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?
>
> 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?
> +
> +#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
>
