Major restructure

kern/libkern/proc.c

@@ -0,0 +1,21 @@
+#include <proc.h>
+
+struct Cpu cpus[NCPU];
+
+/**
+ * Must be called with interrupts disabled, to prevent race with process being
+ * moved to a different CPU.
+ */
+int cpuid() {
+    int id = read_tp();
+    return id;
+}
+
+/**
+ * Return this CPU's cpu struct. Interrupts must be disabled.
+ */
+struct Cpu *mycpu(void) {
+    int         id = cpuid();
+    struct Cpu *c = &cpus[id];
+    return c;
+}