Fix MISRA 2012 violations

MISRA.md

@@ -22,6 +22,18 @@ with ( Assuming rule 11.4 violation; with justification in point 2 ):
 grep 'MISRA Ref 11.4.2' . -rI
 ```
 
+#### Directive 4.7
+
+_Ref 4.7.1_
+
+- MISRA C:2012 Directive 4.7: Return value shall be checked.
+  MISRA warns against not checking the return value of functions that
+  does return. However, the violations reported in FreeRTOS-Plus-TCP
+  library for this directive are for the cases where the validity of the
+  subsequent expressions are validated by ways other than return
+  value of the called function, for example pointer value
+  that was passed as argument.
+
 #### Directive 4.12
 
 _Ref 4.12.1_

source/FreeRTOS_ARP.c

@@ -926,7 +926,7 @@
                 }
             }
         }
-        else if( xIsIPv4Broadcast( ulAddressToLookup, ppxEndPoint ) )
+        else if( xIsIPv4Broadcast( ulAddressToLookup, ppxEndPoint ) == pdTRUE )
         {
             /* This is a broadcast so it uses the broadcast MAC address. */
             ( void ) memcpy( pxMACAddress->ucBytes, xBroadcastMACAddress.ucBytes, sizeof( MACAddress_t ) );

source/FreeRTOS_DHCP.c

@@ -230,6 +230,7 @@
                     }
                     else
                     {
+                        /* do nothing, coverity happy */
                     }
 
                     break;

source/FreeRTOS_DHCPv6.c

@@ -442,6 +442,7 @@ void vDHCPv6Process( BaseType_t xReset,
                 }
                 else
                 {
+                    /* do nothing, coverity happy */
                 }
 
                 break;

source/FreeRTOS_IP_Utils.c

@@ -1835,6 +1835,9 @@ void vReleaseSinglePacketFromUDPSocket( const ConstSocket_t xSocket )
     int32_t lBytes;
 
     /* Passing the address of a pointer (pucUDPPayload) because FREERTOS_ZERO_COPY is used. */
+    /* MISRA Ref 4.7.1 [Return value shall be checked] */
+    /* More details at: https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/blob/main/MISRA.md#directive-47. */
+    /* coverity[misra_c_2012_directive_4_7_violation] */
     lBytes = FreeRTOS_recvfrom( xSocket, &pucUDPPayload, 0U, FREERTOS_ZERO_COPY, NULL, NULL );
 
     ( void ) lBytes;

source/FreeRTOS_IPv4.c

@@ -253,14 +253,18 @@ BaseType_t xIsIPv4Broadcast( uint32_t ulIPAddress,
             xIsBroadcast = pdTRUE;
             break;
         }
+        else
+        {
+            /* do nothing, coverity happy */
+        }
     }
 
     /* If the caller wants to know the corresponding endpoint, copy the result.
      * Note that this may be null if ulIPAddress is 255.255.255.255 AND there are
      * no IPv4 endpoints.
      * Also, when ulIPAddress is 255.255.255.255, we will
      * return the first IPv4 endpoint that we run across. */
-    if( xIsBroadcast && ( ppxEndPoint != NULL ) )
+    if( ( xIsBroadcast == pdTRUE ) && ( ppxEndPoint != NULL ) )
     {
         *ppxEndPoint = pxEndPoint;
     }
@@ -347,7 +351,7 @@ enum eFrameProcessingResult prvAllowIPPacketIPv4( const struct xIP_PACKET * cons
         uint32_t ulDestinationIPAddress = pxIPHeader->ulDestinationIPAddress;
         uint32_t ulSourceIPAddress = pxIPHeader->ulSourceIPAddress;
         /* Get a reference to the endpoint that the packet was assigned to during pxEasyFit() */
-        NetworkEndPoint_t * pxEndPoint = pxNetworkBuffer->pxEndPoint;
+        const NetworkEndPoint_t * pxEndPoint = pxNetworkBuffer->pxEndPoint;
 
         /* Ensure that the incoming packet is not fragmented because the stack
          * doesn't not support IP fragmentation. All but the last fragment coming in will have their

source/FreeRTOS_TCP_Transmission.c

@@ -1361,6 +1361,9 @@
                                        uint32_t ulCurrentSequenceNumber,
                                        uint32_t ulOurSequenceNumber )
     {
+        /* MISRA Ref 11.3.1 [Misaligned access] */
+        /* More details at: https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/blob/main/MISRA.md#rule-113 */
+        /* coverity[misra_c_2012_rule_11_3_violation] */
         ProtocolHeaders_t * pxProtocolHeaders = ( ( ProtocolHeaders_t * )
                                                   &( pxNetworkBuffer->pucEthernetBuffer[ ipSIZE_OF_ETH_HEADER + uxIPHeaderSizePacket( pxNetworkBuffer ) ] ) );