On 11/11/21 10:55 AM, Andrii Nakryiko wrote:
On Tue, Nov 9, 2021 at 9:21 PM Yonghong Song <yhs@xxxxxx> wrote:
For the C test, compiler the kernel and selftest with clang compiler
by adding LLVM=1 to the make command line since btf_type_tag is
only supported by clang compiler now.
I'm confused. Why does kernel compilation matter at all? And then for
progs/*.c we always compile with Clang anyway (except for unused
gcc_bpf flavor, but that's separate). So what am I missing?
This patch set is tested with additional change with
#define __user __attribute__((btf_type_tag("user")))
plus pahole hack so I can ensure kernel implementation is
okay with vmlinux + btf_type_tag.
LLVM=1 is needed to test this.
But just for this patch set, you are right, LLVM=1 is not needed.
Will remove it.
The following is the key btf_type_tag usage:
#define __tag1 __attribute__((btf_type_tag("tag1")))
#define __tag2 __attribute__((btf_type_tag("tag2")))
struct btf_type_tag_test {
int __tag1 * __tag1 __tag2 *p;
} g;
The bpftool raw dump with related types:
[4] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
[11] STRUCT 'btf_type_tag_test' size=8 vlen=1
'p' type_id=14 bits_offset=0
[12] TYPE_TAG 'tag1' type_id=16
[13] TYPE_TAG 'tag2' type_id=12
[14] PTR '(anon)' type_id=13
[15] TYPE_TAG 'tag1' type_id=4
[16] PTR '(anon)' type_id=15
[17] VAR 'g' type_id=11, linkage=global
With format C dump, we have
struct btf_type_tag_test {
int __attribute__((btf_type_tag("tag1"))) * __attribute__((btf_type_tag("tag1"))) __attribute__((btf_type_tag("tag2"))) *p;
};
The result C code is identical to the original definition except macro's are gone.
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
.../selftests/bpf/prog_tests/btf_tag.c | 24 +++++++++++++++
.../selftests/bpf/progs/btf_type_tag.c | 29 +++++++++++++++++++
2 files changed, 53 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/btf_type_tag.c
diff --git a/tools/testing/selftests/bpf/prog_tests/btf_tag.c b/tools/testing/selftests/bpf/prog_tests/btf_tag.c
index d15cc7a88182..88d63e23e35f 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_tag.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_tag.c
@@ -3,6 +3,12 @@
#include <test_progs.h>
#include "btf_decl_tag.skel.h"
+/* struct btf_type_tag_test is referenced in btf_type_tag.skel.h */
+struct btf_type_tag_test {
+ int **p;
+};
+#include "btf_type_tag.skel.h"
+
static void test_btf_decl_tag(void)
{
struct btf_decl_tag *skel;
@@ -19,8 +25,26 @@ static void test_btf_decl_tag(void)
btf_decl_tag__destroy(skel);
}
+static void test_btf_type_tag(void)
+{
+ struct btf_type_tag *skel;
+
+ skel = btf_type_tag__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "btf_type_tag"))
+ return;
+
+ if (skel->rodata->skip_tests) {
+ printf("%s:SKIP: btf_type_tag attribute not supported", __func__);
+ test__skip();
+ }
+
+ btf_type_tag__destroy(skel);
+}
+
void test_btf_tag(void)
{
if (test__start_subtest("btf_decl_tag"))
test_btf_decl_tag();
+ if (test__start_subtest("btf_type_tag"))
+ test_btf_type_tag();
}
diff --git a/tools/testing/selftests/bpf/progs/btf_type_tag.c b/tools/testing/selftests/bpf/progs/btf_type_tag.c
new file mode 100644
index 000000000000..0e18c777862c
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf_type_tag.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#ifndef __has_attribute
+#define __has_attribute(x) 0
+#endif
is this necessary, doesn't the minimum Clang/GCC version that we
support have __has_attribute already?
No. It is not necessary. I just copy-pasted code from
https://clang.llvm.org/docs/LanguageExtensions.html#has-attribute
We recommend clang >= 11 for kernel. So above is indeed not
needed.
+
+#if __has_attribute(btf_type_tag)
+#define __tag1 __attribute__((btf_type_tag("tag1")))
+#define __tag2 __attribute__((btf_type_tag("tag2")))
+volatile const bool skip_tests = false;
+#else
+#define __tag1
+#define __tag2
+volatile const bool skip_tests = true;
+#endif
+
+struct btf_type_tag_test {
+ int __tag1 * __tag1 __tag2 *p;
+} g;
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(sub, int x)
+{
+ return 0;
+}
--
2.30.2
