selftests/bpf: Avoid skipping certain subtests

Commit 704c91e ('selftests/bpf: Test "bpftool gen min_core_btf"')
added a test test_core_btfgen to test core relocation with btf
generated with 'bpftool gen min_core_btf'. Currently,
among 76 subtests, 25 are skipped.

  ...
  #46/69   core_reloc_btfgen/enumval:OK
  #46/70   core_reloc_btfgen/enumval___diff:OK
  #46/71   core_reloc_btfgen/enumval___val3_missing:OK
  #46/72   core_reloc_btfgen/enumval___err_missing:SKIP
  #46/73   core_reloc_btfgen/enum64val:OK
  #46/74   core_reloc_btfgen/enum64val___diff:OK
  #46/75   core_reloc_btfgen/enum64val___val3_missing:OK
  #46/76   core_reloc_btfgen/enum64val___err_missing:SKIP
  ...
  #46      core_reloc_btfgen:SKIP
  Summary: 1/51 PASSED, 25 SKIPPED, 0 FAILED

Alexei found that in the above core_reloc_btfgen/enum64val___err_missing
should not be skipped.

Currently, the core_reloc tests have some negative tests.
In Commit 704c91e, for core_reloc_btfgen, all negative tests
are skipped with the following condition
  if (!test_case->btf_src_file || test_case->fails) {
	test__skip();
	continue;
  }
This is too conservative. Negative tests do not fail
mkstemp() and run_btfgen() should not be skipped.
There are a few negative tests indeed failing run_btfgen()
and this patch added 'run_btfgen_fails' to mark these tests
so that they can be skipped for btfgen tests. With this,
we have
  ...
  #46/69   core_reloc_btfgen/enumval:OK
  #46/70   core_reloc_btfgen/enumval___diff:OK
  #46/71   core_reloc_btfgen/enumval___val3_missing:OK
  #46/72   core_reloc_btfgen/enumval___err_missing:OK
  #46/73   core_reloc_btfgen/enum64val:OK
  #46/74   core_reloc_btfgen/enum64val___diff:OK
  #46/75   core_reloc_btfgen/enum64val___val3_missing:OK
  #46/76   core_reloc_btfgen/enum64val___err_missing:OK
  ...
  Summary: 1/62 PASSED, 14 SKIPPED, 0 FAILED

Totally 14 subtests are skipped instead of 25.

Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>

Author: yonghong-song

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

@@ -84,6 +84,7 @@ static int duration = 0;
 #define NESTING_ERR_CASE(name) {					\
 	NESTING_CASE_COMMON(name),					\
 	.fails = true,							\
+	.run_btfgen_fails = true,							\
 }
 
 #define ARRAYS_DATA(struct_name) STRUCT_TO_CHAR_PTR(struct_name) {	\
@@ -258,12 +259,14 @@ static int duration = 0;
 	BITFIELDS_CASE_COMMON("test_core_reloc_bitfields_probed.o",	\
 			      "probed:", name),				\
 	.fails = true,							\
+	.run_btfgen_fails = true,							\
 	.raw_tp_name = "sys_enter",					\
 	.prog_name = "test_core_bitfields",				\
 }, {									\
 	BITFIELDS_CASE_COMMON("test_core_reloc_bitfields_direct.o",	\
 			      "direct:", name),				\
 	.fails = true,							\
+	.run_btfgen_fails = true,							\
 	.prog_name = "test_core_bitfields_direct",			\
 }
 
@@ -304,6 +307,7 @@ static int duration = 0;
 #define SIZE_ERR_CASE(name) {						\
 	SIZE_CASE_COMMON(name),						\
 	.fails = true,							\
+	.run_btfgen_fails = true,							\
 }
 
 #define TYPE_BASED_CASE_COMMON(name)					\
@@ -396,6 +400,7 @@ struct core_reloc_test_case {
 	const char *output;
 	int output_len;
 	bool fails;
+	bool run_btfgen_fails;
 	bool needs_testmod;
 	bool relaxed_core_relocs;
 	const char *prog_name;
@@ -952,7 +957,7 @@ static void run_core_reloc_tests(bool use_btfgen)
 		/* generate a "minimal" BTF file and use it as source */
 		if (use_btfgen) {
 
-			if (!test_case->btf_src_file || test_case->fails) {
+			if (!test_case->btf_src_file || test_case->run_btfgen_fails) {
 				test__skip();
 				continue;
 			}