2023-11-12 12:49 UTC+0000 ~ Alan Maguire <alan.maguire@xxxxxxxxxx>
> Provide a way to dump BTF metadata info via bpftool; this
> consists of BTF size, header fields and kind layout info
> (if available); for example
>
> $ bpftool btf dump file vmlinux format meta
> size 5161076
> magic 0xeb9f
> version 1
> flags 0x1
> hdr_len 40
> type_len 3036368
> type_off 0
> str_len 2124588
> str_off 3036368
> kind_layout_len 80
> kind_layout_off 5160956
> crc 0x64af901b
> base_crc 0x0
> kind 0 UNKNOWN flags 0x0 info_sz 0 elem_sz 0
> kind 1 INT flags 0x0 info_sz 0 elem_sz 0
> kind 2 PTR flags 0x0 info_sz 0 elem_sz 0
> kind 3 ARRAY flags 0x0 info_sz 0 elem_sz 0
> kind 4 STRUCT flags 0x35 info_sz 0 elem_sz 0
> ...
>
> JSON output is also supported:
>
> $ bpftool -j btf dump file vmlinux format meta
> {"size":5161076,"header":{"magic":60319,"version":1,"flags":1,"hdr_len":40,"type_len":3036368,"type_off":0,"str_len":2124588,"str_off":3036368,"kind_layout_len":80,"kind_layout_offset":5160956,"crc":1689227291,"base_crc":0},"kind_layouts":[{"kind":0,"name":"UNKNOWN","flags":0,"info_sz":0,"elem_sz":0},{"kind":1,"name":"INT","flags":0,"info_sz":0,"elem_sz":0},{"kind":2,"name":"PTR","flags":0,"info_sz":0,"elem_sz":0},{"kind":3,"name":"ARRAY","flags":0,"info_sz":0,"elem_sz":0},{"kind":4,"name":"STRUCT","flags":53,"info_sz":0,"elem_sz":0},{"kind":5,"name":"UNION","flags":0,"info_sz":0,"elem_sz":0},{"kind":6,"name":"ENUM","flags":60319,"info_sz":1,"elem_sz":1},{"kind":7,"name":"FWD","flags":40,"info_sz":0,"elem_sz":0},{"kind":8,"name":"TYPEDEF","flags":0,"info_sz":0,"elem_sz":0},{"kind":9,"name":"VOLATILE","flags":0,"info_sz":0,"elem_sz":0},{"kind":10,"name":"CONST","flags":0,"info_sz":0,"elem_sz":0},{"kind":11,"name":"RESTRICT","flags":1,"info_sz":0,"elem_sz":0},{"kind":12,"name":"FUNC","flags":0,"info_sz":0,"elem_sz":0},{"kind":13,"name":"FUNC_PROTO","flags":80,"info_sz":0,"elem_sz":0},{"kind":14,"name":"VAR","flags":0,"info_sz":0,"elem_sz":0},{"kind":15,"name":"DATASEC","flags":0,"info_sz":0,"elem_sz":0},{"kind":16,"name":"FLOAT","flags":53,"info_sz":0,"elem_sz":0},{"kind":17,"name":"DECL_TAG","flags":0,"info_sz":0,"elem_sz":0},{"kind":18,"name":"TYPE_TAG","flags":11441,"info_sz":3,"elem_sz":0},{"kind":19,"name":"ENUM64","flags":0,"info_sz":0,"elem_sz":0}]}
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> tools/bpf/bpftool/bash-completion/bpftool | 2 +-
> tools/bpf/bpftool/btf.c | 91 ++++++++++++++++++++++-
> 2 files changed, 90 insertions(+), 3 deletions(-)
>
> diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
> index 6e4f7ce6bc01..157c3afd8247 100644
> --- a/tools/bpf/bpftool/bash-completion/bpftool
> +++ b/tools/bpf/bpftool/bash-completion/bpftool
> @@ -937,7 +937,7 @@ _bpftool()
> return 0
> ;;
> format)
> - COMPREPLY=( $( compgen -W "c raw" -- "$cur" ) )
> + COMPREPLY=( $( compgen -W "c raw meta" -- "$cur" ) )
> ;;
> *)
> # emit extra options
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 91fcb75babe3..208f3a587534 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -504,6 +504,88 @@ static int dump_btf_c(const struct btf *btf,
> return err;
> }
>
> +static int dump_btf_meta(const struct btf *btf)
> +{
> + const struct btf_header *hdr;
> + const struct btf_kind_layout *k;
> + __u8 i, nr_kinds = 0;
> + const void *data;
> + __u32 data_sz;
> +
> + data = btf__raw_data(btf, &data_sz);
> + if (!data)
> + return -ENOMEM;
> + hdr = data;
> + if (json_output) {
> + jsonw_start_object(json_wtr); /* btf metadata object */
Nit: Please make sure to be consistent when aligning these comments:
there are several occurrences with spaces (here three spaces), several
ones with tabs. For these, I'd prefer tabs to align the start and end
comments for a given object/array, although I don't really using a
single space as well as long as we keep it consistent.
> + jsonw_uint_field(json_wtr, "size", data_sz);
> + jsonw_name(json_wtr, "header");
> + jsonw_start_object(json_wtr); /* btf header object */
> + jsonw_uint_field(json_wtr, "magic", hdr->magic);
> + jsonw_uint_field(json_wtr, "version", hdr->version);
> + jsonw_uint_field(json_wtr, "flags", hdr->flags);
> + jsonw_uint_field(json_wtr, "hdr_len", hdr->hdr_len);
> + jsonw_uint_field(json_wtr, "type_len", hdr->type_len);
> + jsonw_uint_field(json_wtr, "type_off", hdr->type_off);
> + jsonw_uint_field(json_wtr, "str_len", hdr->str_len);
> + jsonw_uint_field(json_wtr, "str_off", hdr->str_off);
> + } else {
> + printf("size %-10d\n", data_sz);
> + printf("magic 0x%-10x\nversion %-10d\nflags 0x%-10x\nhdr_len %-10d\n",
> + hdr->magic, hdr->version, hdr->flags, hdr->hdr_len);
> + printf("type_len %-10d\ntype_off %-10d\n", hdr->type_len, hdr->type_off);
> + printf("str_len %-10d\nstr_off %-10d\n", hdr->str_len, hdr->str_off);
> + }
> +
> + if (hdr->hdr_len < sizeof(struct btf_header)) {
> + if (json_output) {
> + jsonw_end_object(json_wtr); /* header object */
> + jsonw_end_object(json_wtr); /* metadata object */
Similarly, can you please keep consistent comment strings? "metadata
object" here vs. "end metadata" below.
> + }
> + return 0;
> + }
> + if (hdr->kind_layout_len > 0 && hdr->kind_layout_off > 0) {
> + k = (void *)hdr + hdr->hdr_len + hdr->kind_layout_off;
> + nr_kinds = hdr->kind_layout_len / sizeof(*k);
> + }
> + if (json_output) {
> + jsonw_uint_field(json_wtr, "kind_layout_len", hdr->kind_layout_len);
> + jsonw_uint_field(json_wtr, "kind_layout_offset", hdr->kind_layout_off);
> + jsonw_uint_field(json_wtr, "crc", hdr->crc);
> + jsonw_uint_field(json_wtr, "base_crc", hdr->base_crc);
> + jsonw_end_object(json_wtr); /* end header object */
> +
> + if (nr_kinds > 0) {
> + jsonw_name(json_wtr, "kind_layouts");
> + jsonw_start_array(json_wtr);
> + for (i = 0; i < nr_kinds; i++) {
> + jsonw_start_object(json_wtr);
> + jsonw_uint_field(json_wtr, "kind", i);
> + if (i < NR_BTF_KINDS)
> + jsonw_string_field(json_wtr, "name", btf_kind_str[i]);
I prefer to avoid conditional fields in JSON, especially in an array
it's easier to process the JSON if all items have the same structure.
Would it make sense to keep the "name" field, but use jsonw_null() (or
"UNKNOWN") for the value when there's no name to print?
Thanks,
Quentin
