Re: [PATCH bpf-next v8 5/9] bpftool: Generate skeleton for global percpu data

[Quentin Monnet <qmo@kernel.org>]

2026-06-29 23:24 UTC+0800 ~ Leon Hwang <leon.hwang@linux.dev>
> 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 <leon.hwang@linux.dev>
> ---
>  tools/bpf/bpftool/gen.c       | 49 +++++++++++++++++++++++++++++++----
>  tools/lib/bpf/skel_internal.h | 24 +++++++++++++++--
>  2 files changed, 66 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 6ae7262ebe0c..2e60296358db 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", ".percpu", ".kconfig" };
>  	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", ".percpu", ".kconfig" };
>  	int i, n;
>  
>  	/* recognize hard coded LLVM section name */
> @@ -254,6 +254,20 @@ static const struct btf_type *find_type_for_map(struct btf *btf, const char *map
>  	return NULL;
>  }
>  
> +static bool bpf_map_is_skel_data(const struct bpf_map *map)
> +{
> +	if (!bpf_map__is_internal(map))
> +		return false;
> +
> +	if (bpf_map__map_flags(map) & BPF_F_MMAPABLE)
> +		return true;
> +
> +	if (bpf_map__type(map) == BPF_MAP_TYPE_PERCPU_ARRAY)
> +		return true;
> +
> +	return false;
> +}
> +
>  static bool is_mmapable_map(const struct bpf_map *map, char *buf, size_t sz)
>  {
>  	size_t tmp_sz;
> @@ -263,7 +277,7 @@ 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))
> +	if (!bpf_map_is_skel_data(map))
>  		return false;
>  
>  	if (!get_map_ident(map, buf, sz))


Thanks! The bpftool patch looks good, with one reservation: after this
patch, I believe "is_mmapable_map(map, ...)" will return true if map is
a percpu map, although percpu maps aren't mmap-able, so we should
probably update the name of that function to avoid any confusion?

Quentin