Moved PCB for each process to kernel heap

src/x86/preempt.S

@@ -25,14 +25,63 @@ isr_syscall:
 .global isr_preempt
 .type isr_preempt, @function
 isr_preempt:
+
+    // Disable interrupts for now
     cli
+
+    // Save process's base pointer
+    push %ebp
+
+    // Save base pointer; it points to the interrupt stack frame
+    mov %esp, %ebp
+    sub $4, %ebp
+
+    // Save EAX on stack so it can be used as a buffer
+    push %eax
+
+    // Load EFLAGS, then push it onto stack
+    mov 8(%ebp), %eax
+    push %eax
+
+    // Load EIP, then push it onto stack
+    mov 16(%ebp), %eax
+    push %eax
+
+    // Load CS, then push it onto stack
+    mov 12(%ebp), %eax
+    push %eax
+
+    // Load ESP, then push it onto stack
+    mov 4(%ebp), %eax
+    push %eax
+
+    // Load SS, then push it onto stack
+    mov (%ebp), %eax
+    push %eax
+
+    // Load EBP, then push it onto stack
+    mov -4(%ebp), %eax
+    push %eax
+
+    // Push GP registers onto stack
+    push %esi
+    push %edi
+    push %edx
+    push %ecx
+    push %ebx
+
+    // Restore saved value of EAX, then push it onto stack
+    mov -8(%ebp), %eax
+    push %eax
+
+    // Push pointer to the process context saved on the stack
     push %esp
-    push $0x800
+
     call save_context
-    add $8, %esp
-    push $0x800
+    mov %ebp, %esp
+
     call next_process
-    add $8, %esp
+
     push %eax
     call load_context