fix: fix segfault when loading module and improve send_buffer size calculation

kernel/kmod.c

@@ -16,7 +16,7 @@
 #define CLASS_NAME "sibyl_class"
 
 #define SLOTS 4
-#define SLOT_INTERVAL_NS 1000000000
+#define SLOT_INTERVAL_NS 100000000
 
 #define MAX_MEASUREMENTS 16
 
@@ -73,25 +73,33 @@ static uint32_t calculate_crc32(const packet_t *packet) {
 static void prepare_for_sending(void) {
   packet->crc = calculate_crc32(packet);
 
+  size_t n = 0;
+
   secondary_send_buffer[0] = packet->magic;
   secondary_send_buffer[1] = packet->data.sender_id;
   secondary_send_buffer[2] = packet->data.count;
 
-  uint8_t *bytes = (uint8_t *)packet->data.measurements;
+  n += 3;
+
+  for (size_t a = 0; a < packet->data.count; a++) {
+    uint8_t *bytes = (uint8_t *)&(packet->data.measurements[a]);
+
+    for (size_t b = 0; b < sizeof(measurement_t); b++) {
+      secondary_send_buffer[n + b] = bytes[b];
+    }
 
-  for (size_t i = 0; i < sizeof(measurement_t) * packet->data.count; i++) {
-    secondary_send_buffer[3 + i] = bytes[i];
+    n += sizeof(measurement_t);
   }
 
-  bytes = (uint8_t *)&packet->crc;
+  uint8_t *bytes = (uint8_t *)&packet->crc;
 
   for (size_t i = 0; i < sizeof(uint32_t); i++) {
-    secondary_send_buffer[3 + sizeof(measurement_t) * packet->data.count + i] =
-        bytes[i];
+    secondary_send_buffer[n + i] = bytes[i];
   }
 
-  secondary_send_buffer_size =
-      3 + sizeof(measurement_t) * packet->data.count + sizeof(uint32_t);
+  n += sizeof(uint32_t);
+
+  secondary_send_buffer_size = n;
 
   // Swap buffers
   mutex_lock(&send_buffer_mutex);
@@ -220,8 +228,6 @@ static int __init lkm_init(void) {
     return -EFAULT;
   }
 
-  prepare_for_sending();
-
   // Allocate memory for send buffers
   primary_send_buffer = (uint8_t *)vmalloc(SEND_BUFFER_SIZE);
   primary_send_buffer_size = 0;
@@ -240,6 +246,8 @@ static int __init lkm_init(void) {
     return -EFAULT;
   }
 
+  prepare_for_sending();
+
   if (alloc_chrdev_region(&dev, 0, 1, DEVICE_NAME) < 0) {
     vfree(primary_send_buffer);
     vfree(secondary_send_buffer);
@@ -325,6 +333,12 @@ static int __init lkm_init(void) {
 }
 
 static void __exit lkm_exit(void) {
+  if (timed_thread) {
+    kthread_stop(timed_thread);
+  }
+
+  hrtimer_cancel(&timer);
+
   mutex_destroy(&send_buffer_mutex);
 
   vfree(primary_send_buffer);
@@ -339,12 +353,6 @@ static void __exit lkm_exit(void) {
 
   gpio_set_value(GPIO_PIN, 0);
   gpio_free(GPIO_PIN);
-
-  if (timed_thread) {
-    kthread_stop(timed_thread);
-  }
-
-  hrtimer_cancel(&timer);
 }
 
 module_init(lkm_init);