From: Willy Tarreau <w@1wt.eu>
Date: Wed, 2 Apr 2025 14:07:31 +0000 (+0200)
Subject: BUILD: quic_sock: address a strict-aliasing build warning with gcc 5 and 6
X-Git-Tag: v3.2-dev9~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dd900aead8613af12ea23b18a3e77d28ad42729b;p=thirdparty%2Fhaproxy.git

BUILD: quic_sock: address a strict-aliasing build warning with gcc 5 and 6

The UDP GSO code emits a build warning with older toolchains (gcc 5 and 6):

  src/quic_sock.c: In function 'cmsg_set_gso':
  src/quic_sock.c:683:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
    *((uint16_t *)CMSG_DATA(c)) = gso_size;
    ^

Let's just use the write_u16() function that's made for this purpose.
It was verified that for all versions from 5 to 13, gcc produces the
exact same code with the fix (and without the warning). It arrived in
3.1 with commit 448d3d388a ("MINOR: quic: add GSO parameter on quic_sock
send API") so this can be backported there.
---

diff --git a/src/quic_sock.c b/src/quic_sock.c
index b7ee8f8f4..1da0743f1 100644
--- a/src/quic_sock.c
+++ b/src/quic_sock.c
@@ -680,7 +680,7 @@ static void cmsg_set_gso(struct msghdr *msg, struct cmsghdr **cmsg,
 	c->cmsg_level = SOL_UDP;
 	c->cmsg_type = UDP_SEGMENT;
 	c->cmsg_len = CMSG_LEN(sz);
-	*((uint16_t *)CMSG_DATA(c)) = gso_size;
+	write_u16(CMSG_DATA(c), gso_size);
 #endif
 }