2023-05-31 21:19 UTC+0100 ~ Alan Maguire <alan.maguire@xxxxxxxxxx>
> Provide a way to dump BTF header and metadata info via
> bpftool; for example
>
> $ bpftool btf dump file vmliux format meta
Typo: vmliux
> BTF: data size 4963656
> Header: magic 0xeb9f, version 1, flags 0x0, hdr_len 32
> Types: len 2927556, offset 0
> Strings: len 2035881, offset 2927556
> Metadata header found: len 184, offset 4963440, flags 0x1
> Description: 'generated by dwarves v1.25'
> CRC 0x6da2a930 ; base CRC 0x0
> Kind metadata for 20 kinds:
> BTF_KIND_UNKN[ 0] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_INT[ 1] flags 0x0 info_sz 4 elem_sz 0
> BTF_KIND_PTR[ 2] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_ARRAY[ 3] flags 0x0 info_sz 12 elem_sz 0
> BTF_KIND_STRUCT[ 4] flags 0x0 info_sz 0 elem_sz 12
> BTF_KIND_UNION[ 5] flags 0x0 info_sz 0 elem_sz 12
> BTF_KIND_ENUM[ 6] flags 0x0 info_sz 0 elem_sz 8
> BTF_KIND_FWD[ 7] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_TYPEDEF[ 8] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_VOLATILE[ 9] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_CONST[10] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_RESTRICT[11] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_FUNC[12] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_FUNC_PROTO[13] flags 0x0 info_sz 0 elem_sz 8
> BTF_KIND_VAR[14] flags 0x0 info_sz 4 elem_sz 0
> BTF_KIND_DATASEC[15] flags 0x0 info_sz 0 elem_sz 12
> BTF_KIND_FLOAT[16] flags 0x0 info_sz 0 elem_sz 0
> BTF_KIND_DECL_TAG[17] flags 0x1 info_sz 4 elem_sz 0
> BTF_KIND_TYPE_TAG[18] flags 0x1 info_sz 0 elem_sz 0
> BTF_KIND_ENUM64[19] flags 0x0 info_sz 0 elem_sz 12
>
Thanks for this! For the non-RFC, can you please add the following:
- JSON output
- btf.c's do_help() update
- Documentation/bpftool-btf.rst update (cmd summary, and description)
- bash-completion/bpftool update (should be straightforward, we just
need to offer "metadata" after "format", like we already offer "c" and
"raw".
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> tools/bpf/bpftool/btf.c | 46 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 46 insertions(+)
>
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 91fcb75babe3..da4257e00ba8 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -504,6 +504,47 @@ 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_metadata *m;
> + const void *data;
> + __u32 data_sz;
> + __u8 i;
> +
> + data = btf__raw_data(btf, &data_sz);
> + if (!data)
> + return -ENOMEM;
> + hdr = data;
> + printf("BTF: data size %u\n", data_sz);
> + printf("Header: magic 0x%x, version %d, flags 0x%x, hdr_len %u\n",
> + hdr->magic, hdr->version, hdr->flags, hdr->hdr_len);
Nit: bpftool's output fields don't usually start with a capital letter
(save for acronyms, obviously). I don't mind much, though.
> + printf("Types: len %u, offset %u\n", hdr->type_len, hdr->type_off);
> + printf("Strings: len %u, offset %u\n", hdr->str_len, hdr->str_off);
> +
> + if (hdr->hdr_len < sizeof(struct btf_header) ||
> + hdr->meta_header.meta_len == 0 ||
> + hdr->meta_header.meta_off == 0)
> + return 0;
> +
> + m = (void *)hdr + hdr->hdr_len + hdr->meta_header.meta_off;
> +
> + printf("Metadata header found: len %u, offset %u, flags 0x%x\n",
> + hdr->meta_header.meta_len, hdr->meta_header.meta_off, m->flags);
> + if (m->description_off)
> + printf("Description: '%s'\n", btf__name_by_offset(btf, m->description_off));
> + printf("CRC 0x%x ; base CRC 0x%x\n", m->crc, m->base_crc);
> + printf("Kind metadata for %d kinds:\n", m->kind_meta_cnt);
> + for (i = 0; i < m->kind_meta_cnt; i++) {
> + printf("%20s[%2d] flags 0x%-4x info_sz %2d elem_sz %2d\n",
> + btf__name_by_offset(btf, m->kind_meta[i].name_off),
> + i, m->kind_meta[i].flags, m->kind_meta[i].info_sz,
> + m->kind_meta[i].elem_sz);
Nit: I would maybe add a double space for separating the different
field, especially because we have some left padding for values < 10 in
your example and it looks strange to have numbers closer to the next
field name (on their right) rather than their own (on their left).
> + }
> +
> + return 0;
> +}
> +
> static const char sysfs_vmlinux[] = "/sys/kernel/btf/vmlinux";
>
> static struct btf *get_vmlinux_btf_from_sysfs(void)
> @@ -553,6 +594,7 @@ static int do_dump(int argc, char **argv)
> __u32 root_type_ids[2];
> int root_type_cnt = 0;
> bool dump_c = false;
> + bool dump_meta = false;
> __u32 btf_id = -1;
> const char *src;
> int fd = -1;
> @@ -654,6 +696,8 @@ static int do_dump(int argc, char **argv)
> }
> if (strcmp(*argv, "c") == 0) {
> dump_c = true;
> + } else if (strcmp(*argv, "meta") == 0) {
> + dump_meta = true;
We could use is_prefix() instead of strcmp() (same for "raw" below, by
the way), to make it possible to pass the keyword by prefix (as in
"bpftool b d f vmlinux f m".
> } else if (strcmp(*argv, "raw") == 0) {
> dump_c = false;
> } else {
> @@ -692,6 +736,8 @@ static int do_dump(int argc, char **argv)
> goto done;
> }
> err = dump_btf_c(btf, root_type_ids, root_type_cnt);
> + } else if (dump_meta) {
> + err = dump_btf_meta(btf);
> } else {
> err = dump_btf_raw(btf, root_type_ids, root_type_cnt);
> }
