On 8/28/23 12:26 AM, Alan Maguire wrote:
On 26/08/2023 21:08, Yonghong Song wrote:With latest clang18, I hit test_progs failures for the following test: #13/2 bpf_cookie/multi_kprobe_link_api:FAIL #13/3 bpf_cookie/multi_kprobe_attach_api:FAIL #13 bpf_cookie:FAIL #75 fentry_fexit:FAIL #76/1 fentry_test/fentry:FAIL #76 fentry_test:FAIL #80/1 fexit_test/fexit:FAIL #80 fexit_test:FAIL #110/1 kprobe_multi_test/skel_api:FAIL #110/2 kprobe_multi_test/link_api_addrs:FAIL #110/3 kprobe_multi_test/link_api_syms:FAIL #110/4 kprobe_multi_test/attach_api_pattern:FAIL #110/5 kprobe_multi_test/attach_api_addrs:FAIL #110/6 kprobe_multi_test/attach_api_syms:FAIL #110 kprobe_multi_test:FAIL For example, for #13/2, the error messages are ... kprobe_multi_test_run:FAIL:kprobe_test7_result unexpected kprobe_test7_result: actual 0 != expected 1 ... kprobe_multi_test_run:FAIL:kretprobe_test7_result unexpected kretprobe_test7_result: actual 0 != expected 1 clang17 does not have this issue. Further investigation shows that kernel func bpf_fentry_test7(), used in the above tests, is inlined by the compiler although it is marked as noinline. int noinline bpf_fentry_test7(struct bpf_fentry_test_t *arg) { return (long)arg; } It is known that for simple functions like the above (e.g. just returning a constant or an input argument), the clang compiler may still do inlining for a noinline function. Adding 'asm volatile ("")' in the beginning of the bpf_fentry_test7() can prevent inlining. Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>Fixes: d923021c2ce12 ("bpf: Add tests for PTR_TO_BTF_ID vs. null comparison") ...might help this land in stable trees too. Thanks!
I didn't put a Fixes tag since the issue is caused by upgrading clang compiler. The commit d923021c2ce12 does not have any issues at its patch-applying time. Since this is not a core kernel functionality bug and it is due to upgrading clang compiler, I think backport is optional. But if maintainers think I should add Fixes tag, I can do it in the next revision.
--- net/bpf/test_run.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 57a7a64b84ed..0841f8d82419 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -543,6 +543,7 @@ struct bpf_fentry_test_t {int noinline bpf_fentry_test7(struct bpf_fentry_test_t *arg){ + asm volatile (""); return (long)arg; }Is there a risk bpf_fentry_test8/9 might get inlined too?
So far, not. I cannot predict in the future. But if this happens with more complicated expressions got inlined for a non-inline function, I can discuss with upstream.
