[PATCH bpf-next 1/3] bpf: Teach resolve_btfids about the setsc type
From: Chengkaitao
Date: Fri Apr 03 2026 - 13:09:58 EST
From: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
Add .BTF_ids.##sfx subsections under the .BTF_ids output section. The
number of entries in each .BTF_ids.##sfx subsection is derived from
(__BTF_ids_seg_end_##sfx - sym.st_value). With this, resolve_btfids
no longer relies on BTF_SET_END(). That allows kernel code to avoid
forcing symbols with similar properties to sit strictly between
BTF_SET_START and BTF_SET_END, and it sets the stage for refactoring
the BTF_SET* and BTF_ID* macros later.
Signed-off-by: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
---
include/asm-generic/btf_ids.lds.h | 23 ++++++++
include/asm-generic/vmlinux.lds.h | 2 +
tools/bpf/resolve_btfids/main.c | 89 +++++++++++++++++++++++++++++--
3 files changed, 111 insertions(+), 3 deletions(-)
create mode 100644 include/asm-generic/btf_ids.lds.h
diff --git a/include/asm-generic/btf_ids.lds.h b/include/asm-generic/btf_ids.lds.h
new file mode 100644
index 000000000000..7579ba58f5ff
--- /dev/null
+++ b/include/asm-generic/btf_ids.lds.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2026 KylinSoft Corporation.
+ * Copyright (c) 2026 Kaitao Cheng <chengkaitao@xxxxxxxxxx>
+ */
+#ifndef __ASM_GENERIC_BTF_IDS_LDS_H
+#define __ASM_GENERIC_BTF_IDS_LDS_H
+
+/*
+ * Linker script helpers for CONFIG_DEBUG_INFO_BTF .BTF_ids subsections.
+ * Input section .BTF_ids.##sfx must match __BTF_IDS_SUBSEC(sfx) in btf_ids.h.
+ */
+#ifdef CONFIG_DEBUG_INFO_BTF
+
+#define BTF_IDS_SUBSEG(sfx) \
+ KEEP(*(.BTF_ids.##sfx)) \
+ __BTF_ids_seg_end_##sfx = .;
+
+#define BTF_IDS_VERIFIER_SUBSEGS
+
+#endif /* CONFIG_DEBUG_INFO_BTF */
+
+#endif /* __ASM_GENERIC_BTF_IDS_LDS_H */
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 1e1580febe4b..96407498629e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -51,6 +51,7 @@
*/
#include <asm-generic/codetag.lds.h>
+#include <asm-generic/btf_ids.lds.h>
#ifndef LOAD_OFFSET
#define LOAD_OFFSET 0
@@ -691,6 +692,7 @@
. = ALIGN(PAGE_SIZE); \
.BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) { \
*(.BTF_ids) \
+ BTF_IDS_VERIFIER_SUBSEGS \
}
#else
#define BTF
diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
index f8a91fa7584f..d9b0c9c25eda 100644
--- a/tools/bpf/resolve_btfids/main.c
+++ b/tools/bpf/resolve_btfids/main.c
@@ -89,6 +89,7 @@
#define BTF_FUNC "func"
#define BTF_SET "set"
#define BTF_SET8 "set8"
+#define BTF_SETSC "setsc"
#define ADDR_CNT 100
@@ -104,7 +105,8 @@ enum btf_id_kind {
BTF_ID_KIND_NONE,
BTF_ID_KIND_SYM,
BTF_ID_KIND_SET,
- BTF_ID_KIND_SET8
+ BTF_ID_KIND_SET8,
+ BTF_ID_KIND_SETSC,
};
struct btf_id {
@@ -309,6 +311,77 @@ static int get_id(const char *prefix_end, char *buf, size_t buf_sz)
return 0;
}
+static int elf_sym_value_by_name(struct object *obj, const char *sym_name,
+ GElf_Addr *val)
+{
+ Elf_Scn *scn = NULL;
+ GElf_Shdr sh;
+ int n, i;
+
+ scn = elf_getscn(obj->efile.elf, obj->efile.symbols_shndx);
+ if (!scn || gelf_getshdr(scn, &sh) != &sh)
+ return -1;
+
+ n = sh.sh_size / sh.sh_entsize;
+ for (i = 0; i < n; i++) {
+ GElf_Sym sym;
+ char *name;
+
+ if (!gelf_getsym(obj->efile.symbols, i, &sym))
+ return -1;
+ if (sym.st_shndx == SHN_UNDEF)
+ continue;
+ name = elf_strptr(obj->efile.elf, obj->efile.strtabidx,
+ sym.st_name);
+ if (name && !strcmp(name, sym_name)) {
+ *val = sym.st_value;
+ return 0;
+ }
+ }
+ return -1;
+}
+
+/*
+ * BTF_ID_KIND_SETSC: begin is __BTF_ID__setsc__<name> (sym.st_value); end is
+ * __BTF_ids_seg_end_<name> from the linker script (btf_ids.lds.h).
+ */
+static int scatter_set_cnt_from_seg(struct object *obj, struct btf_id *id,
+ GElf_Addr begin)
+{
+ GElf_Addr end;
+ char sym_end[KSYM_NAME_LEN];
+ int cnt;
+
+ if (snprintf(sym_end, sizeof(sym_end), "__BTF_ids_seg_end_%s",
+ id->name) >= (int)sizeof(sym_end)) {
+ pr_err("FAILED scatter set symbol name overflow: %s\n", id->name);
+ return -1;
+ }
+
+ if (elf_sym_value_by_name(obj, sym_end, &end)) {
+ pr_err("FAILED scatter set %s: missing %s in %s\n",
+ id->name, sym_end, obj->path);
+ return -1;
+ }
+
+ if (end <= begin || (end - begin) % sizeof(int)) {
+ pr_err("FAILED scatter set %s: bad span (begin %#lx .. end %s %#lx)\n",
+ id->name, (unsigned long)begin, sym_end, (unsigned long)end);
+ return -1;
+ }
+
+ cnt = (int)((unsigned long)(end - begin) / sizeof(int) - 1);
+ if (cnt < 0) {
+ pr_err("FAILED scatter set %s: negative cnt\n", id->name);
+ return -1;
+ }
+ id->cnt = cnt;
+ pr_debug("scatter set %s cnt %d span %lu\n", id->name, cnt,
+ (unsigned long)(end - begin));
+
+ return 0;
+}
+
static struct btf_id *add_set(struct object *obj, char *name, enum btf_id_kind kind)
{
int len = strlen(name);
@@ -327,6 +400,9 @@ static struct btf_id *add_set(struct object *obj, char *name, enum btf_id_kind k
case BTF_ID_KIND_SET8:
prefixlen = sizeof(BTF_SET8 "__") - 1;
break;
+ case BTF_ID_KIND_SETSC:
+ prefixlen = sizeof(BTF_SETSC "__") - 1;
+ break;
default:
pr_err("Unexpected kind %d passed to %s() for symbol %s\n", kind, __func__, name);
return NULL;
@@ -549,6 +625,11 @@ static int symbols_collect(struct object *obj)
*/
if (id)
id->cnt = sym.st_size / sizeof(uint64_t) - 1;
+ /* setsc */
+ } else if (!strncmp(prefix, BTF_SETSC, sizeof(BTF_SETSC) - 1)) {
+ id = add_set(obj, prefix, BTF_ID_KIND_SETSC);
+ if (id && scatter_set_cnt_from_seg(obj, id, sym.st_value))
+ return -1;
/* set */
} else if (!strncmp(prefix, BTF_SET, sizeof(BTF_SET) - 1)) {
id = add_set(obj, prefix, BTF_ID_KIND_SET);
@@ -690,8 +771,9 @@ static int id_patch(struct object *obj, struct btf_id *id)
int *ptr = data->d_buf;
int i;
- /* For set, set8, id->id may be 0 */
- if (!id->id && id->kind != BTF_ID_KIND_SET && id->kind != BTF_ID_KIND_SET8) {
+ /* For set, set8, setsc, id->id may be 0 */
+ if (!id->id && id->kind != BTF_ID_KIND_SET &&
+ id->kind != BTF_ID_KIND_SET8 && id->kind != BTF_ID_KIND_SETSC) {
pr_err("WARN: resolve_btfids: unresolved symbol %s\n", id->name);
warnings++;
}
@@ -766,6 +848,7 @@ static int sets_patch(struct object *obj)
switch (id->kind) {
case BTF_ID_KIND_SET:
+ case BTF_ID_KIND_SETSC:
set = data->d_buf + off;
cnt = set->cnt;
qsort(set->ids, set->cnt, sizeof(set->ids[0]), cmp_id);
--
2.43.0