> On Jul 24, 2019, at 5:37 PM, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Wed, Jul 24, 2019 at 5:00 PM Song Liu <songliubraving@xxxxxx> wrote:
>>
>>
>>
>>> On Jul 24, 2019, at 12:27 PM, Andrii Nakryiko <andriin@xxxxxx> 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@xxxxxx>
>>> ---
>>> 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?
Thanks,
Song
