From: Song Liu <songliubraving@fb.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
Networking <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@fb.com>,
"daniel@iogearbox.net" <daniel@iogearbox.net>,
Yonghong Song <yhs@fb.com>, Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH v2 bpf-next 03/12] selftests/bpf: add BPF_CORE_READ relocatable read macro
Date: Tue, 30 Jul 2019 21:33:15 +0000 [thread overview]
Message-ID: <505D545B-4BAF-4278-A36F-92F455A169D1@fb.com> (raw)
In-Reply-To: <CAEf4BzakowCqkCkBdGPJCZNU3MpDf1yBhzOXL2pos1tPiUH0mQ@mail.gmail.com>
> On Jul 30, 2019, at 2:26 PM, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>
> On Tue, Jul 30, 2019 at 2:24 PM Song Liu <songliubraving@fb.com> wrote:
>>
>>
>>
>>> On Jul 30, 2019, at 12:53 PM, Andrii Nakryiko <andriin@fb.com> wrote:
>>>
>>> Add BPF_CORE_READ macro used in tests to do bpf_core_read(), which
>>> automatically captures offset relocation.
>>>
>>> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>>> ---
>>> tools/testing/selftests/bpf/bpf_helpers.h | 19 +++++++++++++++++++
>>> 1 file changed, 19 insertions(+)
>>>
>>> diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
>>> index f804f210244e..81bc51293d11 100644
>>> --- a/tools/testing/selftests/bpf/bpf_helpers.h
>>> +++ b/tools/testing/selftests/bpf/bpf_helpers.h
>>> @@ -501,4 +501,23 @@ struct pt_regs;
>>> (void *)(PT_REGS_FP(ctx) + sizeof(ip))); })
>>> #endif
>>>
>>> +/*
>>> + * BPF_CORE_READ abstracts away bpf_probe_read() call and captures offset
>>> + * relocation for source address using __builtin_preserve_access_index()
>>> + * built-in, provided by Clang.
>>> + *
>>> + * __builtin_preserve_access_index() takes as an argument an expression of
>>> + * taking an address of a field within struct/union. It makes compiler emit
>>> + * a relocation, which records BTF type ID describing root struct/union and an
>>> + * accessor string which describes exact embedded field that was used to take
>>> + * an address. See detailed description of this relocation format and
>>> + * semantics in comments to struct bpf_offset_reloc in libbpf_internal.h.
>>> + *
>>> + * This relocation allows libbpf to adjust BPF instruction to use correct
>>> + * actual field offset, based on target kernel BTF type that matches original
>>> + * (local) BTF, used to record relocation.
>>> + */
>>> +#define BPF_CORE_READ(dst, src) \
>>> + bpf_probe_read(dst, sizeof(*src), __builtin_preserve_access_index(src))
>>
>> We should use "sizeof(*(src))"
>>
>
> Good point. Also (dst) instead of just (dst). Will update.
I think dst as-is is fine. "," is the very last in precedence list.
next prev parent reply other threads:[~2019-07-30 21:34 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-30 19:53 [PATCH v2 bpf-next 00/12] CO-RE offset relocations Andrii Nakryiko
2019-07-30 19:53 ` [PATCH v2 bpf-next 01/12] libbpf: add .BTF.ext offset relocation section loading Andrii Nakryiko
2019-07-30 21:19 ` Song Liu
2019-07-30 19:53 ` [PATCH v2 bpf-next 02/12] libbpf: implement BPF CO-RE offset relocation algorithm Andrii Nakryiko
2019-07-30 23:43 ` Song Liu
2019-07-30 23:55 ` Andrii Nakryiko
2019-07-31 0:16 ` Song Liu
2019-07-31 0:39 ` Song Liu
2019-07-31 1:00 ` Andrii Nakryiko
2019-07-31 5:19 ` Song Liu
2019-07-31 6:52 ` Andrii Nakryiko
2019-07-31 8:29 ` Song Liu
2019-07-31 17:18 ` Andrii Nakryiko
2019-07-31 17:46 ` Song Liu
2019-07-30 19:53 ` [PATCH v2 bpf-next 03/12] selftests/bpf: add BPF_CORE_READ relocatable read macro Andrii Nakryiko
2019-07-30 21:24 ` Song Liu
2019-07-30 21:26 ` Andrii Nakryiko
2019-07-30 21:33 ` Song Liu [this message]
2019-07-30 19:54 ` [PATCH v2 bpf-next 04/12] selftests/bpf: add CO-RE relocs testing setup Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 05/12] selftests/bpf: add CO-RE relocs struct flavors tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 06/12] selftests/bpf: add CO-RE relocs nesting tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 07/12] selftests/bpf: add CO-RE relocs array tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 08/12] selftests/bpf: add CO-RE relocs enum/ptr/func_proto tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 09/12] selftests/bpf: add CO-RE relocs modifiers/typedef tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 10/12] selftests/bpf: add CO-RE relocs ptr-as-array tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 11/12] selftests/bpf: add CO-RE relocs ints tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 12/12] selftests/bpf: add CO-RE relocs misc tests Andrii Nakryiko
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