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btf: Preserve string relocation maps for split BTF

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Make btf_relocate() optionally return the string-offset map it builds
while relocating a BTF relative to a distilled base. A subsequent split
BTF object can use that map to rebase references to base strings.

Also account for the accumulated base string offset when assigning a
new BTF base. This is required when the base is itself split.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261009112324.1442319-5-alan.maguire@oracle.com
This commit is contained in:
Alan Maguire 2026-10-09 12:23:21 +01:00 committed by Alexei Starovoitov
parent 672981f4ae
commit 5876080366
No known key found for this signature in database
5 changed files with 14 additions and 7 deletions
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5
include/linux/btf.h
View File

@ -608,7 +608,8 @@ struct btf_field_iter {
#ifdef CONFIG_BPF_SYSCALL
const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);
void btf_set_base_btf(struct btf *btf, const struct btf *base_btf);
int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **map_ids);
int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **map_ids,
__u32 **map_strs);
int btf_field_iter_init(struct btf_field_iter *it, struct btf_type *t,
enum btf_field_iter_kind iter_kind);
__u32 *btf_field_iter_next(struct btf_field_iter *it);
@ -682,7 +683,7 @@ static inline void btf_set_base_btf(struct btf *btf, const struct btf *base_btf)
}
static inline int btf_relocate(void *log, struct btf *btf, const struct btf *base_btf,
__u32 **map_ids)
__u32 **map_ids, __u32 **map_strs)
{
return -EOPNOTSUPP;
}

4
kernel/bpf/btf.c
View File

@ -1936,7 +1936,7 @@ void btf_set_base_btf(struct btf *btf, const struct btf *base_btf)
{
btf->base_btf = (struct btf *)base_btf;
btf->start_id = btf_nr_types(base_btf);
btf->start_str_off = base_btf->hdr.str_len;
btf->start_str_off = base_btf->start_str_off + base_btf->hdr.str_len;
}
static int env_resolve_init(struct btf_verifier_env *env)
@ -6997,7 +6997,7 @@ static struct btf *btf_parse_module(const char *module_name, const void *data,
goto errout;
if (base_btf != vmlinux_btf) {
err = btf_relocate(btf, vmlinux_btf, &btf->base_id_map);
err = btf_relocate(btf, vmlinux_btf, &btf->base_id_map, NULL);
if (err)
goto errout;
btf_free(base_btf);

2
tools/lib/bpf/btf.c
View File

@ -6640,7 +6640,7 @@ void btf_set_base_btf(struct btf *btf, const struct btf *base_btf)
int btf__relocate(struct btf *btf, const struct btf *base_btf)
{
int err = btf_relocate(btf, base_btf, NULL);
int err = btf_relocate(btf, base_btf, NULL, NULL);
if (!err)
btf->owns_base = false;

7
tools/lib/bpf/btf_relocate.c
View File

@ -441,7 +441,8 @@ static int btf_relocate_rewrite_strs(struct btf_relocate *r, __u32 i)
/* If successful, output of relocation is updated BTF with base BTF pointing
* at base_btf, and type ids, strings adjusted accordingly.
*/
int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **id_map)
int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **id_map,
__u32 **str_map)
{
unsigned int nr_types = btf__type_cnt(btf);
const struct btf_header *dist_base_hdr;
@ -512,6 +513,10 @@ int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **id_map)
*id_map = r.id_map;
r.id_map = NULL;
}
if (str_map) {
*str_map = r.str_map;
r.str_map = NULL;
}
err_out:
free(r.id_map);
free(r.str_map);

3
tools/lib/bpf/libbpf_internal.h
View File

@ -249,7 +249,8 @@ const char *btf_kind_str(const struct btf_type *t);
const struct btf_type *skip_mods_and_typedefs(const struct btf *btf, __u32 id, __u32 *res_id);
const struct btf_header *btf_header(const struct btf *btf);
void btf_set_base_btf(struct btf *btf, const struct btf *base_btf);
int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **id_map);
int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **id_map,
__u32 **str_map);
bool btf_type_is_traceable_func(const struct btf *btf, const struct btf_type *t);
static inline enum btf_func_linkage btf_func_linkage(const struct btf_type *t)