[PATCH AUTOSEL 6.7 031/108] bpf: Fix a few selftest failures due to llvm18 change

Sasha Levin
2024-01-16T19:43:49Z

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 c9fdcc5cdce1..711cf5d59816 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -542,7 +542,7 @@ 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;
}

--
2.43.0