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[bpf-next,3/6] libbpf: support static map definitions

Message ID 20210422014556.3451936-4-andrii@kernel.org
State Superseded
Headers show
Series BPF static linker: support static vars and maps | expand

Commit Message

Andrii Nakryiko April 22, 2021, 1:45 a.m. UTC 
Change libbpf relocation logic to support references to static map
definitions. This allows to use static maps and, combined with static linking,
hide internal maps from other files, just like static variables. User-space
will still be able to look up and modify static maps.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/libbpf.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
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Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 82b1946a0802..a7c3bcb8e5ea 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3632,6 +3632,8 @@  static int bpf_program__record_reloc(struct bpf_program *prog,
 
 	/* generic map reference relocation */
 	if (type == LIBBPF_MAP_UNSPEC) {
+		size_t map_offset = sym->st_value + insn->imm;
+
 		if (!bpf_object__shndx_is_maps(obj, shdr_idx)) {
 			pr_warn("prog '%s': bad map relo against '%s' in section '%s'\n",
 				prog->name, sym_name, sym_sec_name);
@@ -3641,7 +3643,7 @@  static int bpf_program__record_reloc(struct bpf_program *prog,
 			map = &obj->maps[map_idx];
 			if (map->libbpf_type != type ||
 			    map->sec_idx != sym->st_shndx ||
-			    map->sec_offset != sym->st_value)
+			    map->sec_offset != map_offset)
 				continue;
 			pr_debug("prog '%s': found map %zd (%s, sec %d, off %zu) for insn #%u\n",
 				 prog->name, map_idx, map->name, map->sec_idx,
@@ -3656,7 +3658,8 @@  static int bpf_program__record_reloc(struct bpf_program *prog,
 		reloc_desc->type = RELO_LD64;
 		reloc_desc->insn_idx = insn_idx;
 		reloc_desc->map_idx = map_idx;
-		reloc_desc->sym_off = 0; /* sym->st_value determines map_idx */
+		/* sym->st_value + insn->imm determines map_idx */
+		reloc_desc->sym_off = 0;
 		return 0;
 	}