From 09cbd7a78f3a839ed93a00892f28410243c2d2f1 Mon Sep 17 00:00:00 2001
From: Freywar Ulvnaudgari <freywar.ulvnaudgari@neuroeventlabs.com>
Date: Mon, 8 Jun 2026 19:17:27 +0300
Subject: [PATCH] Start isolating processes

Kernel moved to a fixed range high in address space. Memory allocation
now happens per process. Single kernel process added.
---
 src/app/cat.c      | 12 ++++-----
 src/app/ls.c       | 12 ++++-----
 src/app/terminal.c |  8 +++---
 src/bootloader.asm | 21 ++++++++++------
 src/fat16.c        | 61 +++++++++++++++++++++++-----------------------
 src/fat16.h        | 16 ++++++------
 src/fs.c           | 29 +++++++++++-----------
 src/fs.h           | 16 ++++++------
 src/kernel.c       | 16 ++++++------
 src/linker.ld      |  2 +-
 src/memory.c       | 38 ++++++++++++++---------------
 src/memory.h       | 13 +++++++---
 src/path.c         | 23 +++++++++--------
 src/path.h         |  7 +++---
 src/process.h      | 11 ++++++---
 src/string.c       | 39 ++++++++++++++---------------
 src/string.h       |  2 +-
 src/vga.c          |  3 +--
 18 files changed, 173 insertions(+), 156 deletions(-)

diff --git a/src/app/cat.c b/src/app/cat.c
index 35e293f..afa84da 100644
--- a/src/app/cat.c
+++ b/src/app/cat.c
@@ -10,7 +10,7 @@ void cat(process_t *proc, uint8_t argc, char **argv) {
     return;
   }
 
-  path_t *path = path_open(proc->root, proc->cwd, argv[1]);
+  path_t *path = path_open(proc, proc->cwd, argv[1]);
   if (!path) {
     WRITE_S("cat: invalid path\n");
     return;
@@ -19,13 +19,13 @@ void cat(process_t *proc, uint8_t argc, char **argv) {
   fs_node_t *curr = path->depth ? path->stack[path->depth - 1] : proc->root;
   if (curr->is_dir) {
     WRITE_S("cat: can not print a directory\n");
-    path_close(path);
+    path_close(proc, path);
     return;
   }
 
-  char *content = memory_allocate(curr->size + 1);
-  fs_read(curr, 0, curr->size, content);
+  char *content = memory_allocate(proc, curr->size + 1);
+  fs_read(proc, curr, 0, curr->size, content);
   proc->stdout->write(proc->stdout, content, curr->size);
-  memory_free(content);
-  path_close(path);
+  memory_free(proc, content);
+  path_close(proc, path);
 }
diff --git a/src/app/ls.c b/src/app/ls.c
index 05a1990..b7f3cca 100644
--- a/src/app/ls.c
+++ b/src/app/ls.c
@@ -9,7 +9,7 @@ void ls(process_t *proc, uint8_t argc, char **argv) {
     return;
   }
 
-  path_t *path = path_open(proc->root, proc->cwd, argc == 1 ? "." : argv[1]);
+  path_t *path = path_open(proc, proc->cwd, argc == 1 ? "." : argv[1]);
   if (!path) {
     WRITE_S("ls: invalid path\n");
     return;
@@ -18,17 +18,17 @@ void ls(process_t *proc, uint8_t argc, char **argv) {
   fs_node_t *curr = path->depth ? path->stack[path->depth - 1] : proc->root;
   if (!curr->is_dir) {
     WRITE_S("ls: can not list a file\n");
-    path_close(path);
+    path_close(proc, path);
     return;
   }
 
   uint8_t j = 0;
-  fs_node_t *item = fs_open_at(curr, j++);
+  fs_node_t *item = fs_open_at(proc, curr, j++);
   while (item) {
     WRITE_D(item->name);
     WRITE_S("\n");
-    fs_close(item);
-    item = fs_open_at(curr, j++);
+    fs_close(proc, item);
+    item = fs_open_at(proc, curr, j++);
   }
-  path_close(path);
+  path_close(proc, path);
 }
diff --git a/src/app/terminal.c b/src/app/terminal.c
index f5f7c6e..2629f2f 100644
--- a/src/app/terminal.c
+++ b/src/app/terminal.c
@@ -56,13 +56,13 @@ static void cd(process_t *proc, uint8_t argc, char **argv) {
     return;
   }
 
-  path_t *new = path_open(proc->root, proc->cwd, argv[1]);
+  path_t *new = path_open(proc, proc->cwd, argv[1]);
   if (!new) {
     WRITE_S("cd: path does not exist\n");
     return;
   }
 
-  path_close(proc->cwd);
+  path_close(proc, proc->cwd);
   proc->cwd = new;
 }
 
@@ -270,9 +270,7 @@ void terminal(process_t *p, __attribute__((unused)) uint8_t argc, __attribute__(
 
   proc = p;
 
-  char *greeting = string_format("Welcome to FreywarOS v%s!\n\n", VERSION);
-  WRITE_D(greeting);
-  memory_free(greeting);
+  WRITE_D("Welcome to FreywarOS v" VERSION "!\n\n");
 
   print_prompt();
 
diff --git a/src/bootloader.asm b/src/bootloader.asm
index 6be8331..015be8d 100644
--- a/src/bootloader.asm
+++ b/src/bootloader.asm
@@ -276,23 +276,30 @@ protected_mode:
     mov ss, ax
     mov esp, 0x00090000
 
-    ; zero page table memory at 0x00010000 (3 pages = 768 dwords)
+    ; zero page table memory at 0x00010000
     mov edi, 0x00010000
-    mov ecx, 768
+    mov ecx, 256 * 5
     xor eax, eax
     rep stosd
 
     ; PML4[0] -> PDPT at 0x00011000
     mov dword [0x00010000], 0x00011003
-    ; PDPT[0] -> PD at 0x00012000
-    mov dword [0x00011000], 0x00012003
+    ; PML4[511] -> PDPT at 0x00012000
+    mov dword [0x00010FF8], 0x00012003
+    ; PML4[0].PDPT[0] -> PD at 0x00013000
+    mov dword [0x00011000], 0x00013003
+    ; PML4[511].PDPT[510] -> PD at 0x00014000
+    mov dword [0x00012FF0], 0x00014003
     ; PD: fill 64 entries, each mapping 2MB
-    mov edi, 0x00012000
+    mov edi, 0x00013000
     mov eax, 0x00000083   ; present, writable, huge page, base 0
     mov ecx, 64
 
 .fill_pd:
+    mov ebx, edi
+    add ebx, 0x1000
     mov dword [edi], eax
+    mov dword [ebx], eax
     add edi, 8
     add eax, 0x00200000   ; next 2MB
     loop .fill_pd
@@ -327,11 +334,11 @@ long_mode:
     mov ds, ax
     mov es, ax
     mov ss, ax
-    mov rsp, 0x0000000000090000
+    mov rsp, 0xFFFFFFFF80090000
 
     xor rax, rax
     xor rbx, rbx
     xor rcx, rcx
     xor rdx, rdx
 
-    jmp 0x00020000
+    jmp 0xFFFFFFFF80020000
diff --git a/src/fat16.c b/src/fat16.c
index d659316..1ad5dab 100644
--- a/src/fat16.c
+++ b/src/fat16.c
@@ -1,10 +1,9 @@
 #include "src/fat16.h"
 #include "src/ata.h"
-#include "src/fs.h"
 #include "src/memory.h"
+#include "src/process.h"
 #include "src/string.h"
 #include "src/util.h"
-#include <stdint.h>
 
 #define SECTOR_SIZE 512
 #define FIRST_PARTITION_SECTOR 2048
@@ -74,11 +73,11 @@ static void from_8_3(const char *name, const char *extension, char *output) {
   }
 }
 
-fs_node_t *fat16_mount() { // Assuming one partition.
+fs_node_t *fat16_mount(process_t *kernel) { // Assuming one partition.
   uint8_t sector[512];
   ata_read_sectors(FIRST_PARTITION_SECTOR, 1, &sector);
   memory_copy(sector + 11, sizeof(fat16_bpb_t), &bpb);
-  fat16_node_t *node = memory_allocate(sizeof(fat16_node_t));
+  fat16_node_t *node = memory_allocate(kernel, sizeof(fat16_node_t));
   node->base.type = FAT16;
   node->base.name[0] = node->entry.name[0] = '/';
   node->base.size = node->entry.size = sizeof(fat16_dir_entry_t) * bpb.root_entry_count;
@@ -86,23 +85,23 @@ fs_node_t *fat16_mount() { // Assuming one partition.
   return fs = (fs_node_t *)node;
 }
 
-static void ensure_fat() {
+static void ensure_fat(process_t *proc) {
   ASSERT(bpb.sectors_per_fat < 256, "ensure_fat: big FAT not implemented")
   if (!fat) {
-    fat = memory_allocate(bpb.sectors_per_fat * SECTOR_SIZE);
+    fat = memory_allocate(proc->kernel, bpb.sectors_per_fat * SECTOR_SIZE);
     ata_read_sectors(FIRST_PARTITION_SECTOR + bpb.reserved_sectors, (uint8_t)bpb.sectors_per_fat, fat);
   }
 }
 
-static fat16_dir_entry_t *load_directory(fat16_node_t *directory) {
+static fat16_dir_entry_t *load_directory(process_t *proc, fat16_node_t *directory) {
   fat16_dir_entry_t *entries;
 
   if (!directory->entry.first_cluster) {
     uint8_t sectors = (uint8_t)((directory->base.size + SECTOR_SIZE - 1) / SECTOR_SIZE);
-    entries = memory_allocate(sectors * SECTOR_SIZE + sizeof(fat16_dir_entry_t)); // One extra as null terminator.
+    entries = memory_allocate(proc, sectors * SECTOR_SIZE + sizeof(fat16_dir_entry_t)); // One extra as null terminator.
     ata_read_sectors(FIRST_PARTITION_SECTOR + bpb.reserved_sectors + bpb.fats_count * bpb.sectors_per_fat, sectors, entries);
   } else {
-    ensure_fat();
+    ensure_fat(proc);
 
     uint16_t next_cluster = directory->entry.first_cluster;
     uint32_t cluster_count = 0;
@@ -110,8 +109,8 @@ static fat16_dir_entry_t *load_directory(fat16_node_t *directory) {
       cluster_count++;
       next_cluster = fat[next_cluster];
     }
-    entries =
-        memory_allocate(cluster_count * bpb.sectors_per_cluster * SECTOR_SIZE + sizeof(fat16_dir_entry_t)); // One extra as null terminator.
+    entries = memory_allocate(proc, cluster_count * bpb.sectors_per_cluster * SECTOR_SIZE +
+                                        sizeof(fat16_dir_entry_t)); // One extra as null terminator.
 
     uint8_t *chunk = (uint8_t *)entries;
     next_cluster = directory->entry.first_cluster;
@@ -128,12 +127,12 @@ static fat16_dir_entry_t *load_directory(fat16_node_t *directory) {
   return entries;
 }
 
-static fs_node_t *open_entry(const char *name, const fat16_dir_entry_t *entry) {
+static fs_node_t *open_entry(process_t *proc, const char *name, const fat16_dir_entry_t *entry) {
   if (!entry->name[0]) {
     return NUL;
   }
 
-  fat16_node_t *result = memory_allocate(sizeof(fat16_node_t));
+  fat16_node_t *result = memory_allocate(proc, sizeof(fat16_node_t));
   memory_copy((char *)name, string_length(name) + 1, &(result->base.name));
   result->base.type = FAT16;
   result->base.size = entry->size;
@@ -143,14 +142,14 @@ static fs_node_t *open_entry(const char *name, const fat16_dir_entry_t *entry) {
   return (fs_node_t *)result;
 }
 
-fs_node_t *fat16_open_by(const fs_node_t *directory, const char *name) {
+fs_node_t *fat16_open_by(process_t *proc, const fs_node_t *directory, const char *name) {
   ASSERT(directory->type == FAT16, "fat16_open_by: directory is not FAT16");
   ASSERT(directory->is_dir, "fat16_open_by: directory is not a directory");
 
   char name_8_3[12];
   to_8_3(name, name_8_3);
 
-  fat16_dir_entry_t *entries = load_directory((fat16_node_t *)directory);
+  fat16_dir_entry_t *entries = load_directory(proc, (fat16_node_t *)directory);
 
   fat16_dir_entry_t *entry = entries;
   while (entry->name[0]) {
@@ -160,16 +159,16 @@ fs_node_t *fat16_open_by(const fs_node_t *directory, const char *name) {
     entry++;
   }
 
-  fs_node_t *result = open_entry(name, entry);
-  memory_free(entries);
+  fs_node_t *result = open_entry(proc, name, entry);
+  memory_free(proc, entries);
   return result;
 }
 
-fs_node_t *fat16_open_at(const fs_node_t *directory, uint64_t index) {
+fs_node_t *fat16_open_at(process_t *proc, const fs_node_t *directory, uint64_t index) {
   ASSERT(directory->type == FAT16, "fat16_open_at: directory is not FAT16");
   ASSERT(directory->is_dir, "fat16_open_at: directory is not a directory");
 
-  fat16_dir_entry_t *entries = load_directory((fat16_node_t *)directory);
+  fat16_dir_entry_t *entries = load_directory(proc, (fat16_node_t *)directory);
 
   uint64_t ei = 0, vi = 0;
   while (entries[ei].name[0]) {
@@ -189,23 +188,23 @@ fs_node_t *fat16_open_at(const fs_node_t *directory, uint64_t index) {
   char name[13];
   from_8_3(entries[ei].name, entries[ei].ext, name);
 
-  fs_node_t *result = open_entry(name, entries + ei);
-  memory_free(entries);
+  fs_node_t *result = open_entry(proc, name, entries + ei);
+  memory_free(proc, entries);
   return result;
 }
 
-fs_node_t *fat16_open_again(const fs_node_t *source) {
-  fs_node_t *result = memory_allocate(sizeof(fat16_node_t));
+fs_node_t *fat16_open_again(process_t *proc, const fs_node_t *source) {
+  fs_node_t *result = memory_allocate(proc, sizeof(fat16_node_t));
   memory_copy(source, sizeof(fat16_node_t), result);
   return result;
 }
 
-void fat16_read(const fs_node_t *file, uint64_t offset, uint64_t size, void *to) {
+void fat16_read(process_t *proc, const fs_node_t *file, uint64_t offset, uint64_t size, void *to) {
   ASSERT(file->type == FAT16, "fat16_read: file is not FAT16");
   ASSERT(!file->is_dir, "fat16_read: can not read directory");
   ASSERT(file->size >= offset + size, "fat16_read: offset/size are out of bounds");
 
-  ensure_fat();
+  ensure_fat(proc);
 
   fat16_node_t *fat_file = (fat16_node_t *)file;
 
@@ -221,7 +220,7 @@ void fat16_read(const fs_node_t *file, uint64_t offset, uint64_t size, void *to)
 
   uint8_t *cursor = to;
 
-  uint8_t *tmp = memory_allocate(cluster_size);
+  uint8_t *tmp = memory_allocate(proc, cluster_size);
   ata_read_sectors(FIRST_PARTITION_SECTOR + bpb.reserved_sectors + bpb.sectors_per_fat * bpb.fats_count +
                        (bpb.root_entry_count * sizeof(fat16_dir_entry_t) + SECTOR_SIZE - 1) / SECTOR_SIZE +
                        bpb.sectors_per_cluster * (next_cluster - 2),
@@ -250,18 +249,18 @@ void fat16_read(const fs_node_t *file, uint64_t offset, uint64_t size, void *to)
     memory_copy(tmp, size, cursor);
   }
 
-  memory_free(tmp);
+  memory_free(proc, tmp);
 }
 
-void fat16_close(fs_node_t *node) {
+void fat16_close(process_t *proc, fs_node_t *node) {
   ASSERT(node->type == FAT16, "fat16_close: node is not FAT16");
   ASSERT(node != fs, "fat16_close: can not unmount FS");
-  memory_free(node);
+  memory_free(proc, node);
 }
 
-void fat16_unmount(fs_node_t *node) {
+void fat16_unmount(process_t *kernel, fs_node_t *node) {
   ASSERT(node->type == FAT16, "fat16_unmount: node is not FAT16");
   ASSERT(node == fs, "fat16_unmount: node is not filesystem");
-  memory_free(node);
+  memory_free(kernel, node);
   fs = NUL;
 }
diff --git a/src/fat16.h b/src/fat16.h
index e74abe6..d42b702 100644
--- a/src/fat16.h
+++ b/src/fat16.h
@@ -2,18 +2,20 @@
 
 #include "src/fs.h"
 
+typedef struct process process_t;
+
 #define FAT16 1
 
-fs_node_t *fat16_mount();
+fs_node_t *fat16_mount(process_t *kernel);
 
-fs_node_t *fat16_open_by(const fs_node_t *directory, const char *name);
+fs_node_t *fat16_open_by(process_t *proc, const fs_node_t *directory, const char *name);
 
-fs_node_t *fat16_open_at(const fs_node_t *directory, uint64_t index);
+fs_node_t *fat16_open_at(process_t *proc, const fs_node_t *directory, uint64_t index);
 
-fs_node_t *fat16_open_again(const fs_node_t *source);
+fs_node_t *fat16_open_again(process_t *proc, const fs_node_t *source);
 
-void fat16_read(const fs_node_t *file, uint64_t offset, uint64_t size, void *to);
+void fat16_read(process_t *proc, const fs_node_t *file, uint64_t offset, uint64_t size, void *to);
 
-void fat16_close(fs_node_t *node);
+void fat16_close(process_t *proc, fs_node_t *node);
 
-void fat16_unmount(fs_node_t *fs);
+void fat16_unmount(process_t *kernel, fs_node_t *fs);
diff --git a/src/fs.c b/src/fs.c
index 2c9fc13..fcb2c71 100644
--- a/src/fs.c
+++ b/src/fs.c
@@ -1,30 +1,31 @@
 #include "src/fs.h"
 #include "src/fat16.h"
+#include "src/process.h"
 
-fs_node_t *fs_mount() {
-  return fat16_mount();
+fs_node_t *fs_mount(process_t *kernel) {
+  return fat16_mount(kernel);
 }
 
-fs_node_t *fs_open_by(const fs_node_t *directory, const char *name) {
-  return fat16_open_by(directory, name);
+fs_node_t *fs_open_by(process_t *proc, const fs_node_t *directory, const char *name) {
+  return fat16_open_by(proc, directory, name);
 }
 
-fs_node_t *fs_open_at(const fs_node_t *directory, uint64_t index) {
-  return fat16_open_at(directory, index);
+fs_node_t *fs_open_at(process_t *proc, const fs_node_t *directory, uint64_t index) {
+  return fat16_open_at(proc, directory, index);
 }
 
-fs_node_t *fs_open_again(const fs_node_t *source) {
-  return fat16_open_again(source);
+fs_node_t *fs_open_again(process_t *proc, const fs_node_t *source) {
+  return fat16_open_again(proc, source);
 }
 
-void fs_read(const fs_node_t *file, uint64_t offset, uint64_t size, void *to) {
-  fat16_read(file, offset, size, to);
+void fs_read(process_t *proc, const fs_node_t *file, uint64_t offset, uint64_t size, void *to) {
+  fat16_read(proc, file, offset, size, to);
 }
 
-void fs_close(fs_node_t *node) {
-  fat16_close(node);
+void fs_close(process_t *proc, fs_node_t *node) {
+  fat16_close(proc, node);
 }
 
-void fs_unmount(fs_node_t *fs) {
-  fat16_unmount(fs);
+void fs_unmount(process_t *kernel, fs_node_t *fs) {
+  fat16_unmount(kernel, fs);
 }
diff --git a/src/fs.h b/src/fs.h
index cd1334a..45dc28c 100644
--- a/src/fs.h
+++ b/src/fs.h
@@ -4,6 +4,8 @@
 
 #define FILENAME_SIZE_LIMIT 255
 
+typedef struct process process_t;
+
 typedef struct fs_node {
   char name[FILENAME_SIZE_LIMIT + 1];
   uint32_t size;
@@ -12,16 +14,16 @@ typedef struct fs_node {
 } fs_node_t;
 
 
-fs_node_t *fs_mount();
+fs_node_t *fs_mount(process_t *kernel);
 
-fs_node_t *fs_open_by(const fs_node_t *directory, const char *name);
+fs_node_t *fs_open_by(process_t *proc, const fs_node_t *directory, const char *name);
 
-fs_node_t *fs_open_at(const fs_node_t *directory, uint64_t index);
+fs_node_t *fs_open_at(process_t *proc, const fs_node_t *directory, uint64_t index);
 
-fs_node_t *fs_open_again(const fs_node_t *source);
+fs_node_t *fs_open_again(process_t *proc, const fs_node_t *source);
 
-void fs_read(const fs_node_t *file, uint64_t offset, uint64_t size, void *to);
+void fs_read(process_t *proc, const fs_node_t *file, uint64_t offset, uint64_t size, void *to);
 
-void fs_close(fs_node_t *node);
+void fs_close(process_t *proc, fs_node_t *node);
 
-void fs_unmount(fs_node_t *fs);
+void fs_unmount(process_t *kernel, fs_node_t *fs);
diff --git a/src/kernel.c b/src/kernel.c
index f5ff1f0..621812a 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -32,6 +32,8 @@ __attribute__((interrupt)) void isr_ata_primary(__attribute__((unused)) struct i
   outb(0xA0, 0x20);
 }
 
+static process_t kernel_process;
+
 void kernel_main() {
   pic_init();
   idt_init();
@@ -42,15 +44,15 @@ void kernel_main() {
   idt_set_entry(46, isr_ata_primary, 0x8E);
   __asm__ volatile("sti");
 
-  memory_init();
+  memory_init(&kernel_process);
+  kernel_process.root = fs_mount(&kernel_process);
+  kernel_process.cwd = memory_allocate(&kernel_process, sizeof(path_t));
+  kernel_process.stdin = keyboard_init();
+  kernel_process.stdout = vga_init();
 
-  process_t *proc = memory_allocate(sizeof(process_t));
-  proc->cwd = memory_allocate(sizeof(path_t));
-  proc->root = fs_mount();
-  proc->stdin = keyboard_init();
-  proc->stdout = vga_init();
+  terminal(&kernel_process, 0, NUL);
 
-  terminal(proc, 0, NUL);
+  fs_unmount(&kernel_process, kernel_process.root);
 
   outw(0x604, 0x2000); // TODO: parse ACPI tables for real hardware
   __asm__ volatile("cli; hlt");
diff --git a/src/linker.ld b/src/linker.ld
index 07fcbff..af8bc01 100644
--- a/src/linker.ld
+++ b/src/linker.ld
@@ -1,7 +1,7 @@
 ENTRY(kernel_main)
 
 SECTIONS {
-    . = 0x0000000000020000;
+    . = 0xFFFFFFFF80020000;
 
     .text : {
         *(.text)
diff --git a/src/memory.c b/src/memory.c
index f3070b6..e8f6fec 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -1,9 +1,9 @@
 #include "src/memory.h"
 #include "src/panic.h"
+#include "src/process.h"
 #include "src/util.h"
-#include <stdint.h>
 
-#define MEMORY_SIZE 134217728
+#define MEMORY_SIZE 0x08000000
 #define PAGE_SIZE 4096
 #define PAGE_COUNT (MEMORY_SIZE / PAGE_SIZE)
 #define MAP_UNIT 64
@@ -49,29 +49,27 @@ __attribute__((unused)) static void memory_page_free(void *address) {
   }
 }
 
+#define KERNEL_VIRTUAL_BASE 0xFFFFFFFF80000000ULL
+#define PHYS_TO_VIRT(phys) ((void *)((uint64_t)(phys) + KERNEL_VIRTUAL_BASE))
+#define VIRT_TO_PHYS(virt) ((uint64_t)(virt) - KERNEL_VIRTUAL_BASE)
 #define HEAP_PAGE_COUNT 256
 
-typedef struct free_chunk {
-  uint64_t size; // header + data
-  struct free_chunk *next;
-} free_chunk_t;
-
-static free_chunk_t *free_list;
-
-void memory_init() {
-  free_list = memory_page_allocate();
+void memory_init(process_t *kernel) {
+  kernel->pml4 = PHYS_TO_VIRT(0x00010000);
+  // Assumes 0x0 -> KERNEL_VIRTUAL_BASE mapping and `memory_page_allocate` issuing continuous pages initially.
+  kernel->heap = PHYS_TO_VIRT(memory_page_allocate());
   for (uint64_t i = 1; i < HEAP_PAGE_COUNT; i++) {
-    memory_page_allocate(); // TODO Map the pages.
+    memory_page_allocate();
   }
-  free_list->size = HEAP_PAGE_COUNT * PAGE_SIZE;
-  free_list->next = NUL;
+  kernel->heap->size = HEAP_PAGE_COUNT * PAGE_SIZE;
+  kernel->heap->next = NUL;
 }
 
-void *memory_allocate(uint64_t size) {
+void *memory_allocate(process_t *proc, uint64_t size) {
   size = sizeof(free_chunk_t) + (size + 7) & (uint64_t)~7;
 
   free_chunk_t *prev = NUL;
-  free_chunk_t *curr = free_list;
+  free_chunk_t *curr = proc->heap;
 
   while (curr) {
     if (curr->size >= size + (sizeof(free_chunk_t) + 8)) {
@@ -85,7 +83,7 @@ void *memory_allocate(uint64_t size) {
       if (prev) {
         prev->next = curr->next;
       } else {
-        free_list = curr->next;
+        proc->heap = curr->next;
       }
       void *result = (void *)((uint8_t *)curr + sizeof(free_chunk_t));
       memory_set(0, size - sizeof(free_chunk_t), result);
@@ -99,9 +97,9 @@ void *memory_allocate(uint64_t size) {
   return 0;
 }
 
-void memory_free(void *pointer) {
+void memory_free(process_t *proc, void *pointer) {
   free_chunk_t *chunk = (free_chunk_t *)((uint8_t *)pointer - sizeof(free_chunk_t));
-  chunk->next = free_list;
-  free_list = chunk;
+  chunk->next = proc->heap;
+  proc->heap = chunk;
   // TODO Merge adjacent free chunks.
 }
diff --git a/src/memory.h b/src/memory.h
index 137e30c..27d5d5b 100644
--- a/src/memory.h
+++ b/src/memory.h
@@ -3,11 +3,18 @@
 #include "src/panic.h"
 #include <stdint.h>
 
-void memory_init();
+typedef struct process process_t;
 
-void *memory_allocate(uint64_t size);
+typedef struct free_chunk {
+  uint64_t size; // header + data
+  struct free_chunk *next;
+} free_chunk_t;
 
-void memory_free(void *pointer);
+void memory_init(process_t *kernel);
+
+void *memory_allocate(process_t *proc, uint64_t size);
+
+void memory_free(process_t *proc, void *pointer);
 
 static inline void memory_set(uint8_t value, uint64_t bytes, void *to) {
   __asm__ volatile("rep stosb" : "=D"(to), "=c"(bytes) : "D"(to), "a"(value), "c"(bytes) : "memory");
diff --git a/src/path.c b/src/path.c
index fb488ce..7b39f5f 100644
--- a/src/path.c
+++ b/src/path.c
@@ -1,18 +1,17 @@
 #include "src/path.h"
-#include "src/fs.h"
 #include "src/memory.h"
+#include "src/process.h"
 #include "src/string.h"
 #include "src/util.h"
-#include <stdint.h>
 
-path_t *path_open(const fs_node_t *root, const path_t *source, char *path) {
-  path_t *result = memory_allocate(sizeof(path_t));
+path_t *path_open(process_t *proc, const path_t *source, char *path) {
+  path_t *result = memory_allocate(proc, sizeof(path_t));
 
   char *path_components[PATH_DEPTH];
   uint8_t path_length = (uint8_t)string_split(path, '/', PATH_DEPTH, path_components);
   if (!string_empty(path_components[0])) {
     for (uint8_t i = 0; i < source->depth; i++) {
-      result->stack[result->depth++] = fs_open_again(source->stack[i]);
+      result->stack[result->depth++] = fs_open_again(proc, source->stack[i]);
     }
   }
 
@@ -21,13 +20,13 @@ path_t *path_open(const fs_node_t *root, const path_t *source, char *path) {
       continue;
     } else if (string_equal(path_components[i], "..")) {
       if (result->depth) {
-        fs_close(result->stack[--result->depth]);
+        fs_close(proc, result->stack[--result->depth]);
       }
     } else {
-      const fs_node_t *prev = result->depth ? result->stack[result->depth - 1] : root;
-      fs_node_t *next = prev->is_dir ? fs_open_by(prev, path_components[i]) : NUL;
+      const fs_node_t *prev = result->depth ? result->stack[result->depth - 1] : proc->root;
+      fs_node_t *next = prev->is_dir ? fs_open_by(proc, prev, path_components[i]) : NUL;
       if (!next || result->depth >= PATH_DEPTH) {
-        path_close(result);
+        path_close(proc, result);
         return NUL;
       } else {
         result->stack[result->depth++] = next;
@@ -38,9 +37,9 @@ path_t *path_open(const fs_node_t *root, const path_t *source, char *path) {
   return result;
 }
 
-void path_close(path_t *path) {
+void path_close(process_t *proc, path_t *path) {
   for (uint64_t i = 0; i < path->depth; i++) {
-    fs_close(path->stack[i]);
+    fs_close(proc, path->stack[i]);
   }
-  memory_free(path);
+  memory_free(proc, path);
 }
diff --git a/src/path.h b/src/path.h
index 9ccd20a..2835779 100644
--- a/src/path.h
+++ b/src/path.h
@@ -1,15 +1,16 @@
 #pragma once
 
 #include "src/fs.h"
-#include <stdint.h>
 
 #define PATH_DEPTH 255
 
+typedef struct process process_t;
+
 typedef struct {
   fs_node_t *stack[PATH_DEPTH];
   uint8_t depth;
 } path_t;
 
-path_t *path_open(const fs_node_t *root, const path_t *source, char *path);
+path_t *path_open(process_t *proc, const path_t *source, char *path);
 
-void path_close(path_t *path);
+void path_close(process_t *proc, path_t *path);
diff --git a/src/process.h b/src/process.h
index fc2a4e1..5bdd17a 100644
--- a/src/process.h
+++ b/src/process.h
@@ -1,13 +1,18 @@
 #pragma once
 
-#include "src/fs.h"
 #include "src/path.h"
 #include "src/stream.h"
 #include "src/string.h"
+#include <stdint.h>
 
-typedef struct {
-  path_t *cwd;
+typedef struct free_chunk free_chunk_t;
+
+typedef struct process {
+  struct process *kernel;
+  uint64_t *pml4;
+  free_chunk_t *heap;
   fs_node_t *root;
+  path_t *cwd;
   stream_t *stdin;
   stream_t *stdout;
 } process_t;
diff --git a/src/string.c b/src/string.c
index add1fda..27f3e3e 100644
--- a/src/string.c
+++ b/src/string.c
@@ -1,7 +1,5 @@
 #include "src/string.h"
-#include "src/memory.h"
 #include <stdarg.h>
-#include <stdint.h>
 
 uint8_t bytes_equal(const char *l, const char *r, uint64_t count) {
   while (count--) {
@@ -164,41 +162,39 @@ uint64_t string_uint_to_hex(uint64_t value, uint64_t max, char *result) {
   return i;
 }
 
-char *string_format(const char *format, ...) {
+uint64_t string_format(const char *format, uint64_t max, char *output, ...) {
   va_list args;
-  va_start(args, format);
+  va_start(args, output);
 
-  uint64_t limit = 1023;
-
-  char *result = memory_allocate(limit + 1);
+  uint64_t limit = max - 1;
 
   uint64_t fi = 0, ri = 0;
   while (format[fi] && ri < limit) {
     if (format[fi] != '%') {
-      result[ri++] = format[fi++];
+      output[ri++] = format[fi++];
     } else {
       switch (format[fi + 1]) {
       case 'c':
-        result[ri++] = (char)va_arg(args, int);
+        output[ri++] = (char)va_arg(args, int);
         fi += 2;
         break;
       case 'd':
-        string_int_to_decimal(va_arg(args, int64_t), limit - ri, result + ri);
-        while (result[ri]) {
+        string_int_to_decimal(va_arg(args, int64_t), limit - ri, output + ri);
+        while (output[ri]) {
           ri++;
         }
         fi += 2;
         break;
       case 'u':
-        string_uint_to_decimal(va_arg(args, uint64_t), limit - ri, result + ri);
-        while (result[ri]) {
+        string_uint_to_decimal(va_arg(args, uint64_t), limit - ri, output + ri);
+        while (output[ri]) {
           ri++;
         }
         fi += 2;
         break;
       case 'x':
-        string_uint_to_hex(va_arg(args, uint64_t), limit - ri, result + ri);
-        while (result[ri]) {
+        string_uint_to_hex(va_arg(args, uint64_t), limit - ri, output + ri);
+        while (output[ri]) {
           ri++;
         }
         fi += 2;
@@ -206,25 +202,26 @@ char *string_format(const char *format, ...) {
       case 's': {
         char *s = va_arg(args, char *);
         while (*s && ri < limit) {
-          result[ri++] = *s;
+          output[ri++] = *s;
           s++;
         }
         fi += 2;
         break;
       }
       case '%': {
-        result[ri++] = '%';
+        output[ri++] = '%';
         fi += 2;
         break;
       }
       default:
-        result[ri++] = format[fi++];
-        result[ri++] = format[fi++];
+        output[ri++] = format[fi++];
+        output[ri++] = format[fi++];
         break;
       }
     }
   }
-  result[ri] = '\0';
+  output[ri] = '\0';
   va_end(args);
-  return result;
+
+  return ri;
 }
diff --git a/src/string.h b/src/string.h
index 37de9f6..5c28377 100644
--- a/src/string.h
+++ b/src/string.h
@@ -20,4 +20,4 @@ uint64_t string_int_to_decimal(int64_t value, uint64_t max, char *result);
 
 uint64_t string_uint_to_hex(uint64_t value, uint64_t max, char *result);
 
-char *string_format(const char *format, ...);
+uint64_t string_format(const char *format, uint64_t max, char *output, ...);
diff --git a/src/vga.c b/src/vga.c
index 49e9e69..6203d0e 100644
--- a/src/vga.c
+++ b/src/vga.c
@@ -1,9 +1,8 @@
 #include "src/vga.h"
 #include "src/memory.h"
 #include "src/util.h"
-#include <stdint.h>
 
-static uint16_t *vga = (uint16_t *)0x000B8000;
+static uint16_t *vga = (uint16_t *)0xFFFFFFFF800B8000;
 static uint16_t color = (uint16_t)0x0F << 8;
 static uint16_t offset = 0;