USER;
+    }
+    if ((flags & VM_FLAG_EXEC) == 0)
+    {
+        value |= PTE_NOEXEC;
+    }
+    return value;
+}
+
+extern uint64_t *kernel_pml4;
+
+void vmm_setup_pt_root()
+{
+    // We alloc a physical page (frame) for the pointer, then map it
+    // to virt (pointer)
+    uintptr_t phys = pmm_alloc();
+    vmm_pt_root = (void*)kernel_pml4;
+    paging_map_page(kernel_pml4, (uint64_t)vmm_pt_root, phys, convert_x86_vm_flags(VM_FLAG_WRITE | VM_FLAG_EXEC));
+    DEBUG("VMM setup: vmm_pt_root=0x%p (phys=0x%p)", vmm_pt_root, phys);
+}
+
+/* void* vmm_alloc(size_t length, size_t flags)
+{
+    // We will try to allocate at least length bytes, which have to be rounded UP to
+    // the next page so its coherent with the PMM
+    size_t len = ALIGN_UP(length, PAGE_SIZE);
+
+    // Need to implement this (as linked list)
+    // but for now kernel heap is sufficient
+    // The VMM will prob be more useful when we have userspace
+} */
+
+void vmm_init()
+{
+    vmm_setup_pt_root();
+}

src/mem/paging/vmm.h

@@ -0,0 +1,29 @@
+#ifndef VMM_H
+#define VMM_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+/*
+This will be our linked list of virtual memory objects.
+Flags here aren't x86 flags, they are platform-agnostic
+kernel-defined flags.
+*/
+
+struct vm_object
+{
+    uintptr_t base;
+    size_t length;
+    size_t flags;
+    struct vm_object* next;
+};
+
+// Flags bitfield
+#define VM_FLAG_NONE 0
+#define VM_FLAG_WRITE (1 << 0)
+#define VM_FLAG_EXEC (1 << 1)
+#define VM_FLAG_USER (1 << 2)
+
+void vmm_init();
+
+#endif

src/string/string.c

@@ -0,0 +1,6 @@
+char* strcpy(char *dest, const char *src)
+{
+    char *temp = dest;
+    while((*dest++ = *src++));
+    return temp;
+}

src/string/string.h

@@ -0,0 +1,6 @@
+#ifndef STRING_H
+#define STRING_H
+
+char *strcpy(char *dest, const char *src);
+
+#endif

src/time/timer.c

@@ -0,0 +1,88 @@
+#include <stdint.h>
+#include "io/serial/serial.h"
+#include <kernel.h>
+
+/*
+For now, the timer module will be using the PIC.
+Even though it's quite old, it's still supported by newer CPUs
+and it will be precise enough for what we'll do. Also it's easier
+to implement than ACPI etc. (we may upgrade to ACPI when we're
+interested in multi-core functionnality like SMP)
+*/
+
+volatile uint64_t ticks = 0;
+
+void pic_remap()
+{
+    uint8_t master_mask = inb(0x21);
+    uint8_t slave_mask  = inb(0xA1);
+
+    // ICW1: start initialization
+    outb(0x20, 0x11);
+    outb(0xA0, 0x11);
+
+    // ICW2: vector offsets
+    outb(0x21, 0x20); // Master PIC -> 0x20
+    outb(0xA1, 0x28); // Slave PIC  -> 0x28
+
+    // ICW3: tell Master about Slave at IRQ2 (0000 0100)
+    outb(0x21, 0x04);
+    // ICW3: tell Slave its cascade identity (0000 0010)
+    outb(0xA1, 0x02);
+
+    // ICW4: 8086 mode
+    outb(0x21, 0x01);
+    outb(0xA1, 0x01);
+
+    // Restore saved masks
+    outb(0x21, master_mask);
+    outb(0xA1, slave_mask);
+}
+
+void pic_enable()
+{
+    // Enabling IRQ0 (unmasking it) but not the others
+    uint8_t mask = inb(0x21);
+    mask &= ~(1 << 0);  // Set IRQ0 (timer, clear bit 0)
+    mask &= ~(1 << 1); // Set IRQ1 (PS/2 Keyboard, clear bit 1)
+    outb(0x21, mask);
+}
+
+/*
+Base frequency = 1.193182 MHz
+1 tick per ms (divide by 1000) = roughly 1193 Hz
+*/
+void pit_init()
+{
+    uint32_t frequency = 1000; // 1 kHz
+    uint32_t divisor = 1193182 / frequency;
+
+    // Set PIT to mode 3, channel 0
+    outb(0x43, 0x36); // 0x36
+
+    // Send divisor (low byte, then high byte)
+    outb(0x40, divisor & 0xFF);
+    outb(0x40, (divisor >> 8) & 0xFF);
+}
+
+// Wait n ticks
+// Given that there's a tick every 1ms, wait n milliseconds
+void timer_wait(uint64_t wait_ticks)
+{
+    uint64_t then = ticks + wait_ticks;
+    while (ticks < then)
+    {
+        asm("hlt");
+    };
+}
+
+void timer_init()
+{
+    // Remapping the PIC, because at startup it conflicts with
+    // the reserved IRQs we have for faults/exceptions etc.
+    // so we move its IRQ0 to something not reserved (32)
+    pic_remap();
+    pic_enable();
+    pit_init();
+    DEBUG("PIT initialized");
+}

src/time/timer.h

@@ -0,0 +1,7 @@
+#ifndef TIMER_H
+#define TIMER_H
+
+void timer_init();
+void timer_wait(unsigned int wait_ticks);
+
+#endif