Switch to using an unaligned read helper that does the reads via memcpy.

Author: resistor

include/endianness.hh

@@ -1,6 +1,7 @@
 // Copyright SCI Semiconductor and CHERIoT Contributors.
 // SPDX-License-Identifier: MIT
 
+#include "cdefs.h"
 #include <stdint.h>
 
 uint16_t constexpr ntohs(uint16_t value)
@@ -24,3 +25,11 @@ uint16_t constexpr htons(uint16_t value)
 #endif
 	    ;
 }
+
+template<class T>
+__always_inline T read_unaligned(const void *p)
+{
+	T val;
+	__builtin_memcpy(&val, p, sizeof(T));
+	return val;
+}

lib/dns/dns.cc

@@ -808,12 +808,12 @@ namespace
 		if (isIPv6)
 		{
 			queryResult.kind = NetworkAddress::AddressKindIPv6;
-			uint16_t *ipv6 = reinterpret_cast<uint16_t *>(&queryResult.ipv6[0]);
+			uint8_t *ipv6    = queryResult.ipv6;
 			// Enforce machine byte order by block of 2 byte.
 			for (int i = 0; i < 8; i++)
 			{
-				*ipv6++ = ntohs(
-				  *reinterpret_cast<uint16_t *>(dnsPacket + currentOffset));
+				*ipv6++ =
+				  ntohs(read_unaligned<uint16_t>(dnsPacket + currentOffset));
 				currentOffset += 2;
 			}
 		}
@@ -1110,15 +1110,15 @@ __cheri_compartment("DNS") int network_host_resolve(Timeout        *timeout,
 	{
 		Debug::log("Resolved {} -> {}:{}:{}:{}:{}:{}:{}:{}",
 		           hostname,
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[0]),
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[2]),
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[4]),
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[6]),
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[8]),
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[10]),
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[12]),
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[14]),
-		           *reinterpret_cast<uint16_t *>(&queryResult.ipv6[16]));
+		           read_unaligned<uint16_t>(&queryResult.ipv6[0]),
+		           read_unaligned<uint16_t>(&queryResult.ipv6[2]),
+		           read_unaligned<uint16_t>(&queryResult.ipv6[4]),
+		           read_unaligned<uint16_t>(&queryResult.ipv6[6]),
+		           read_unaligned<uint16_t>(&queryResult.ipv6[8]),
+		           read_unaligned<uint16_t>(&queryResult.ipv6[10]),
+		           read_unaligned<uint16_t>(&queryResult.ipv6[12]),
+		           read_unaligned<uint16_t>(&queryResult.ipv6[14]),
+		           read_unaligned<uint16_t>(&queryResult.ipv6[16]));
 	}
 
 	// We are now good to process the next lookup.

lib/dns/protocol-headers.hh

@@ -68,7 +68,7 @@ uint16_t compute_ipv4_checksum(const uint8_t *header, uint16_t length)
 
 	while (length > 1)
 	{
-		sum += *reinterpret_cast<const uint16_t *>(header);
+		sum += read_unaligned<uint16_t>(header);
 		header += 2;
 		length -= 2;
 	}