On Fri, 2024-08-30 at 02:51 -0700, Tony Ambardar wrote:
> The pahole master branch recently added support for "distilled BTF" based
> on libbpf v1.5, but may add .BTF and .BTF.base sections with the wrong byte
> order (e.g. on s390x BPF CI), which then lead to kernel Oops when loaded.
>
> Fix by updating libbpf's btf__distill_base() and btf_new_empty() to retain
> the byte order of any source BTF objects when creating new ones.
>
> Reported-by: Song Liu <song@xxxxxxxxxx>
> Reported-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Suggested-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Link: https://lore.kernel.org/bpf/6358db36c5f68b07873a0a5be2d062b1af5ea5f8.camel@xxxxxxxxx/
> Signed-off-by: Tony Ambardar <tony.ambardar@xxxxxxxxx>
> ---
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
But we also need a test for this. Like the one attached.
Or Alan can share his test, which is much shorter but skips round trip to bytes and back.
[...]
From 30fd46e4c84ba90627b039b1e721449ca8b656ad Mon Sep 17 00:00:00 2001
From: Eduard Zingerman <eddyz87@xxxxxxxxx>
Date: Fri, 30 Aug 2024 04:08:44 -0700
Subject: [PATCH bpf-next] selftests/bpf: checl if distilled base inherits
source endianness
Create a BTF with endianness different from host, make a distilled
base/split BTF pair from it, dump as raw bytes, import again and
verify that endianness is preserved.
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
.../selftests/bpf/prog_tests/btf_distill.c | 73 +++++++++++++++++++
1 file changed, 73 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/btf_distill.c b/tools/testing/selftests/bpf/prog_tests/btf_distill.c
index bfbe795823a2..810b2e434562 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_distill.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_distill.c
@@ -535,6 +535,77 @@ static void test_distilled_base_vmlinux(void)
btf__free(vmlinux_btf);
}
+static bool is_host_big_endian(void)
+{
+ return htons(0x1234) == 0x1234;
+}
+
+/* Split and new base BTFs should inherit endianness from source BTF. */
+static void test_distilled_endianness(void)
+{
+ struct btf *base = NULL, *split = NULL, *new_base = NULL, *new_split = NULL;
+ struct btf *new_base1 = NULL, *new_split1 = NULL;
+ enum btf_endianness inverse_endianness;
+ const void *raw_data;
+ __u32 size;
+
+ printf("is_host_big_endian? %d\n", is_host_big_endian());
+ inverse_endianness = is_host_big_endian() ? BTF_LITTLE_ENDIAN : BTF_BIG_ENDIAN;
+ base = btf__new_empty();
+ btf__set_endianness(base, inverse_endianness);
+ if (!ASSERT_OK_PTR(base, "empty_main_btf"))
+ return;
+ btf__add_int(base, "int", 4, BTF_INT_SIGNED); /* [1] int */
+ VALIDATE_RAW_BTF(
+ base,
+ "[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED");
+ split = btf__new_empty_split(base);
+ if (!ASSERT_OK_PTR(split, "empty_split_btf"))
+ goto cleanup;
+ btf__add_ptr(split, 1);
+ VALIDATE_RAW_BTF(
+ split,
+ "[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+ "[2] PTR '(anon)' type_id=1");
+ if (!ASSERT_EQ(0, btf__distill_base(split, &new_base, &new_split),
+ "distilled_base") ||
+ !ASSERT_OK_PTR(new_base, "distilled_base") ||
+ !ASSERT_OK_PTR(new_split, "distilled_split") ||
+ !ASSERT_EQ(2, btf__type_cnt(new_base), "distilled_base_type_cnt"))
+ goto cleanup;
+ VALIDATE_RAW_BTF(
+ new_split,
+ "[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+ "[2] PTR '(anon)' type_id=1");
+
+ raw_data = btf__raw_data(new_base, &size);
+ if (!ASSERT_OK_PTR(raw_data, "btf__raw_data #1"))
+ goto cleanup;
+ new_base1 = btf__new(raw_data, size);
+ if (!ASSERT_OK_PTR(new_base1, "new_base1 = btf__new()"))
+ goto cleanup;
+ raw_data = btf__raw_data(new_split, &size);
+ if (!ASSERT_OK_PTR(raw_data, "btf__raw_data #2"))
+ goto cleanup;
+ new_split1 = btf__new_split(raw_data, size, new_base1);
+ if (!ASSERT_OK_PTR(new_split1, "new_split1 = btf__new()"))
+ goto cleanup;
+
+ ASSERT_EQ(btf__endianness(new_base1), inverse_endianness, "new_base1 endianness");
+ ASSERT_EQ(btf__endianness(new_split1), inverse_endianness, "new_split1 endianness");
+ VALIDATE_RAW_BTF(
+ new_split1,
+ "[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+ "[2] PTR '(anon)' type_id=1");
+cleanup:
+ btf__free(new_split1);
+ btf__free(new_base1);
+ btf__free(new_split);
+ btf__free(new_base);
+ btf__free(split);
+ btf__free(base);
+}
+
void test_btf_distill(void)
{
if (test__start_subtest("distilled_base"))
@@ -549,4 +620,6 @@ void test_btf_distill(void)
test_distilled_base_multi_err2();
if (test__start_subtest("distilled_base_vmlinux"))
test_distilled_base_vmlinux();
+ if (test__start_subtest("distilled_endianness"))
+ test_distilled_endianness();
}
--
2.46.0
