selftests/bpf: Fix btf_dump test cases on 32-bit arches

Fix btf_dump test cases by hard-coding BPF's pointer size of 8 bytes for cases
where it's impossible to deterimne the pointer size (no long type in BTF). In
cases where it's known, validate libbpf correctly determines it as 8.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200813204945.1020225-6-andriin@fb.com

tools/testing/selftests/bpf/prog_tests/btf_dump.c

@@ -12,15 +12,16 @@ void btf_dump_printf(void *ctx, const char *fmt, va_list args)
 static struct btf_dump_test_case {
 	const char *name;
 	const char *file;
+	bool known_ptr_sz;
 	struct btf_dump_opts opts;
 } btf_dump_test_cases[] = {
-	{"btf_dump: syntax", "btf_dump_test_case_syntax", {}},
-	{"btf_dump: ordering", "btf_dump_test_case_ordering", {}},
-	{"btf_dump: padding", "btf_dump_test_case_padding", {}},
-	{"btf_dump: packing", "btf_dump_test_case_packing", {}},
-	{"btf_dump: bitfields", "btf_dump_test_case_bitfields", {}},
-	{"btf_dump: multidim", "btf_dump_test_case_multidim", {}},
-	{"btf_dump: namespacing", "btf_dump_test_case_namespacing", {}},
+	{"btf_dump: syntax", "btf_dump_test_case_syntax", true, {}},
+	{"btf_dump: ordering", "btf_dump_test_case_ordering", false, {}},
+	{"btf_dump: padding", "btf_dump_test_case_padding", true, {}},
+	{"btf_dump: packing", "btf_dump_test_case_packing", true, {}},
+	{"btf_dump: bitfields", "btf_dump_test_case_bitfields", true, {}},
+	{"btf_dump: multidim", "btf_dump_test_case_multidim", false, {}},
+	{"btf_dump: namespacing", "btf_dump_test_case_namespacing", false, {}},
 };
 
 static int btf_dump_all_types(const struct btf *btf,
@@ -62,6 +63,18 @@ static int test_btf_dump_case(int n, struct btf_dump_test_case *t)
 		goto done;
 	}
 
+	/* tests with t->known_ptr_sz have no "long" or "unsigned long" type,
+	 * so it's impossible to determine correct pointer size; but if they
+	 * do, it should be 8 regardless of host architecture, becaues BPF
+	 * target is always 64-bit
+	 */
+	if (!t->known_ptr_sz) {
+		btf__set_pointer_size(btf, 8);
+	} else {
+		CHECK(btf__pointer_size(btf) != 8, "ptr_sz", "exp %d, got %zu\n",
+		      8, btf__pointer_size(btf));
+	}
+
 	snprintf(out_file, sizeof(out_file), "/tmp/%s.output.XXXXXX", t->file);
 	fd = mkstemp(out_file);
 	if (CHECK(fd < 0, "create_tmp", "failed to create file: %d\n", fd)) {