Commit 2220ecf5 authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
Browse files

selftests/bpf: Skip btf_tag test if btf_tag attribute not supported 



Commit c240ba28 ("selftests/bpf: Add a test with a bpf
program with btf_tag attributes") added btf_tag selftest
to test BTF_KIND_TAG generation from C source code, and to
test kernel validation of generated BTF types.
But if an old clang (clang 13 or earlier) is used, the
following compiler warning may be seen:
  progs/tag.c:23:20: warning: unknown attribute 'btf_tag' ignored
and the test itself is marked OK. The compiler warning is bad
and the test itself shouldn't be marked OK.

This patch added the check for btf_tag attribute support.
If btf_tag is not supported by the clang, the attribute will
not be used in the code and the test will be marked as skipped.
For example, with clang 13:
  ./test_progs -t btf_tag
  #21 btf_tag:SKIP
  Summary: 1/0 PASSED, 1 SKIPPED, 0 FAILED

The selftests/README.rst is updated to clarify when the btf_tag
test may be skipped.

Signed-off-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210915061036.2577971-1-yhs@fb.com
parent 4c24483e

tools/testing/selftests/bpf/README.rst

+14 −0
Original line number Diff line number Diff line
@@ -201,6 +201,20 @@ Without it, the error from compiling bpf selftests looks like: 


__ https://reviews.llvm.org/D93563



btf_tag test and Clang version

==============================



The btf_tag selftest require LLVM support to recognize the btf_tag attribute.

It was introduced in `Clang 14`__.



Without it, the btf_tag selftest will be skipped and you will observe:



.. code-block:: console



  #<test_num> btf_tag:SKIP



__ https://reviews.llvm.org/D106614



Clang dependencies for static linking tests

===========================================

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

+6 −0
Original line number Diff line number Diff line
@@ -10,5 +10,11 @@ void test_btf_tag(void) 
	skel = tag__open_and_load();

	if (!ASSERT_OK_PTR(skel, "btf_tag"))

		return;



	if (skel->rodata->skip_tests) {

		printf("%s:SKIP: btf_tag attribute not supported", __func__);

		test__skip();

	}



	tag__destroy(skel);

}

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

+11 −1
Original line number Diff line number Diff line
@@ -4,8 +4,19 @@ 
#include <bpf/bpf_helpers.h>

#include <bpf/bpf_tracing.h>



#ifndef __has_attribute

#define __has_attribute(x) 0

#endif



#if __has_attribute(btf_tag)

#define __tag1 __attribute__((btf_tag("tag1")))

#define __tag2 __attribute__((btf_tag("tag2")))

volatile const bool skip_tests __tag1 __tag2 = false;

#else

#define __tag1

#define __tag2

volatile const bool skip_tests = true;

#endif



struct key_t {

	int a;
@@ -20,7 +31,6 @@ struct { 
	__type(value, __u64);

} hashmap1 SEC(".maps");



__u32 total __tag1 __tag2 = 0;



static __noinline int foo(int x __tag1 __tag2) __tag1 __tag2

{