[PATCH bpf-next 03/16] libbpf: Place the percpu chunks in the bpf arena

[Xu Kuohai]

From: Xu Kuohai <xukuohai@xxxxxxxxxx>

Place the percpu chunks in the bpf arena, alongside the global arena
data.

When full-range ldimm64 offset is supported, the global data sits at
the end of the arena, place the percpu chunks right before it:

+------------+---------+---------+----+---------+--------+
|            | percpu  | percpu  |... | percpu  | global |
|            | chunk 0 | chunk 1 |    | chunk N | data   |
+------------+---------+---------+----+---------+--------+

Otherwise, the global data region sits at the beginning, place the
percpu chunks right after it:

+---------+---------+---------+----+---------+------------+
| global  | percpu  | percpu  |... | percpu  |            |
| data    | chunk 0 | chunk 1 |    | chunk N |            |
+---------+---------+---------+----+---------+------------+

Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
 tools/lib/bpf/libbpf.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 02ee57e3f6c7..6fc8c7f549d9 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -833,6 +833,7 @@ struct bpf_object {
 		void *chunk; /* copy from section .arena.percpu, zero-padded to chunk size */
 		size_t chunk_sz;	/* chunk size, page-aligned */
 		size_t nr_chunks;	/* how many chunks, one chunk per possible cpu */
+		size_t offset;		/* offset within the arena */
 		bool present;
 	} arena_percpu;
 
@@ -8212,8 +8213,12 @@ static int bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_pat
 		}
 
 		/* place globals at the end of the arena (if supported) */
-		if (kernel_supports(obj, FEAT_LDIMM64_FULL_RANGE_OFF))
-			obj->arena_data_off = mmap_sz - data_sz;
+		if (kernel_supports(obj, FEAT_LDIMM64_FULL_RANGE_OFF)) {
+			obj->arena_data_off = data_sz ? mmap_sz - data_sz : 0;
+			obj->arena_percpu.offset = mmap_sz - data_sz - percpu_sz;
+		} else {
+			obj->arena_percpu.offset = data_sz;
+		}
 	}
 
 	err = bpf_object__relocate_data_ptrs(obj);
-- 
2.47.3