On Wed, Feb 5, 2025 at 11:09 AM Blaise Boscaccy
<bboscaccy@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Add a flexible mechanism, using existing ELF constructs, to attach
> additional metadata to BPF programs for possible use by BPF
> gatekeepers and skeletons.
>
> During object file parsing, note sections are no longer skipped and
> now treated as read-only data. During libbpf-based loading or skeleton
> generation, those sections are then transformed into read-only maps
> which are subsequently passed into the kernel.
We already have this mechanism, it's .rodata (and
.rodata.<customname>) section(s). Adding .note sections as BPF maps
make no sense to me. Just piggy-back on .rodata for storing any
necessary metadata.
pw-bot: cr
>
> Signed-off-by: Blaise Boscaccy <bboscaccy@xxxxxxxxxxxxxxxxxxx>
> ---
> tools/bpf/bpftool/gen.c | 4 ++--
> tools/lib/bpf/libbpf.c | 6 ++++++
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 5a4d3240689ed..311d6a3f1c4bb 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -92,7 +92,7 @@ static void get_header_guard(char *guard, const char *obj_name, const char *suff
>
> static bool get_map_ident(const struct bpf_map *map, char *buf, size_t buf_sz)
> {
> - static const char *sfxs[] = { ".data", ".rodata", ".bss", ".kconfig" };
> + static const char *sfxs[] = { ".data", ".rodata", ".bss", ".kconfig", ".note" };
> const char *name = bpf_map__name(map);
> int i, n;
>
> @@ -117,7 +117,7 @@ static bool get_map_ident(const struct bpf_map *map, char *buf, size_t buf_sz)
>
> static bool get_datasec_ident(const char *sec_name, char *buf, size_t buf_sz)
> {
> - static const char *pfxs[] = { ".data", ".rodata", ".bss", ".kconfig" };
> + static const char *pfxs[] = { ".data", ".rodata", ".bss", ".kconfig", ".note" };
> int i, n;
>
> /* recognize hard coded LLVM section name */
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 194809da51725..be6af0fece040 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -523,6 +523,7 @@ struct bpf_struct_ops {
> #define STRUCT_OPS_SEC ".struct_ops"
> #define STRUCT_OPS_LINK_SEC ".struct_ops.link"
> #define ARENA_SEC ".addr_space.1"
> +#define NOTE_SEC ".note"
>
> enum libbpf_map_type {
> LIBBPF_MAP_UNSPEC,
> @@ -3977,6 +3978,11 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> sec_desc->sec_type = SEC_BSS;
> sec_desc->shdr = sh;
> sec_desc->data = data;
> + } else if (sh->sh_type == SHT_NOTE && (strcmp(name, NOTE_SEC) == 0 ||
> + str_has_pfx(name, NOTE_SEC "."))) {
> + sec_desc->sec_type = SEC_RODATA;
> + sec_desc->shdr = sh;
> + sec_desc->data = data;
> } else {
> pr_info("elf: skipping section(%d) %s (size %zu)\n", idx, name,
> (size_t)sh->sh_size);
> --
> 2.48.1
>
