On Mon, Jun 22, 2026 at 7:37 AM Leon Hwang <[email protected]> wrote:
>
> Enhance bpftool to generate skeletons that properly handle global percpu
> variables. The generated skeleton now includes a dedicated structure for
> percpu data, allowing users to initialize and access percpu variables more
> efficiently.
>
> For global percpu variables, the skeleton now includes a nested
> structure, e.g.:
>
> struct test_global_percpu_data {
> struct bpf_object_skeleton *skeleton;
> struct bpf_object *obj;
> struct {
> struct bpf_map *percpu;
> } maps;
> // ...
> struct test_global_percpu_data__percpu {
> int data;
> char run;
> struct {
> char set;
> int i;
> int nums[7];
> } struct_data;
> int nums[7];
> } *percpu;
>
> // ...
> };
>
> * The "struct test_global_percpu_data__percpu *percpu" points to
> initialized data, which is actually "maps.percpu->mmaped".
> * Before loading the skeleton, updating the
> "struct test_global_percpu_data__percpu *percpu" modifies the initial
> value of the corresponding global percpu variables.
> * After loading the skeleton, "maps.percpu->mmaped" has been marked as
> read-only in libbpf. If users want to update the global percpu
> variables, they have to update the "maps.percpu" map instead.
> * For lightweight skeleton, "lskel->percpu" will be protected by
> "mprotect(p, sz, PROT_READ)".
> * For subskeleton, those variables of global percpu data will be
> skipped.
>
> Assisted-by: Codex:gpt-5.5-xhigh
> Signed-off-by: Leon Hwang <[email protected]>
> ---
> tools/bpf/bpftool/gen.c | 43 +++++++++++++++++++++++++++--------
> tools/lib/bpf/skel_internal.h | 24 +++++++++++++++++--
> 2 files changed, 56 insertions(+), 11 deletions(-)
>
[...]
> @@ -263,13 +268,12 @@ static bool is_mmapable_map(const struct bpf_map *map,
> char *buf, size_t sz)
> return true;
> }
>
> - if (!bpf_map__is_internal(map) || !(bpf_map__map_flags(map) &
> BPF_F_MMAPABLE))
> - return false;
> -
> - if (!get_map_ident(map, buf, sz))
> - return false;
> + if (bpf_map__is_internal(map) &&
> + ((bpf_map__map_flags(map) & BPF_F_MMAPABLE) ||
> bpf_map_is_percpu_data(map)) &&
> + get_map_ident(map, buf, sz))
> + return true;
>
just add `if (bpf_map_is_percpu_data(map) return true;`? maybe also
move get_map_ident check a bit earlier. I think that will be a bit
cleaner, this condition is quite hard to follow
> - return true;
> + return false;
> }
>
> static int codegen_datasecs(struct bpf_object *obj, const char *obj_name)
> @@ -343,6 +347,9 @@ static int codegen_subskel_datasecs(struct bpf_object
> *obj, const char *obj_name
> if (!is_mmapable_map(map, map_ident, sizeof(map_ident)))
> continue;
>
> + if (bpf_map_is_percpu_data(map))
> + continue;
> +
> sec = find_type_for_map(btf, map_ident);
> if (!sec)
> continue;
> @@ -669,7 +676,7 @@ static void codegen_destroy(struct bpf_object *obj, const
> char *obj_name)
> if (!get_map_ident(map, ident, sizeof(ident)))
> continue;
> if (bpf_map__is_internal(map) &&
> - (bpf_map__map_flags(map) & BPF_F_MMAPABLE))
> + ((bpf_map__map_flags(map) & BPF_F_MMAPABLE) ||
> bpf_map_is_percpu_data(map)))
also we can add a helper to check if it's an internal map with a
dedicated data section in the skeleton (too lazy to think of a good
name right now.. ;)
> printf("\tskel_free_map_data(skel->%1$s,
> skel->maps.%1$s.initial_value, %2$zu);\n",
> ident, bpf_map_mmap_sz(map));
> codegen("\
[...]
