Added functions to create and load process contexts

src/x86/context.c

@@ -0,0 +1,32 @@
+#include "context.h"
+#include "pageallocator.h"
+#include "mmgr.h"
+
+void *initialize_context(void *task_entry, struct page_stack_t *page_stack)
+{
+    physaddr_t stack0 = reserve_page(page_stack);
+    map_page(page_stack, (void*)0xFF7FF000, stack0, PAGE_RW);
+    map_page(page_stack, (void*)0xFF7FD000, stack0, PAGE_RW | PAGE_USERMODE);
+    unmap_page((void*)0xFF7FE000);
+    unmap_page((void*)0xFF7FC000);
+    uint32_t flags;
+    uint32_t *stack = (uint32_t*)((void*)stack0 - 20);
+    asm("pushf; "
+        "mov (%%esp), %0; "
+        "popf; "
+        : "=r"(flags));
+    stack[0] = (uint32_t)task_entry;
+    stack[1] = 27;
+    stack[2] = flags;
+    stack[3] = 0xFF7FE000;
+    stack[4] = 35;
+    return (void*)stack;
+}
+
+void load_context(struct process_state_t *context)
+{
+    asm("mov %0, %%esp; "
+        "popal; "
+        "iret; "
+        :: "r"(context));
+}