> 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)
[...]
