On Tue, May 28, 2024 at 5:25 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>
> Share relocation implementation with the kernel. As part of this,
> we also need the type/string visitation functions so add them to a
> btf_common.c file that also gets shared with the kernel. Relocation
> code in kernel and userspace is identical save for the impementation
> of the reparenting of split BTF to the relocated base BTF and
> retrieval of BTF header from "struct btf"; these small functions
> need separate user-space and kernel implementations.
>
> One other wrinkle on the kernel side is we have to map .BTF.ids in
> modules as they were generated with the type ids used at BTF encoding
> time. btf_relocate() optionally returns an array mapping from old BTF
> ids to relocated ids, so we use that to fix up these references where
> needed for kfuncs.
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> include/linux/btf.h | 45 ++++++++++
> kernel/bpf/Makefile | 10 ++-
> kernel/bpf/btf.c | 168 +++++++++++++++++++++++++----------
> tools/lib/bpf/Build | 2 +-
> tools/lib/bpf/btf.c | 130 ---------------------------
> tools/lib/bpf/btf_iter.c | 143 +++++++++++++++++++++++++++++
> tools/lib/bpf/btf_relocate.c | 23 +++++
> 7 files changed, 344 insertions(+), 177 deletions(-)
> create mode 100644 tools/lib/bpf/btf_iter.c
>
[...]
> +static inline struct btf_decl_tag *btf_decl_tag(const struct btf_type *t)
> +{
> + return (struct btf_decl_tag *)(t + 1);
> +}
> +
> static inline int btf_id_cmp_func(const void *a, const void *b)
> {
> const int *pa = a, *pb = b;
> @@ -515,9 +528,17 @@ static inline const struct bpf_struct_ops_desc *bpf_struct_ops_find(struct btf *
> }
> #endif
>
> +typedef int (*type_id_visit_fn)(__u32 *type_id, void *ctx);
> +typedef int (*str_off_visit_fn)(__u32 *str_off, void *ctx);
> +
let me take a quick stab at implementing type/str field iterator in
libbpf. If I don't get stuck anywhere, maybe you can just rebase on
that and avoid the callback hell and the need for this
callback-vs-iter churn in the kernel code as well
> #ifdef CONFIG_BPF_SYSCALL
> const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);
> +void btf_set_base_btf(struct btf *btf, const struct btf *base_btf);
> +int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **map_ids);
> +int btf_type_visit_type_ids(struct btf_type *t, type_id_visit_fn visit, void *ctx);
> +int btf_type_visit_str_offs(struct btf_type *t, str_off_visit_fn visit, void *ctx);
> const char *btf_name_by_offset(const struct btf *btf, u32 offset);
> +const char *btf_str_by_offset(const struct btf *btf, u32 offset);
> struct btf *btf_parse_vmlinux(void);
> struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog);
> u32 *btf_kfunc_id_set_contains(const struct btf *btf, u32 kfunc_btf_id,
[...]
