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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 Borkmann <daniel@iogearbox.net>,
	Yonghong Song <yhs@fb.com>, Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH bpf-next 01/10] libbpf: add .BTF.ext offset relocation section loading
Date: Mon, 29 Jul 2019 20:00:41 +0000	[thread overview]
Message-ID: <A98A432B-1A26-461F-BC9B-3B72FCF8EE2B@fb.com> (raw)
In-Reply-To: <CAEf4BzYgyAiPt0wVESrWSJ_tLheq0BRWLgrqMfLZsnp11+F77Q@mail.gmail.com>



> On Jul 26, 2019, at 10:11 PM, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> 
> On Wed, Jul 24, 2019 at 10:20 PM Song Liu <songliubraving@fb.com> wrote:
>> 
>> 
>> 
>>> On Jul 24, 2019, at 5:37 PM, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>>> 
>>> On Wed, Jul 24, 2019 at 5:00 PM Song Liu <songliubraving@fb.com> wrote:
>>>> 
>>>> 
>>>> 
>>>>> On Jul 24, 2019, at 12:27 PM, Andrii Nakryiko <andriin@fb.com> wrote:
>>>>> 
>>>>> Add support for BPF CO-RE offset relocations. Add section/record
>>>>> iteration macros for .BTF.ext. These macro are useful for iterating over
>>>>> each .BTF.ext record, either for dumping out contents or later for BPF
>>>>> CO-RE relocation handling.
>>>>> 
>>>>> To enable other parts of libbpf to work with .BTF.ext contents, moved
>>>>> a bunch of type definitions into libbpf_internal.h.
>>>>> 
>>>>> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>>>>> ---
>>>>> tools/lib/bpf/btf.c             | 64 +++++++++--------------
>>>>> tools/lib/bpf/btf.h             |  4 ++
>>>>> tools/lib/bpf/libbpf_internal.h | 91 +++++++++++++++++++++++++++++++++
>>>>> 3 files changed, 118 insertions(+), 41 deletions(-)
>>>>> 
>>> 
>>> [...]
>>> 
>>>>> +
>>>>> static int btf_ext_parse_hdr(__u8 *data, __u32 data_size)
>>>>> {
>>>>>     const struct btf_ext_header *hdr = (struct btf_ext_header *)data;
>>>>> @@ -1004,6 +979,13 @@ struct btf_ext *btf_ext__new(__u8 *data, __u32 size)
>>>>>     if (err)
>>>>>             goto done;
>>>>> 
>>>>> +     /* check if there is offset_reloc_off/offset_reloc_len fields */
>>>>> +     if (btf_ext->hdr->hdr_len < sizeof(struct btf_ext_header))
>>>> 
>>>> This check will break when we add more optional sections to btf_ext_header.
>>>> Maybe use offsetof() instead?
>>> 
>>> I didn't do it, because there are no fields after offset_reloc_len.
>>> But now I though that maybe it would be ok to add zero-sized marker
>>> field, kind of like marking off various versions of btf_ext header?
>>> 
>>> Alternatively, I can add offsetofend() macro somewhere in libbpf_internal.h.
>>> 
>>> Do you have any preference?
>> 
>> We only need a stable number to compare against. offsetofend() works.
>> Or we can simply have something like
>> 
>>    if (btf_ext->hdr->hdr_len <= offsetof(struct btf_ext_header, offset_reloc_off))
>>          goto done;
>> or
>>    if (btf_ext->hdr->hdr_len < offsetof(struct btf_ext_header, offset_reloc_len))
>>          goto done;
>> 
>> Does this make sense?
> 
> I think offsetofend() is the cleanest solution, I'll do just that.

Agreed that offsetofend() is the best. 

Song


  reply	other threads:[~2019-07-29 20:01 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-24 19:27 [PATCH bpf-next 00/10] CO-RE offset relocations Andrii Nakryiko
2019-07-24 19:27 ` [PATCH bpf-next 01/10] libbpf: add .BTF.ext offset relocation section loading Andrii Nakryiko
2019-07-24 21:42   ` Andrii Nakryiko
2019-07-25  0:00   ` Song Liu
2019-07-25  0:37     ` Andrii Nakryiko
2019-07-25  5:20       ` Song Liu
2019-07-27  5:11         ` Andrii Nakryiko
2019-07-29 20:00           ` Song Liu [this message]
2019-07-24 19:27 ` [PATCH bpf-next 02/10] libbpf: implement BPF CO-RE offset relocation algorithm Andrii Nakryiko
2019-07-25 19:32   ` Song Liu
2019-07-27  6:11     ` Andrii Nakryiko
2019-07-27 18:59       ` Song Liu
2019-07-27 19:09         ` Andrii Nakryiko
2019-07-28  0:24           ` Song Liu
2019-07-25 23:18   ` Alexei Starovoitov
2019-07-27  6:25     ` Andrii Nakryiko
2019-07-27 17:00       ` Alexei Starovoitov
2019-07-27 18:24         ` Andrii Nakryiko
2019-07-27 21:29           ` Yonghong Song
2019-07-27 21:36             ` Andrii Nakryiko
2019-07-29 19:56   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 03/10] selftests/bpf: add CO-RE relocs testing setup Andrii Nakryiko
2019-07-29 20:22   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 04/10] selftests/bpf: add CO-RE relocs struct flavors tests Andrii Nakryiko
2019-07-29 20:37   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 05/10] selftests/bpf: add CO-RE relocs nesting tests Andrii Nakryiko
2019-07-29 21:06   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 06/10] selftests/bpf: add CO-RE relocs array tests Andrii Nakryiko
2019-07-25 23:26   ` Alexei Starovoitov
2019-07-26 23:29     ` Andrii Nakryiko
2019-07-24 19:27 ` [PATCH bpf-next 07/10] selftests/bpf: add CO-RE relocs enum/ptr/func_proto tests Andrii Nakryiko
2019-07-29 21:09   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 08/10] selftests/bpf: add CO-RE relocs modifiers/typedef tests Andrii Nakryiko
2019-07-29 21:11   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 09/10] selftest/bpf: add CO-RE relocs ptr-as-array tests Andrii Nakryiko
2019-07-29 21:14   ` Song Liu
2019-07-24 19:27 ` [PATCH bpf-next 10/10] selftests/bpf: add CO-RE relocs ints tests Andrii Nakryiko
2019-07-29 21:21   ` Song Liu
2019-07-29 20:20 ` [PATCH bpf-next 00/10] CO-RE offset relocations Song Liu
2019-07-29 20:36   ` Song Liu
2019-07-29 23:09     ` Andrii Nakryiko
2019-07-30  5:27       ` Song Liu

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