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selftests/bpf: Fix btf_dump __int128 test failure with clang build kernel

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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.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20210924025856.2192476-1-yhs@fb.com
This commit is contained in:
Yonghong Song 2021-09-23 19:58:56 -07:00 committed by Andrii Nakryiko
parent c86216bc96
commit 091037fb77
1 changed files with 21 additions and 6 deletions
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27
tools/testing/selftests/bpf/prog_tests/btf_dump.c
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@ -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
}