https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107846
--- Comment #1 from David Faust <david.faust at oracle dot com> ---
I think this is a bug in the test itself (or with these macros from libbpf).
libbpf/src/bpf_endian.h
#define ___bpf_mvb(x, b, n, m) ((__u##b)(x) << (b-(n+1)*8) >> (b-8) << (m*8))
#define ___bpf_swab16(x) ((__u16)( \
___bpf_mvb(x, 16, 0, 1) | \
___bpf_mvb(x, 16, 1, 0)))
# define __bpf_constant_htons(x) ___bpf_swab16(x)
In tools/testing/selftests/bpf/progs/test_tc_tunnel.c:
static const int cfg_port = 8000;
static const int cfg_udp_src = 20000;
...
then at e.g. line 276
if (tcph.dest != __bpf_constant_htons(cfg_port))
return TC_ACT_OK;
Expanding this __bpf_constant_htons macro:
__bpf_constant_htons (cfg_port)
__bpf_constant_htons (8000)
((__u16)(8000) << (16-(0+1)*8) >> (16-8) << (1*8)
((__u16)(8000) << (16-(1)*8) >> (8) << 8)
((__u16)(8000) << (8) >> 8 << 8
((__u16)(8000) << 8)
...which raises the shift-overflow warning.
