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libbpf: Support sanitization of BTF layout for older kernels

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Add a FEAT_BTF_LAYOUT feature check which checks if the
kernel supports BTF layout information.  Also sanitize
BTF if it contains layout data but the kernel does not
support it.  The sanitization requires rewriting raw
BTF data to update the header and eliminate the layout
section (since it lies between the types and strings),
so refactor sanitization to do the raw BTF retrieval
and creation of updated BTF, returning that new BTF
on success.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260326145444.2076244-7-alan.maguire@oracle.com
This commit is contained in:
Alan Maguire authored and Andrii Nakryiko committed 2026-04-09 15:12:21 -07:00
1 parent c95ad95d0a
commit fd04b4eae1
4 files changed
+131 -40
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src/libbpf_probes.c
+29 -19
View File
@@ -218,6 +218,34 @@ int libbpf_probe_bpf_prog_type(enum bpf_prog_type prog_type, const void *opts)
return libbpf_err(ret);
}
int libbpf__load_raw_btf_hdr(const struct btf_header *hdr, const char *raw_types,
const char *str_sec, const char *layout_sec,
int token_fd)
{
LIBBPF_OPTS(bpf_btf_load_opts, opts,
.token_fd = token_fd,
.btf_flags = token_fd ? BPF_F_TOKEN_FD : 0,
);
int btf_fd, btf_len;
__u8 *raw_btf;
btf_len = hdr->hdr_len + hdr->type_off + hdr->type_len + hdr->str_len + hdr->layout_len;
raw_btf = malloc(btf_len);
if (!raw_btf)
return -ENOMEM;
memcpy(raw_btf, hdr, sizeof(*hdr));
memcpy(raw_btf + hdr->hdr_len + hdr->type_off, raw_types, hdr->type_len);
memcpy(raw_btf + hdr->hdr_len + hdr->str_off, str_sec, hdr->str_len);
if (layout_sec)
memcpy(raw_btf + hdr->hdr_len + hdr->layout_off, layout_sec, hdr->layout_len);
btf_fd = bpf_btf_load(raw_btf, btf_len, &opts);
free(raw_btf);
return btf_fd;
}
int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
const char *str_sec, size_t str_len,
int token_fd)
@@ -230,26 +258,8 @@ int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
.str_off = types_len,
.str_len = str_len,
};
LIBBPF_OPTS(bpf_btf_load_opts, opts,
.token_fd = token_fd,
.btf_flags = token_fd ? BPF_F_TOKEN_FD : 0,
);
int btf_fd, btf_len;
__u8 *raw_btf;
btf_len = hdr.hdr_len + hdr.type_len + hdr.str_len;
raw_btf = malloc(btf_len);
if (!raw_btf)
return -ENOMEM;
memcpy(raw_btf, &hdr, sizeof(hdr));
memcpy(raw_btf + hdr.hdr_len, raw_types, hdr.type_len);
memcpy(raw_btf + hdr.hdr_len + hdr.type_len, str_sec, hdr.str_len);
btf_fd = bpf_btf_load(raw_btf, btf_len, &opts);
free(raw_btf);
return btf_fd;
return libbpf__load_raw_btf_hdr(&hdr, raw_types, str_sec, NULL, token_fd);
}
static int load_local_storage_btf(void)