Re: [PATCHv3 bpf-next 7/7] selftests/bpf: Add test for bpf_get_func_ip in kprobe+offset probe

On Mon, Jul 12, 2021 at 04:32:25PM -0700, Andrii Nakryiko wrote:

On Sun, Jul 11, 2021 at 7:48 AM Jiri Olsa [off-list ref] wrote:

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On Wed, Jul 07, 2021 at 05:18:49PM -0700, Andrii Nakryiko wrote:

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On Wed, Jul 7, 2021 at 2:54 PM Jiri Olsa [off-list ref] wrote:

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Adding test for bpf_get_func_ip in kprobe+ofset probe.

typo: offset

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Because of the offset value it's arch specific, adding
it only for x86_64 architecture.

I'm not following, you specified +0x5 offset explicitly, why is this
arch-specific?

I need some instruction offset != 0 in the traced function,
x86_64's fentry jump is 5 bytes, other archs will be different

Right, ok. I don't see an easy way to detect this offset, but the
#ifdef __x86_64__ detection doesn't work because we are compiling with
-target bpf. Please double-check that it actually worked in the first
place.

ugh, right

I think a better way would be to have test6 defined unconditionally in
BPF code, but then disable loading test6 program on anything but
x86_64 platform at runtime with bpf_program__set_autoload(false).

great, I did not know about this function, will be easier

thanks,
jirka

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Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 .../testing/selftests/bpf/progs/get_func_ip_test.c  | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
index 8ca54390d2b1..e8a9428a0ea3 100644
--- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c
+++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c

@@ -10,6 +10,7 @@ extern const void bpf_fentry_test2 __ksym;
 extern const void bpf_fentry_test3 __ksym;
 extern const void bpf_fentry_test4 __ksym;
 extern const void bpf_modify_return_test __ksym;
+extern const void bpf_fentry_test6 __ksym;

 __u64 test1_result = 0;
 SEC("fentry/bpf_fentry_test1")

@@ -60,3 +61,15 @@ int BPF_PROG(fmod_ret_test, int a, int *b, int ret)
        test5_result = (const void *) addr == &bpf_modify_return_test;
        return ret;
 }
+
+#ifdef __x86_64__
+__u64 test6_result = 0;

see, and you just forgot to update the user-space part of the test to
even check test6_result...

please group variables together and do explicit ASSERT_EQ

right.. will change

thanks,
jirka

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+SEC("kprobe/bpf_fentry_test6+0x5")
+int test6(struct pt_regs *ctx)
+{
+       __u64 addr = bpf_get_func_ip(ctx);
+
+       test6_result = (const void *) addr == &bpf_fentry_test6 + 5;
+       return 0;
+}
+#endif
--
2.31.1