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[v2,bpf-next,3/6] libbpf: support static map definitions

Message ID 20210423185357.1992756-4-andrii@kernel.org (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series BPF static linker: support static vars and maps | expand

Checks

Context Check Description
netdev/apply fail Patch does not apply to bpf-next
netdev/tree_selection success Clearly marked for bpf-next

Commit Message

Andrii Nakryiko April 23, 2021, 6:53 p.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(-)

Comments

Yonghong Song April 23, 2021, 8:25 p.m. UTC | #1 
On 4/23/21 11:53 AM, Andrii Nakryiko wrote:
> 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>

Acked-by: Yonghong Song <yhs@fb.com>
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a1cddd17af7d..6c755c5f037d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3633,6 +3633,8 @@  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);
@@ -3642,7 +3644,7 @@  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,
@@ -3657,7 +3659,8 @@  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;
 	}