On Fri, 24 Sep 2021, Yonghong Song wrote:
> With clang build kernel (adding LLVM=1 to kernel and selftests/bpf build
> command line), I hit the following test failure:
>
> $ ./test_progs -t btf_dump
> ...
> btf_dump_data:PASS:ensure expected/actual match 0 nsec
> btf_dump_data:FAIL:find type id unexpected find type id: actual -2 < expected 0
> btf_dump_data:FAIL:find type id unexpected find type id: actual -2 < expected 0
> test_btf_dump_int_data:FAIL:dump __int128 unexpected error: -2 (errno 2)
> #15/9 btf_dump/btf_dump: int_data:FAIL
>
> Further analysis showed gcc build kernel has type "__int128" in dwarf/BTF
> and it doesn't exist in clang build kernel. Code searching for kernel code
> found the following:
> arch/s390/include/asm/types.h: unsigned __int128 pair;
> crypto/ecc.c: unsigned __int128 m = (unsigned __int128)left * right;
> include/linux/math64.h: return (u64)(((unsigned __int128)a * mul) >> shift);
> include/linux/math64.h: return (u64)(((unsigned __int128)a * mul) >> shift);
> lib/ubsan.h:typedef __int128 s_max;
> lib/ubsan.h:typedef unsigned __int128 u_max;
>
> In my case, CONFIG_UBSAN is not enabled. Even if we only have "unsigned __int128"
> in the code, somehow gcc still put "__int128" in dwarf while clang didn't.
> Hence current test works fine for gcc but not for clang.
>
> Enabling CONFIG_UBSAN is an option to provide __int128 type into dwarf
> reliably for both gcc and clang, but not everybody enables CONFIG_UBSAN
> in their kernel build. So the best choice is to use "unsigned __int128" type
> which is available in both clang and gcc build kernels. But clang and gcc
> dwarf encoded names for "unsigned __int128" are different:
>
> [$ ~] cat t.c
> unsigned __int128 a;
> [$ ~] gcc -g -c t.c && llvm-dwarfdump t.o | grep __int128
> DW_AT_type (0x00000031 "__int128 unsigned")
> DW_AT_name ("__int128 unsigned")
> [$ ~] clang -g -c t.c && llvm-dwarfdump t.o | grep __int128
> DW_AT_type (0x00000033 "unsigned __int128")
> DW_AT_name ("unsigned __int128")
>
> The test change in this patch tries to test type name before
> doing actual test.
>
Thanks for finding and fixing this!
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> .../selftests/bpf/prog_tests/btf_dump.c | 27 ++++++++++++++-----
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/btf_dump.c b/tools/testing/selftests/bpf/prog_tests/btf_dump.c
> index 52ccf0cf35e1..87f9df653e4e 100644
> --- a/tools/testing/selftests/bpf/prog_tests/btf_dump.c
> +++ b/tools/testing/selftests/bpf/prog_tests/btf_dump.c
> @@ -358,12 +358,27 @@ static void test_btf_dump_int_data(struct btf *btf, struct btf_dump *d,
> TEST_BTF_DUMP_DATA_OVER(btf, d, NULL, str, int, sizeof(int)-1, "", 1);
>
> #ifdef __SIZEOF_INT128__
> - TEST_BTF_DUMP_DATA(btf, d, NULL, str, __int128, BTF_F_COMPACT,
> - "(__int128)0xffffffffffffffff",
> - 0xffffffffffffffff);
> - ASSERT_OK(btf_dump_data(btf, d, "__int128", NULL, 0, &i, 16, str,
> - "(__int128)0xfffffffffffffffffffffffffffffffe"),
> - "dump __int128");
> + /* gcc encode unsigned __int128 type with name "__int128 unsigned" in dwarf,
> + * and clang encode it with name "unsigned __int128" in dwarf.
> + * Do an availability test for either variant before doing actual test.
> + */
> + if (btf__find_by_name(btf, "unsigned __int128") > 0) {
> + TEST_BTF_DUMP_DATA(btf, d, NULL, str, unsigned __int128, BTF_F_COMPACT,
> + "(unsigned __int128)0xffffffffffffffff",
> + 0xffffffffffffffff);
> + ASSERT_OK(btf_dump_data(btf, d, "unsigned __int128", NULL, 0, &i, 16, str,
> + "(unsigned __int128)0xfffffffffffffffffffffffffffffffe"),
> + "dump unsigned __int128");
> + } else if (btf__find_by_name(btf, "__int128 unsigned") > 0) {
> + TEST_BTF_DUMP_DATA(btf, d, NULL, str, __int128 unsigned, BTF_F_COMPACT,
> + "(__int128 unsigned)0xffffffffffffffff",
> + 0xffffffffffffffff);
> + ASSERT_OK(btf_dump_data(btf, d, "__int128 unsigned", NULL, 0, &i, 16, str,
> + "(__int128 unsigned)0xfffffffffffffffffffffffffffffffe"),
> + "dump unsigned __int128");
> + } else {
> + ASSERT_TRUE(false, "unsigned_int128_not_found");
> + }
> #endif
> }
>
> --
> 2.30.2
>
>
