From: Alan Maguire <alan.maguire@oracle.com>
To: ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net,
eddyz87@gmail.com, jolsa@kernel.org
Cc: ihor.solodrai@linux.dev, yonghong.song@linux.dev,
song@kernel.org, qmo@kernel.org, martin.lau@linux.dev,
memxor@gmail.com, emil@etsalapatis.com, mcgrof@kernel.org,
petr.pavlu@suse.com, tj@kernel.org, kees@kernel.org,
nathan@kernel.org, arnd@arndb.de, puranjay@kernel.org,
yatsenko@meta.com, atenart@kernel.org, ojeda@kernel.org,
linux-modules@vger.kernel.org, arnaldo.melo@gmail.com,
bpf@vger.kernel.org, Alan Maguire <alan.maguire@oracle.com>
Subject: [PATCH v4 bpf-next 4/7] btf: Preserve string relocation maps for split BTF
Date: Fri, 9 Oct 2026 12:23:21 +0100 [thread overview]
Message-ID: <20261009112324.1442319-5-alan.maguire@oracle.com> (raw)
In-Reply-To: <20261009112324.1442319-1-alan.maguire@oracle.com>
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>
Assisted-by: OpenAI Codex (GPT-5.6)
---
include/linux/btf.h | 5 +++--
kernel/bpf/btf.c | 4 ++--
tools/lib/bpf/btf.c | 2 +-
tools/lib/bpf/btf_relocate.c | 7 ++++++-
tools/lib/bpf/libbpf_internal.h | 3 ++-
5 files changed, 14 insertions(+), 7 deletions(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index f731c7a5f14c..b66e20a18c54 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -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;
}
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 592b71a83841..22dd123450c3 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -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)
@@ -6994,7 +6994,7 @@ 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);
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 512b3962f75f..d2ff6f5d6d5b 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -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;
diff --git a/tools/lib/bpf/btf_relocate.c b/tools/lib/bpf/btf_relocate.c
index df5fa4bd87d6..e55dd75f6c95 100644
--- a/tools/lib/bpf/btf_relocate.c
+++ b/tools/lib/bpf/btf_relocate.c
@@ -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);
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 546f65b95cf4..4e45dfacb548 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -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)
--
2.43.5
next prev parent reply other threads:[~2026-10-09 11:24 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-09 11:23 [PATCH v4 bpf-next 0/7] kbuild, bpf: Support inline info in BTF Alan Maguire
2026-10-09 11:23 ` [PATCH v4 bpf-next 1/7] resolve_btfids: Build separate main and inline BTF objects Alan Maguire
2026-10-09 11:23 ` [PATCH v4 bpf-next 2/7] resolve_btfids: Populate BTF link section Alan Maguire
2026-10-09 12:24 ` bot+bpf-ci
2026-10-09 11:23 ` [PATCH v4 bpf-next 3/7] kbuild, btf: Expose vmlinux inline BTF through sysfs Alan Maguire
2026-10-09 11:23 ` Alan Maguire [this message]
2026-10-09 12:01 ` [PATCH v4 bpf-next 4/7] btf: Preserve string relocation maps for split BTF sashiko-bot
2026-10-09 14:00 ` Alan Maguire
2026-10-09 11:23 ` [PATCH v4 bpf-next 5/7] btf: Relocate and expose module inline BTF Alan Maguire
2026-10-09 11:23 ` [PATCH v4 bpf-next 6/7] selftests/bpf: Test BTF sysfs inline representations Alan Maguire
2026-10-09 12:25 ` sashiko-bot
2026-10-11 14:29 ` Alexei Starovoitov
2026-10-09 11:23 ` [PATCH v4 bpf-next 7/7] selftests/bpf: Add a test verifying inline information Alan Maguire
2026-10-09 12:33 ` sashiko-bot
2026-10-11 14:40 ` [PATCH v4 bpf-next 0/7] kbuild, bpf: Support inline info in BTF patchwork-bot+netdevbpf
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