when -s is passed, print time, instret, cycle, and CPI

pk/boot.h

@@ -20,7 +20,9 @@ typedef struct {
   size_t brk_max;
   size_t mmap_max;
   size_t stack_top;
-  size_t t0;
+  size_t time0;
+  size_t cycle0;
+  size_t instret0;
 } elf_info;
 
 extern elf_info current;

pk/pk.c

@@ -13,7 +13,7 @@ static void handle_option(const char* s)
   switch (s[1])
   {
     case 's': // print cycle count upon termination
-      current.t0 = 1;
+      current.cycle0 = 1;
       break;
 
     default:
@@ -105,8 +105,11 @@ static void run_loaded_program(size_t argc, char** argv, uintptr_t kstack_top)
 
   STACK_INIT(uintptr_t);
 
-  if (current.t0) // start timer if so requested
-    current.t0 = rdcycle();
+  if (current.cycle0) { // start timer if so requested
+    current.time0 = rdtime();
+    current.cycle0 = rdcycle();
+    current.instret0 = rdinstret();
+  }
 
   trapframe_t tf;
   init_tf(&tf, current.entry, stack_top);

pk/syscall.c

@@ -15,8 +15,16 @@ typedef long (*syscall_t)(long, long, long, long, long, long, long);
 
 void sys_exit(int code)
 {
-  if (current.t0)
-    printk("%ld cycles\n", rdcycle() - current.t0);
+  if (current.cycle0) {
+    size_t dt = rdtime() - current.time0;
+    size_t dc = rdcycle() - current.cycle0;
+    size_t di = rdinstret() - current.instret0;
+
+    printk("%ld ticks\n", dt);
+    printk("%ld cycles\n", dc);
+    printk("%ld instructions\n", di);
+    printk("%d.%d%d CPI\n", dc/di, 10ULL*dc/di % 10, (100ULL*dc + di/2)/di % 10);
+  }
   shutdown(code);
 }