passt: Address new clang-tidy warnings from LLVM 13.0.1

clang-tidy from LLVM 13.0.1 reports some new warnings from these
checkers:

- altera-unroll-loops, altera-id-dependent-backward-branch: ignore
  for the moment being, add a TODO item

- bugprone-easily-swappable-parameters: ignore, nothing to do about
  those

- readability-function-cognitive-complexity: ignore for the moment
  being, add a TODO item

- altera-struct-pack-align: ignore, alignment is forced in protocol
  headers

- concurrency-mt-unsafe: ignore for the moment being, add a TODO
  item

Fix bugprone-implicit-widening-of-multiplication-result warnings,
though, that's doable and they seem to make sense.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/checksum.c b/checksum.c
index c9905d1..acb1e3e 100644
--- a/checksum.c
+++ b/checksum.c
@@ -108,10 +108,13 @@ uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init)
  */
 void csum_tcp4(struct iphdr *iph)
 {
-	struct tcphdr *th = (struct tcphdr *)((char *)iph + iph->ihl * 4);
-	uint16_t tlen = ntohs(iph->tot_len) - iph->ihl * 4, *p = (uint16_t *)th;
+	uint16_t tlen = ntohs(iph->tot_len) - iph->ihl * 4, *p;
+	struct tcphdr *th;
 	uint32_t sum = 0;
 
+	th = (struct tcphdr *)((char *)iph + (intptr_t)(iph->ihl * 4));
+	p = (uint16_t *)th;
+
 	sum += (iph->saddr >> 16) & 0xffff;
 	sum += iph->saddr & 0xffff;
 	sum += (iph->daddr >> 16) & 0xffff;