Rewrote physical memory allocator

The physical memory allocator now uses a buddy allocator instead of a stack.

Also moved some of the platform-independent context code to kernel.c.

src/x86/context.c

@@ -4,54 +4,17 @@
 #include "heap.h"
 #include "string.h"
 #include "system.h"
-#include "x86/processstate.h"
-
-void *initialize_context(void *task_entry)
-{
-    physaddr_t stack_frame = reserve_page();
-    if(stack_frame % page_size != 0)
-    {
-        return NULL;
-    }
-    map_page((void*)&_kernel_start - page_size, stack_frame, PAGE_RW | PAGE_USERMODE);
-    unmap_page((void*)&_kernel_start - (2 * page_size));
-    struct process_context_t *context = kmalloc(sizeof(struct process_context_t));
-    if(context != NULL)
-    {
-       memset(context, 0, sizeof(struct process_context_t));
-       uint32_t flags;
-       asm("pushf; "
-           "mov (%%esp), %0; "
-           "popf; "
-           : "=r"(flags));
-       context->cs = 0x1B;
-       context->eip = (uint32_t)task_entry;
-       context->flags = (flags & ~0xFD) | 0x200;
-       context->ss = 0x23;
-       context->esp = &_kernel_start;
-       context->ebp = &_kernel_start;
-    }
-    return (void*)context;
-}
-
-void destroy_context(void *ctx)
-{
-    kfree(ctx);
-}
-
-void save_context(struct process_context_t *context)
-{
-    kernel_store_active_context(context, sizeof(*context));
-}
 
 void set_context_pc(struct process_context_t *context, void *pc)
 {
     context->eip = pc;
+    context->cs = 0x1B;
 }
 
 void set_context_stack(struct process_context_t *context, void *stack)
 {
-    context->esp = stack;
+    context->gp_registers[7] = stack;
+    context->ss = 0x23;
 }
 
 void set_context_flags(struct process_context_t *context, unsigned long flags)
@@ -61,5 +24,5 @@ void set_context_flags(struct process_context_t *context, unsigned long flags)
 
 void set_context_return(struct process_context_t *context, unsigned long value)
 {
-    context->eax = value;
+    context->gp_registers[0] = value;
 }

src/x86/load_context.S

@@ -7,8 +7,8 @@
 .type load_context, @function
 load_context:
     mov 4(%esp), %eax
-    push 0x1C(%eax)
     push 0x20(%eax)
+    push 0x1C(%eax)
     push 0x2C(%eax)
     push 0x24(%eax)
     push 0x28(%eax)
@@ -19,10 +19,11 @@ load_context:
     mov 0x10(%eax), %edi
     mov 0x14(%eax), %esi
     mov 0x18(%eax), %ebp
-    mov 0x1C(%eax), %ax
+    mov 0x20(%eax), %ax
     mov %ax, %ds
     mov %ax, %es
     mov %ax, %fs
     mov %ax, %gs
     pop %eax
-    iret
+    iret
+.size load_context, . - load_context

src/x86/multiboot2.c

@@ -68,6 +68,14 @@ struct multiboot2_memory_map_t
     struct multiboot2_map_entry_t entries;
 };
 
+struct multiboot2_memory_info_t
+{
+    uint32_t type;
+    uint32_t size;
+    uint32_t low_memory;
+    uint32_t high_memory;
+};
+
 void *read_multiboot_table_entry(struct boot_info_t *boot_info, void *table)
 {
     uint32_t *int_table = (uint32_t *)table;
@@ -75,6 +83,9 @@ void *read_multiboot_table_entry(struct boot_info_t *boot_info, void *table)
     {
     case MB_END_TAG:
         return NULL;
+    case MB_MEMORY_INFO:
+        boot_info->memory_size = ((struct multiboot2_memory_info_t*) table)->high_memory * 1024;
+        break;
     case MB_MEMORY_MAP: ;
         unsigned int tag_size = ((struct multiboot2_memory_map_t*) table)->size - 16;
         unsigned int entry_size = ((struct multiboot2_memory_map_t*) table)->entry_size;

src/x86/preempt.S

@@ -58,14 +58,14 @@ isr_preempt:
     mov 4(%ebp), %eax
     push %eax
 
-    // Load ESP, then push it onto stack
-    mov 12(%ebp), %eax
-    push %eax
-
     // Load SS, then push it onto stack
     mov 16(%ebp), %eax
     push %eax
 
+    // Load ESP, then push it onto stack
+    mov 12(%ebp), %eax
+    push %eax
+
     // Load EBP, then push it onto stack
     mov -4(%ebp), %eax
     push %eax
@@ -84,7 +84,7 @@ isr_preempt:
     // Push pointer to the process context saved on the stack
     push %esp
 
-    call save_context
+    call kernel_store_active_context
     mov %ebp, %esp
 
     call kernel_advance_scheduler