On Fri, May 20, 2022 at 11:01:11AM +0200, Stefano Brivio wrote:gcc 12.1.x (e.g. current OpenSUSE Tumbleweed, x86_64 only, gcc-12-1.4.x86_64) reports: tcp.c: In function ‘tcp_send_flag’: tcp.c:1014:9: warning: writing 16 bytes into a region of size 0 [-Wstringop-overflow=] 1014 | memcpy(low_rtt_dst + hole++, &conn->a.a6, sizeof(conn->a.a6)); | ^ tcp.c:559:24: note: at offset -16 into destination object ‘low_rtt_dst’ of size 128 559 | static struct in6_addr low_rtt_dst[LOW_RTT_TABLE_SIZE]; | but 'hole' can't be -1, because the low_rtt_dst table is guaranteed to have a hole: if we happened to write to the last entry, we'll go back to index 0 and clear that one. Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>Reviewed-by: David Gibson <david(a)gibson.dropbear.id.au>--- tcp.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/tcp.c b/tcp.c index e68409a..53af3db 100644 --- a/tcp.c +++ b/tcp.c @@ -1011,6 +1011,12 @@ static void tcp_rtt_dst_check(const struct tcp_conn *conn, hole = i; } + /* Keep gcc 12 happy: this won't actually happen because the table is + * guaranteed to have a hole, see the second memcpy() below. + */ + if (hole == -1) + return; + memcpy(low_rtt_dst + hole++, &conn->a.a6, sizeof(conn->a.a6)); if (hole == LOW_RTT_TABLE_SIZE) hole = 0;-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson