Updated kernel to now have its stack past 0xc0000000. Implemented context switching.

src/boot_stage2/main.c

@@ -167,7 +167,7 @@ void main() {
   mark_unavailble(0xc0502000, 0x1000, vm_bitmap);
   mark_unavailble(0xc0600000, 0x20000, vm_bitmap);
   mark_unavailble(0xc0620000, 0x20000, vm_bitmap);
-  mark_unavailble(0x8a000, 0x6000, vm_bitmap);
+  mark_unavailble(0xc1000000, 0x6000, vm_bitmap);
 
   // Map the bitmap 
   map_many_4k_phys_to_virt(0x100000, 0xc0600000, kernel_page_directory, kernel_page_tables, 32);
@@ -175,7 +175,9 @@ void main() {
   map_many_4k_phys_to_virt(0x522000, 0xc0620000, kernel_page_directory, kernel_page_tables, 32);
 
   map_4k_phys_to_virt(0x8000, 0x8000, kernel_page_directory, kernel_page_tables);
+  // Map the stack
   map_many_4k_phys_to_virt(0x8a000, 0x8a000, kernel_page_directory, kernel_page_tables, 6);
+  map_many_4k_phys_to_virt(0x8a000, 0xc1000000, kernel_page_directory, kernel_page_tables, 6);
 
   load_file("KERNEL  BIN", kernel_location);
 

src/kernel/entry.asm

@@ -1,6 +1,7 @@
 [BITS 32]
 
 _start:
+  mov esp, 0xc1005ffc
   jmp main
 
 extern main

src/kernel/global.cpp

@@ -3,6 +3,7 @@
 namespace Global {
   Allocator* allocator = 0;
   Kernel* kernel = 0;
+  Process* currentProc = 0;
 }
 
 void* operator new (uint32_t size) {

src/kernel/global.h

@@ -5,10 +5,12 @@
 
 class Kernel;
 class Allocator;
+class Process;
 
 namespace Global {
   extern Allocator* allocator;
   extern Kernel* kernel;
+  extern Process* currentProc;
 }
 
 void* operator new (uint32_t size);

src/kernel/idt.cpp

@@ -22,14 +22,89 @@ __attribute__((interrupt)) void interrupt_20(interrupt_frame* frame) {
 __attribute__((interrupt)) void page_fault(interrupt_frame* frame, uint32_t err_code) {
   uint32_t problem_address;
   asm("mov %%cr2, %0" : "=a" (problem_address) :);
-  printf("Page Fault at %x\n", problem_address);
-  asm("hlt");
+  printf("(EIP %x): Page Fault at %x\n", frame->eip, problem_address);
+  while (1) asm("hlt");
 }
 
 __attribute__((interrupt)) void ignore_interrupt(interrupt_frame* frame) {
   outb(0x20, 0x20);
 }
 
+__attribute__((interrupt)) void gpf(interrupt_frame* frame, uint32_t err_code) {
+  printf("General Protection Fault %d\n", err_code);
+  while (1) asm("hlt");
+}
+
+__attribute__((interrupt)) void context_switch(interrupt_frame* frame) {
+  asm ("cli"); // Disable interrupts whilst handling the context switch.
+  asm ("pusha"); // Push registers to the stack
+
+  Process* currentProc = Global::currentProc;
+  Process* nextProc = 0;
+  if (currentProc) {
+    xnoe::linkedlist<Process*>* processes = &Global::kernel->processes;
+    
+    // This cursed bit of code first determines if the processes list is longer than 1 and if it is
+    // - Determines if it has 2 or more elements
+    //   - If it has two, swap the first and last, update prev and next of each to be null or the other item
+    //   - If it has more than two, swap the first and last, then swap their next and prevs, and set the 
+    //     other value to null
+    if (processes->start->next != 0) {
+      if (processes->end->prev == processes->start) {
+        xnoe::linkedlistelem<Process*>* tmp = processes->start;
+        processes->start = processes->end;
+        processes->end = tmp;
+
+        processes->start->prev = 0;
+        processes->end->next = 0;
+        processes->end->prev = processes->start;
+        processes->start->next = processes->end;
+      } else {
+        xnoe::linkedlistelem<Process*>* tmp = processes->start;
+        processes->start = processes->end;
+        processes->end = tmp;
+
+        processes->start->next = processes->end->next;
+        processes->end->prev = processes->start->prev;
+
+        processes->start->prev = 0;
+        processes->end->next = 0;
+
+        processes->start->next->prev = processes->start;
+        processes->end->prev->next = processes->end;
+      }
+
+      // Get the next process.
+      nextProc = processes->start->elem;
+    }
+
+    Global::currentProc = nextProc;
+
+    uint32_t cESP;
+    asm volatile ("mov %%esp, %0" : "=a" (cESP) :);
+    currentProc->esp = cESP; // Store the current ESP of the current process process.
+
+    // Select the next processes page directory
+    asm volatile ("mov %0, %%cr3" : : "r" (nextProc->PD->phys_addr)); 
+    // Restore ESP of the new process.
+    asm volatile ("mov %0, %%esp" : : "m" (Global::kernel->processes.start->elem->esp));
+    // Restore registers
+    asm ("popa"); 
+    
+    // Clear the garbage that was on the stack from previous switch_context call.
+    asm ("add $44, %esp");
+
+    // Pop EBP
+    asm ("pop %ebp");
+
+    // Re-enable interrupts.
+    asm ("sti");
+
+    // Manually perform iret.
+    asm ("iret");
+  }
+}
+
 void init_idt() {
   idt_desc desc = {.size = 256 * sizeof(GateEntry) - 1, .offset = (uint32_t)idt};
   asm volatile("lidt %0" : : "m" (desc));
@@ -37,7 +112,9 @@ void init_idt() {
     set_entry(i, 0x08, &ignore_interrupt, 0x8E);
   
   set_entry(0x20, 0x08, &interrupt_20, 0x8E);
+  set_entry(0xD, 0x08, &gpf, 0x8E);
   set_entry(0xE, 0x08, &page_fault, 0x8E);
+  set_entry(0x80, 0x08, &context_switch, 0x8E);
 
   outb(0x20, 0x11);
   outb(0xA0, 0x11);

src/kernel/idt.h

@@ -3,13 +3,14 @@
 
 #include "types.h"
 #include "screenstuff.h"
+#include "global.h"
+#include "kernel.h"
 
 struct interrupt_frame {
-    uint16_t ip;
+    uint32_t eip;
     uint16_t cs;
-    uint16_t flags;
-    uint16_t sp;
-    uint16_t ss;
+    uint16_t _ignored0;
+    uint32_t eflags;
 };
 extern void load_idt();
 void set_entry(uint8_t interrupt_number, uint16_t code_segment, void* handler, uint8_t type);

src/kernel/kernel.cpp

@@ -6,6 +6,10 @@ Kernel::Kernel(PageDirectory* page_directory, PageMap* phys, PageMap* virt, uint
   this->currentPID = 1;
   Global::allocator = this;
   Global::kernel = this;
+
+  Global::currentProc = 0;
+
+  this->processes.append(this);
 }
 
 void Kernel::init_kernel() {
@@ -13,8 +17,11 @@ void Kernel::init_kernel() {
 }
 
 Process* Kernel::createProcess() {
-  Process* p = new Process(currentPID);
+  Process* p = new Process(currentPID, this->PD, 0xc0000000);
   this->pid_map->set(currentPID, p);
   currentPID++;
+
+  this->processes.append(p);
+
   return p;
 }

src/kernel/kernel.h

@@ -6,12 +6,12 @@
 #include "global.h"
 
 class Kernel : public Process {
-private:
+public:
   uint32_t currentPID;
 
-public:
   xnoe::hashtable<uint32_t, Process*>* pid_map; // Map of PIDs -> Process*s
-  uint32_t current_PID;
+
+  xnoe::linkedlist<Process*> processes;
 
   Kernel(PageDirectory* page_directory, PageMap* phys, PageMap* virt, uint32_t virt_alloc_base);
 

src/kernel/kmain.cpp

@@ -47,10 +47,15 @@ int main() {
   
   term->printf("KERNEL OK!\n");
 
-  kernel.createProcess();
+  Process* p = kernel.createProcess();
 
-  term->deactivate();
-  term2->activate();
+  //term->deactivate();
+  //term2->activate();
+
+  Global::currentProc = &kernel;
+  asm ("int $0x80");
+
+  term->printf("\n\nIf you are reading this, the XnoeOS kernel successfully switched contexts to another process, and then switched contexts back to the kernel. Therefore we can conclude that context switching works.");
 
   while (1);
 

src/kernel/memory.cpp

@@ -88,8 +88,10 @@ PageTable::PageTable(uint32_t phys, uint32_t virt) {
 }
 
 PageTable::PageTable(){
-  virt_addr = new PTE[1024];
-  phys_addr = Global::allocator->virtual_to_physical(virt_addr);
+  virt_addr = new PTE[2048];
+  while ((uint32_t)this->virt_addr & 0xfff || (uint32_t)this->virt_addr % 0x4)
+    this->virt_addr++;
+  phys_addr = (Global::allocator->virtual_to_physical(virt_addr)) >> 12;
 
   page_table = (PTE*)virt_addr;
 }
@@ -143,8 +145,11 @@ PageDirectory::PageDirectory(PDE* page_directory, uint32_t phys_addr, uint32_t o
 
 PageDirectory::PageDirectory() {
   this->page_tables = (PageTable*)this->__page_tables;
-  this->page_directory = new PDE[1024];
+  this->page_directory = new PDE[2048];
+  while ((uint32_t)this->page_directory & 0xfff || (uint32_t)this->page_directory % 0x4)
+    this->page_directory++;
   memset((uint8_t*)this->page_tables, sizeof(PageTable) * 1024, 0);
+  memset((uint8_t*)this->page_directory, sizeof(PDE) * 1024, 0);
   this->phys_addr = Global::allocator->virtual_to_physical(this->page_directory);
 }
 
@@ -180,11 +185,11 @@ void PageDirectory::unmap(uint32_t virt) {
 
 uint32_t PageDirectory::virtual_to_physical(uint32_t virt) {
   split_addr* split = (split_addr*)&virt;
-  return page_tables[split->pd_index].get_physical_address(split->pt_index);
+  return page_tables[split->pd_index].get_physical_address(split->pt_index) + split->page_offset;
 }
 
 void PageDirectory::select() {
-  asm volatile("mov %0, %%eax; mov %%eax, %%cr3" : : "m" (phys_addr));
+  asm volatile("mov %0, %%cr3" : : "r" (phys_addr));
 }
 
 PageMap* Allocator::phys;
@@ -205,7 +210,6 @@ Allocator::Allocator(PageDirectory* page_directory, PageMap* virt, uint32_t virt
 }
 
 void* Allocator::allocate(uint32_t size) {
-  asm("mov $0x0, 0x8a000");
   uint32_t count = (size + (4096 - size % 4096)) / 4096;
 
   uint32_t virt_addr = virt->find_next_available_from(this->virt_alloc_base, count);
@@ -214,7 +218,6 @@ void* Allocator::allocate(uint32_t size) {
   for (int i=0; i<count; i++) {
     uint32_t phys_addr = this->phys->find_next_available_from(0);
     this->phys->mark_unavailable(phys_addr);
-    asm("mov $0xdead, 0x8a000");
     this->PD->map(phys_addr, virt_addr + 4096 * i);
   }
 

src/kernel/memory.h

@@ -51,13 +51,14 @@ struct PageTable {
 
 class PageDirectory {
 private:
-  PDE* page_directory;
   uint8_t __page_tables[sizeof(PageTable) * 1024];
   PageTable* page_tables;
 
+public:
   uint32_t phys_addr;
 
-public:
+  PDE* page_directory;
+  
   PageDirectory(PDE* page_directories, uint32_t phys_addr, uint32_t offset);
   PageDirectory();
 
@@ -74,10 +75,10 @@ protected:
   static PageMap* phys;
   PageMap* virt;
 
-  PageDirectory* PD;
-
   uint32_t virt_alloc_base;
 public:
+  PageDirectory* PD;
+
   Allocator(PageDirectory* page_directory, PageMap* phys, PageMap* virt, uint32_t virt_alloc_base);
   Allocator(PageDirectory* page_directory, PageMap* virt, uint32_t virt_alloc_base);
   virtual void* allocate(uint32_t size);

src/kernel/process.cpp

@@ -26,11 +26,80 @@ Process::Process(uint32_t PID)
 : Allocator(new PageDirectory, new PageMap, 0) {
   this->PID = PID;
   this->page_remaining = 0;
-  this->last_page_pointer = virt_alloc_base;
-  this->stack = new uint8_t[0x8000];
+  this->last_page_pointer = 0;
+  this->stack = this->allocate(0x8000);
+}
+
+Process::Process(uint32_t PID, PageDirectory* inherit, uint32_t inheritBase)
+: Allocator(new PageDirectory, new PageMap, 0) {
+  this->PID = PID;
+  this->page_remaining = 0;
+  this->last_page_pointer = 0;
+
+  for (int index = inheritBase >> 22; index < 1024; index++)
+    this->PD->page_directory[index] = inherit->page_directory[index];
+
+  this->stack = this->allocate(0x8000);
+
+  uint32_t pCR3;
+  asm ("mov %%cr3, %0" : "=a" (pCR3) :);
+  this->PD->select();
+  
+  // We also need to initialise ESP and the stack
+  uint32_t* stack32 = ((uint32_t)this->stack + 0x8000);
+  printf("stack32: %x\n", stack32);
+  stack32--;
+  *stack32 = 0x0; // EFLAGS
+  stack32--;
+  *stack32 = 8; // CS 0x08
+  stack32--;
+  *stack32 = 0x14; // Execution will begin from 0x14
+
+  stack32--;
+  *stack32 = ((uint32_t)this->stack + 0x8000); // EBP
+
+  stack32 -= 11;
+
+  stack32--;
+  *stack32 = 0; // EAX
+  stack32--;
+  *stack32 = 0; // ECX
+  stack32--;
+  *stack32 = 0;  // EDX
+  stack32--;
+  *stack32 = 0;  // EBX
+  stack32--;
+  *stack32 = 0; // ESP
+  stack32--;
+  *stack32 = (uint32_t)this->stack + 0x7ffc; // EBP
+  stack32--;
+  *stack32 = 0; // ESI
+  stack32--;
+  *stack32 = 0; // EDI
+
+  this->esp = stack32;
+  printf("this->esp: %x\n", stack32);
+
+  /*((uint8_t*)this->stack)[0] = 0xe9;
+  ((uint8_t*)this->stack)[1] = 0xfb;
+  ((uint8_t*)this->stack)[2] = 0xff;
+  ((uint8_t*)this->stack)[3] = 0xff;
+  ((uint8_t*)this->stack)[4] = 0xff;*/
+
+  ((uint8_t*)this->stack)[0] = 0xcd;
+  ((uint8_t*)this->stack)[1] = 0x80;
+
+  asm ("mov %0, %%cr3" : : "r" (pCR3));
 }
 
 void* Process::allocate(uint32_t size) {
+  bool switched_PD = false;
+  uint32_t pCR3;
+  asm ("mov %%cr3, %0" : "=a" (pCR3) :);
+  if (Global::currentProc != this) {
+    switched_PD = true;
+    this->PD->select();
+  }
   void* ptr;
   // Determine if there's enough space to just allocate what's been requested
   if (size < this->page_remaining) {
@@ -46,7 +115,7 @@ void* Process::allocate(uint32_t size) {
     uint32_t pages = size / 4096;
     uint32_t remainder = 4096 - (size % 4096);
 
-    ptr = Allocator::allocate(size);
+    ptr = this->Allocator::allocate(size);
 
     // Update local values
     this->last_page_pointer = ptr + pages * 4096;
@@ -61,6 +130,9 @@ void* Process::allocate(uint32_t size) {
 
     ptr += elem_size;
   }
+
+  asm ("mov %0, %%cr3" : : "r" (pCR3));
+
   return ptr;
 }
 
@@ -68,7 +140,7 @@ void Process::deallocate(uint32_t virt_addr) {
   xnoe::Maybe<xnoe::linkedlistelem<AllocTracker>*> alloc_tracker = this->get_alloc_tracker(virt_addr);
   if (alloc_tracker.is_ok()) {
     AllocTracker* ac = &alloc_tracker.get()->elem;
-    ac->alloc_count -= 1;
+    ac->alloc_count--;
     if (ac->alloc_count == 0) {
       void* base = ac->page_base;
       uint32_t count = ac->page_size;

src/kernel/process.h

@@ -32,8 +32,11 @@ private:
   xnoe::Maybe<xnoe::linkedlistelem<AllocTracker>*> get_alloc_tracker(uint32_t address);
 
 public:
+  uint32_t esp;
+
   Process(uint32_t PID, void* stack, PageDirectory* page_directory, PageMap* phys, PageMap* virt, uint32_t virt_alloc_base);
   Process(uint32_t PID);
+  Process(uint32_t PID, PageDirectory* inherit, uint32_t inheritBase);
 
   void* allocate(uint32_t size) override;
   void deallocate(uint32_t virt_addr) override;