> On Nov 10, 2020, at 10:31 AM, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Tue, Nov 10, 2020 at 9:50 AM Song Liu <songliubraving@xxxxxx> wrote:
>>
>>
>>
>>> On Nov 9, 2020, at 5:19 PM, Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>>>
>>> Adjust in-kernel BTF implementation to support a split BTF mode of operation.
>>> Changes are mostly mirroring libbpf split BTF changes, with the exception of
>>> start_id being 0 for in-kernel implementation due to simpler read-only mode.
>>>
>>> Otherwise, for split BTF logic, most of the logic of jumping to base BTF,
>>> where necessary, is encapsulated in few helper functions. Type numbering and
>>> string offset in a split BTF are logically continuing where base BTF ends, so
>>> most of the high-level logic is kept without changes.
>>>
>>> Type verification and size resolution is only doing an added resolution of new
>>> split BTF types and relies on already cached size and type resolution results
>>> in the base BTF.
>>>
>>> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
>>> ---
>>> kernel/bpf/btf.c | 171 +++++++++++++++++++++++++++++++++--------------
>>> 1 file changed, 119 insertions(+), 52 deletions(-)
>>>
>>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>>> index 6324de8c59f7..727c1c27053f 100644
>>> --- a/kernel/bpf/btf.c
>>> +++ b/kernel/bpf/btf.c
>>> @@ -203,12 +203,17 @@ struct btf {
>>> const char *strings;
>>> void *nohdr_data;
>>> struct btf_header hdr;
>>> - u32 nr_types;
>>> + u32 nr_types; /* includes VOID for base BTF */
>>> u32 types_size;
>>> u32 data_size;
>>> refcount_t refcnt;
>>> u32 id;
>>> struct rcu_head rcu;
>>> +
>>> + /* split BTF support */
>>> + struct btf *base_btf;
>>> + u32 start_id; /* first type ID in this BTF (0 for base BTF) */
>>> + u32 start_str_off; /* first string offset (0 for base BTF) */
>>> };
>>>
>>> enum verifier_phase {
>>> @@ -449,14 +454,27 @@ static bool btf_type_is_datasec(const struct btf_type *t)
>>> return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
>>> }
>>>
>>> +static u32 btf_nr_types_total(const struct btf *btf)
>>> +{
>>> + u32 total = 0;
>>> +
>>> + while (btf) {
>>> + total += btf->nr_types;
>>> + btf = btf->base_btf;
>>> + }
>>> +
>>> + return total;
>>> +}
>>> +
>>> s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind)
>>> {
>>> const struct btf_type *t;
>>> const char *tname;
>>> - u32 i;
>>> + u32 i, total;
>>>
>>> - for (i = 1; i <= btf->nr_types; i++) {
>>> - t = btf->types[i];
>>> + total = btf_nr_types_total(btf);
>>> + for (i = 1; i < total; i++) {
>>> + t = btf_type_by_id(btf, i);
>>> if (BTF_INFO_KIND(t->info) != kind)
>>> continue;
>>>
>>> @@ -599,8 +617,14 @@ static const struct btf_kind_operations *btf_type_ops(const struct btf_type *t)
>>>
>>> static bool btf_name_offset_valid(const struct btf *btf, u32 offset)
>>> {
>>> - return BTF_STR_OFFSET_VALID(offset) &&
>>> - offset < btf->hdr.str_len;
>>> + if (!BTF_STR_OFFSET_VALID(offset))
>>> + return false;
>>> +
>>> + while (offset < btf->start_str_off)
>>> + btf = btf->base_btf;
>>
>> Do we need "if (!btf) return false;" in the while loop? (and some other loops below)
>
> No, because for base btf start_str_off and start_type_id are always
> zero, so loop condition is always false.
Ah, I misread the code. Thanks for the explanation.
Acked-by: Song Liu <songliubraving@xxxxxx>
