> On Nov 6, 2020, at 3:02 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>
[...]
>
> @@ -600,8 +618,15 @@ 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;
> +again:
> + if (offset < btf->start_str_off) {
> + btf = btf->base_btf;
> + goto again;
Can we do a while loop instead of "goto again;"?
> + }
> + offset -= btf->start_str_off;
> + return offset < btf->hdr.str_len;
> }
>
> static bool __btf_name_char_ok(char c, bool first, bool dot_ok)
> @@ -615,10 +640,25 @@ static bool __btf_name_char_ok(char c, bool first, bool dot_ok)
> return true;
> }
>
> +static const char *btf_str_by_offset(const struct btf *btf, u32 offset)
> +{
> +again:
> + if (offset < btf->start_str_off) {
> + btf = btf->base_btf;
> + goto again;
> + }
Maybe add a btf_find_base_btf(btf, offset) helper for this logic?
> +
> + offset -= btf->start_str_off;
> + if (offset < btf->hdr.str_len)
> + return &btf->strings[offset];
> +
> + return NULL;
> +}
> +
[...]
> }
>
> const char *btf_name_by_offset(const struct btf *btf, u32 offset)
> {
> - if (offset < btf->hdr.str_len)
> - return &btf->strings[offset];
> -
> - return NULL;
> + return btf_str_by_offset(btf, offset);
> }
IIUC, btf_str_by_offset() and btf_name_by_offset() are identical. Can we
just keep btf_name_by_offset()?
>
> const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id)
> {
> - if (type_id > btf->nr_types)
> - return NULL;
> +again:
> + if (type_id < btf->start_id) {
> + btf = btf->base_btf;
> + goto again;
> + }
ditto, goto again..
[...]
