selftests/bpf: fix to avoid __msg tag de-duplication by clang

__msg, __regex and __xlated tags are based on
__attribute__((btf_decl_tag("..."))) annotations.

Clang de-duplicates such annotations, e.g. the following
two sequences of tags are identical in final BTF:

/* seq A */ /* seq B */
__tag("foo") __tag("foo")
__tag("bar") __tag("bar")
__tag("foo")

Fix this by adding a unique suffix for each tag using __COUNTER__
pre-processor macro. E.g. here is a new definition for __msg:

#define __msg(msg) \
__attribute__((btf_decl_tag("comment:test_expect_msg=" XSTR(__COUNTER__) "=" msg)))

Using this definition the "seq A" from example above is translated to
BTF as follows:

[..] DECL_TAG 'comment:test_expect_msg=0=foo' type_id=X component_idx=-1
[..] DECL_TAG 'comment:test_expect_msg=1=bar' type_id=X component_idx=-1
[..] DECL_TAG 'comment:test_expect_msg=2=foo' type_id=X component_idx=-1

Surprisingly, this bug affects a single existing test:
verifier_spill_fill/old_stack_misc_vs_cur_ctx_ptr,
where sequence of identical messages was expected in the log.

Fixes: 537c3f66eac1 ("selftests/bpf: add generic BPF program tester-loader")
Signed-off-by: Eduard Zingerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/progs/bpf_misc.h

···
 #ifndef __BPF_MISC_H__
 #define __BPF_MISC_H__
 
+#define XSTR(s) STR(s)
+#define STR(s) #s
+
 /* This set of attributes controls behavior of the
  * test_loader.c:test_loader__run_subtests().
  *
···
  *                   Several __arch_* annotations could be specified at once.
  *                   When test case is not run on current arch it is marked as skipped.
  */
-#define __msg(msg)		__attribute__((btf_decl_tag("comment:test_expect_msg=" msg)))
-#define __regex(regex)		__attribute__((btf_decl_tag("comment:test_expect_regex=" regex)))
-#define __xlated(msg)		__attribute__((btf_decl_tag("comment:test_expect_xlated=" msg)))
+#define __msg(msg)		__attribute__((btf_decl_tag("comment:test_expect_msg=" XSTR(__COUNTER__) "=" msg)))
+#define __regex(regex)		__attribute__((btf_decl_tag("comment:test_expect_regex=" XSTR(__COUNTER__) "=" regex)))
+#define __xlated(msg)		__attribute__((btf_decl_tag("comment:test_expect_xlated=" XSTR(__COUNTER__) "=" msg)))
 #define __failure		__attribute__((btf_decl_tag("comment:test_expect_failure")))
 #define __success		__attribute__((btf_decl_tag("comment:test_expect_success")))
 #define __description(desc)	__attribute__((btf_decl_tag("comment:test_description=" desc)))
-#define __msg_unpriv(msg)	__attribute__((btf_decl_tag("comment:test_expect_msg_unpriv=" msg)))
-#define __regex_unpriv(regex)	__attribute__((btf_decl_tag("comment:test_expect_regex_unpriv=" regex)))
-#define __xlated_unpriv(msg)	__attribute__((btf_decl_tag("comment:test_expect_xlated_unpriv=" msg)))
+#define __msg_unpriv(msg)	__attribute__((btf_decl_tag("comment:test_expect_msg_unpriv=" XSTR(__COUNTER__) "=" msg)))
+#define __regex_unpriv(regex)	__attribute__((btf_decl_tag("comment:test_expect_regex_unpriv=" XSTR(__COUNTER__) "=" regex)))
+#define __xlated_unpriv(msg)	__attribute__((btf_decl_tag("comment:test_expect_xlated_unpriv=" XSTR(__COUNTER__) "=" msg)))
 #define __failure_unpriv	__attribute__((btf_decl_tag("comment:test_expect_failure_unpriv")))
 #define __success_unpriv	__attribute__((btf_decl_tag("comment:test_expect_success_unpriv")))
 #define __log_level(lvl)	__attribute__((btf_decl_tag("comment:test_log_level="#lvl)))

tools/testing/selftests/bpf/progs/verifier_spill_fill.c

···
  * - once for path entry - label 2;
  * - once for path entry - label 1 - label 2.
  */
-__msg("r1 = *(u64 *)(r10 -8)")
-__msg("exit")
-__msg("r1 = *(u64 *)(r10 -8)")
-__msg("exit")
+__msg("8: (79) r1 = *(u64 *)(r10 -8)")
+__msg("9: (95) exit")
+__msg("from 2 to 7")
+__msg("8: safe")
 __msg("processed 11 insns")
 __flag(BPF_F_TEST_STATE_FREQ)
 __naked void old_stack_misc_vs_cur_ctx_ptr(void)

tools/testing/selftests/bpf/test_loader.c

···
 		*flags |= flag;
 }
 
+/* Matches a string of form '<pfx>[^=]=.*' and returns it's suffix.
+ * Used to parse btf_decl_tag values.
+ * Such values require unique prefix because compiler does not add
+ * same __attribute__((btf_decl_tag(...))) twice.
+ * Test suite uses two-component tags for such cases:
+ *
+ *   <pfx> __COUNTER__ '='
+ *
+ * For example, two consecutive __msg tags '__msg("foo") __msg("foo")'
+ * would be encoded as:
+ *
+ *   [18] DECL_TAG 'comment:test_expect_msg=0=foo' type_id=15 component_idx=-1
+ *   [19] DECL_TAG 'comment:test_expect_msg=1=foo' type_id=15 component_idx=-1
+ *
+ * And the purpose of this function is to extract 'foo' from the above.
+ */
+static const char *skip_dynamic_pfx(const char *s, const char *pfx)
+{
+	const char *msg;
+
+	if (strncmp(s, pfx, strlen(pfx)) != 0)
+		return NULL;
+	msg = s + strlen(pfx);
+	msg = strchr(msg, '=');
+	if (!msg)
+		return NULL;
+	return msg + 1;
+}
+
 enum arch {
 	ARCH_X86_64	= 0x1,
 	ARCH_ARM64	= 0x2,
···
 		} else if (strcmp(s, TEST_TAG_AUXILIARY_UNPRIV) == 0) {
 			spec->auxiliary = true;
 			spec->mode_mask |= UNPRIV;
-		} else if (str_has_pfx(s, TEST_TAG_EXPECT_MSG_PFX)) {
-			msg = s + sizeof(TEST_TAG_EXPECT_MSG_PFX) - 1;
+		} else if ((msg = skip_dynamic_pfx(s, TEST_TAG_EXPECT_MSG_PFX))) {
 			err = push_msg(msg, NULL, &spec->priv.expect_msgs);
 			if (err)
 				goto cleanup;
 			spec->mode_mask |= PRIV;
-		} else if (str_has_pfx(s, TEST_TAG_EXPECT_MSG_PFX_UNPRIV)) {
-			msg = s + sizeof(TEST_TAG_EXPECT_MSG_PFX_UNPRIV) - 1;
+		} else if ((msg = skip_dynamic_pfx(s, TEST_TAG_EXPECT_MSG_PFX_UNPRIV))) {
 			err = push_msg(msg, NULL, &spec->unpriv.expect_msgs);
 			if (err)
 				goto cleanup;
 			spec->mode_mask |= UNPRIV;
-		} else if (str_has_pfx(s, TEST_TAG_EXPECT_REGEX_PFX)) {
-			msg = s + sizeof(TEST_TAG_EXPECT_REGEX_PFX) - 1;
+		} else if ((msg = skip_dynamic_pfx(s, TEST_TAG_EXPECT_REGEX_PFX))) {
 			err = push_msg(NULL, msg, &spec->priv.expect_msgs);
 			if (err)
 				goto cleanup;
 			spec->mode_mask |= PRIV;
-		} else if (str_has_pfx(s, TEST_TAG_EXPECT_REGEX_PFX_UNPRIV)) {
-			msg = s + sizeof(TEST_TAG_EXPECT_REGEX_PFX_UNPRIV) - 1;
+		} else if ((msg = skip_dynamic_pfx(s, TEST_TAG_EXPECT_REGEX_PFX_UNPRIV))) {
 			err = push_msg(NULL, msg, &spec->unpriv.expect_msgs);
 			if (err)
 				goto cleanup;
 			spec->mode_mask |= UNPRIV;
-		} else if (str_has_pfx(s, TEST_TAG_EXPECT_XLATED_PFX)) {
-			msg = s + sizeof(TEST_TAG_EXPECT_XLATED_PFX) - 1;
+		} else if ((msg = skip_dynamic_pfx(s, TEST_TAG_EXPECT_XLATED_PFX))) {
 			err = push_msg(msg, NULL, &spec->priv.expect_xlated);
 			if (err)
 				goto cleanup;
 			spec->mode_mask |= PRIV;
-		} else if (str_has_pfx(s, TEST_TAG_EXPECT_XLATED_PFX_UNPRIV)) {
-			msg = s + sizeof(TEST_TAG_EXPECT_XLATED_PFX_UNPRIV) - 1;
+		} else if ((msg = skip_dynamic_pfx(s, TEST_TAG_EXPECT_XLATED_PFX_UNPRIV))) {
 			err = push_msg(msg, NULL, &spec->unpriv.expect_xlated);
 			if (err)
 				goto cleanup;