[PATCH bpf-next 3/4] bpf, bpftool: Generate skeleton for global percpu data

[Leon Hwang <leon.hwang@linux.dev>]

This patch enhances bpftool to generate skeletons for global percpu
variables. The generated skeleton includes a dedicated structure for
percpu data, allowing users to initialize and access percpu variables
efficiently.

Changes:

1. skeleton structure:

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 *bss;
		struct bpf_map *percpu;
	} maps;
	// ...
	struct test_global_percpu_data__percpu {
		int percpu_data;
	} *percpu;

	// ...
};

  * The "struct test_global_percpu_data__percpu" points to initialized
    data, which is actually "maps.percpu->data".
  * Before loading the skeleton, updating the
    "struct test_global_percpu_data__percpu" modifies the initial value
    of the corresponding global percpu variables.
  * After loading the skeleton, accessing or updating this struct is no
    longer meaningful. Instead, users must interact with the global
    percpu variables via the "maps.percpu" map.

2. code changes:

  * Added support for ".percpu" sections in bpftool's map identification
    logic.
  * Modified skeleton generation to handle percpu data maps
    appropriately.
  * Updated libbpf to make "percpu" pointing to "maps.percpu->data".

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 tools/bpf/bpftool/gen.c | 13 +++++++++----
 tools/lib/bpf/libbpf.c  |  3 +++
 tools/lib/bpf/libbpf.h  |  1 +
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 5a4d3240689ed..975775683ca12 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", ".percpu", ".bss", ".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", ".percpu", ".bss", ".kconfig" };
 	int i, n;
 
 	/* recognize hard coded LLVM section name */
@@ -263,7 +263,9 @@ 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_internal(map) ||
+	    (!(bpf_map__map_flags(map) & BPF_F_MMAPABLE) &&
+	     bpf_map__type(map) != BPF_MAP_TYPE_PERCPU_ARRAY))
 		return false;
 
 	if (!get_map_ident(map, buf, sz))
@@ -903,7 +905,10 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped, bool
 			i, bpf_map__name(map), ident);
 		/* memory-mapped internal maps */
 		if (mmaped && is_mmapable_map(map, ident, sizeof(ident))) {
-			printf("\tmap->mmaped = (void **)&obj->%s;\n", ident);
+			if (bpf_map__type(map) == BPF_MAP_TYPE_PERCPU_ARRAY)
+				printf("\tmap->data = (void **)&obj->%s;\n", ident);
+			else
+				printf("\tmap->mmaped = (void **)&obj->%s;\n", ident);
 		}
 
 		if (populate_links && bpf_map__type(map) == BPF_MAP_TYPE_STRUCT_OPS) {
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6da6004c5c84d..dafb419bc5b86 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -13915,6 +13915,7 @@ static int populate_skeleton_maps(const struct bpf_object *obj,
 		struct bpf_map **map = map_skel->map;
 		const char *name = map_skel->name;
 		void **mmaped = map_skel->mmaped;
+		void **data = map_skel->data;
 
 		*map = bpf_object__find_map_by_name(obj, name);
 		if (!*map) {
@@ -13925,6 +13926,8 @@ static int populate_skeleton_maps(const struct bpf_object *obj,
 		/* externs shouldn't be pre-setup from user code */
 		if (mmaped && (*map)->libbpf_type != LIBBPF_MAP_KCONFIG)
 			*mmaped = (*map)->mmaped;
+		if (data && (*map)->libbpf_type == LIBBPF_MAP_PERCPU_DATA)
+			*data = (*map)->data;
 	}
 	return 0;
 }
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 3020ee45303a0..c49d6e44b5630 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1701,6 +1701,7 @@ struct bpf_map_skeleton {
 	const char *name;
 	struct bpf_map **map;
 	void **mmaped;
+	void **data;
 	struct bpf_link **link;
 };
 
-- 
2.47.1