[PATCH bpf-next 01/16] libbpf: Collect arena percpu data section

[Xu Kuohai]

From: Xu Kuohai <xukuohai@xxxxxxxxxx>

Introduce a new section ".arena.percpu" for the bpf arena. A variable
in this section lives in the bpf arena and has a separate value for
each possible CPU. The initial value is replicated for each CPU at
load time.

Collect the section's data and index so the later steps can size,
place and relocate it.

Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
 tools/lib/bpf/libbpf.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8fcb8cf39cc0..d79fc382319e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -573,6 +573,13 @@ struct bpf_struct_ops {
  */
 #define ARENA_DATA_SEC ".arena.data"
 
+/*
+ * A variable in this section is arena percpu data. It lives in the bpf
+ * arena and has a separate value for each possible CPU. The initial value
+ * is replicated for each CPU at load time.
+ */
+#define ARENA_PERCPU_SEC ".arena.percpu"
+
 enum libbpf_map_type {
 	LIBBPF_MAP_UNSPEC,
 	LIBBPF_MAP_DATA,
@@ -718,6 +725,7 @@ struct elf_state {
 	Elf64_Ehdr *ehdr;
 	Elf_Data *symbols;
 	Elf_Data *arena_data;
+	Elf_Data *arena_percpu_data;
 	size_t shstrndx; /* section index for section name strings */
 	size_t strtabidx;
 	struct elf_sec_desc *secs;
@@ -728,6 +736,7 @@ struct elf_state {
 	int symbols_shndx;
 	bool has_st_ops;
 	int arena_data_shndx;
+	int arena_percpu_shndx;
 	int jumptables_data_shndx;
 };
 
@@ -1645,6 +1654,7 @@ static struct bpf_object *bpf_object__new(const char *path,
 	obj->efile.obj_buf_sz = obj_buf_sz;
 	obj->efile.btf_maps_shndx = -1;
 	obj->efile.arena_data_shndx = -1;
+	obj->efile.arena_percpu_shndx = -1;
 	obj->kconfig_map_idx = -1;
 	obj->arena_map_idx = -1;
 
@@ -1664,6 +1674,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
 	obj->efile.ehdr = NULL;
 	obj->efile.symbols = NULL;
 	obj->efile.arena_data = NULL;
+	obj->efile.arena_percpu_data = NULL;
 
 	zfree(&obj->efile.secs);
 	obj->efile.sec_cnt = 0;
@@ -3201,7 +3212,7 @@ static int bpf_object__init_arena_data(struct bpf_object *obj)
 
 	if (obj->arena_map_idx < 0) {
 		/* bpf_object__init_user_btf_maps() didn't look: there is no .maps section */
-		if (obj->efile.arena_data) {
+		if (obj->efile.arena_data || obj->efile.arena_percpu_data) {
 			pr_warn("elf: sec '%s': to use global __arena variables the ARENA map should be explicitly declared in SEC(\".maps\")\n",
 				ARENA_SEC);
 			return -ENOENT;
@@ -3331,6 +3342,12 @@ static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
 		return -ENOENT;
 	}
 
+	if (obj->efile.arena_percpu_data && obj->arena_map_idx < 0) {
+		pr_warn("elf: sec '%s': to use arena percpu variables the ARENA map should be explicitly declared in SEC(\".maps\")\n",
+			ARENA_PERCPU_SEC);
+		return -ENOENT;
+	}
+
 	return 0;
 }
 
@@ -4286,6 +4303,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 				obj->efile.arena_data_shndx = idx;
 			} else if (strcmp(name, ARENA_DATA_SEC) == 0) {
 				/* the marker, see the first pass */
+			} else if (strcmp(name, ARENA_PERCPU_SEC) == 0) {
+				obj->efile.arena_percpu_data = data;
+				obj->efile.arena_percpu_shndx = idx;
 			} else if (strcmp(name, JUMPTABLES_SEC) == 0) {
 				obj->jumptables_data = malloc(data->d_size);
 				if (!obj->jumptables_data)
-- 
2.47.3