From: Yonghong Song yonghong.song@linux.dev

[ Upstream commit b16904fd9f01b580db357ef2b1cc9e86d89576c2 ]

With latest upstream llvm18, the following test cases failed:

$ ./test_progs -j #13/2 bpf_cookie/multi_kprobe_link_api:FAIL #13/3 bpf_cookie/multi_kprobe_attach_api:FAIL #13 bpf_cookie:FAIL #77 fentry_fexit:FAIL #78/1 fentry_test/fentry:FAIL #78 fentry_test:FAIL #82/1 fexit_test/fexit:FAIL #82 fexit_test:FAIL #112/1 kprobe_multi_test/skel_api:FAIL #112/2 kprobe_multi_test/link_api_addrs:FAIL [...] #112 kprobe_multi_test:FAIL #356/17 test_global_funcs/global_func17:FAIL #356 test_global_funcs:FAIL

Further analysis shows llvm upstream patch [1] is responsible for the above failures. For example, for function bpf_fentry_test7() in net/bpf/test_run.c, without [1], the asm code is:

0000000000000400 <bpf_fentry_test7>: 400: f3 0f 1e fa endbr64 404: e8 00 00 00 00 callq 0x409 <bpf_fentry_test7+0x9> 409: 48 89 f8 movq %rdi, %rax 40c: c3 retq 40d: 0f 1f 00 nopl (%rax)

... and with [1], the asm code is:

0000000000005d20 <bpf_fentry_test7.specialized.1>: 5d20: e8 00 00 00 00 callq 0x5d25 <bpf_fentry_test7.specialized.1+0x5> 5d25: c3 retq

... and <bpf_fentry_test7.specialized.1> is called instead of <bpf_fentry_test7> and this caused test failures for #13/#77 etc. except #356.

For test case #356/17, with [1] (progs/test_global_func17.c)), the main prog looks like:

0000000000000000 <global_func17>: 0: b4 00 00 00 2a 00 00 00 w0 = 0x2a 1: 95 00 00 00 00 00 00 00 exit

... which passed verification while the test itself expects a verification failure.

Let us add 'barrier_var' style asm code in both places to prevent function specialization which caused selftests failure.

[1] https://github.com/llvm/llvm-project/pull/72903

Signed-off-by: Yonghong Song yonghong.song@linux.dev Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20231127050342.1945270-1-yonghong.song@linux.dev Signed-off-by: Sasha Levin sashal@kernel.org --- net/bpf/test_run.c | 2 +- tools/testing/selftests/bpf/progs/test_global_func17.c | 1 + 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 0841f8d82419..478ee7aba85f 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -543,7 +543,7 @@ struct bpf_fentry_test_t {

int noinline bpf_fentry_test7(struct bpf_fentry_test_t *arg) { - asm volatile (""); + asm volatile ("": "+r"(arg)); return (long)arg; }

diff --git a/tools/testing/selftests/bpf/progs/test_global_func17.c b/tools/testing/selftests/bpf/progs/test_global_func17.c index a32e11c7d933..5de44b09e8ec 100644 --- a/tools/testing/selftests/bpf/progs/test_global_func17.c +++ b/tools/testing/selftests/bpf/progs/test_global_func17.c @@ -5,6 +5,7 @@

__noinline int foo(int *p) { + barrier_var(p); return p ? (*p = 42) : 0; }