[PATCH 14/48] objtool/klp: Fix extraction of text annotations for alternatives

Josh Poimboeuf
2026-04-23T04:04:30Z

Objtool is failing to extract text annotations which reference
.altinstr_replacement instructions:

1) Alternative replacement fake symbols are NOTYPE rather than FUNC,
and they don't have sym->included set, thus they aren't recognized
by should_keep_special_sym().

2) .discard.annotate_insn gets processed before .altinstr_replacement,
so the referenced (fake) symbols don't have clones yet.

Fix the first issue by checking for a valid clone instead of
sym->included and by accepting NOTYPE symbols when processing
.discard.annotate_insn.

Fix the second issue by deferring text annotation processing until after
the other special sections have been cloned.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
tools/objtool/klp-diff.c | 33 ++++++++++++++++++++++++++++-----
1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 3303664a39d7..22942f394745 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1452,6 +1452,7 @@ static int create_fake_symbols(struct elf *elf)
/* Keep a special section entry if it references an included function */
static bool should_keep_special_sym(struct elf *elf, struct symbol *sym)
{
+ bool annotate_insn = !strcmp(sym->sec->name, ".discard.annotate_insn");
struct reloc *reloc;

if (is_sec_sym(sym) || !sym->sec->rsec)
@@ -1461,7 +1462,16 @@ static bool should_keep_special_sym(struct elf *elf, struct symbol *sym)
if (convert_reloc_sym(elf, reloc))
continue;

- if (is_func_sym(reloc->sym) && reloc->sym->included)
+ if (!reloc->sym->clone || is_undef_sym(reloc->sym->clone))
+ continue;
+
+ /*
+ * Keep special section references to cloned functions.
+ * In some cases annotate_insn can also reference cloned alt
+ * replacement fake symbols; keep those references as well.
+ */
+ if (is_func_sym(reloc->sym) ||
+ (annotate_insn && is_notype_sym(reloc->sym)))
return true;
}

@@ -1605,15 +1615,28 @@ static int clone_special_section(struct elfs *e, struct section *patched_sec)
/* Extract only the needed bits from special sections */
static int clone_special_sections(struct elfs *e)
{
- struct section *patched_sec;
+ struct section *sec, *annotate_insn = NULL;

- for_each_sec(e->patched, patched_sec) {
- if (is_special_section(patched_sec)) {
- if (clone_special_section(e, patched_sec))
+ for_each_sec(e->patched, sec) {
+ if (is_special_section(sec)) {
+ if (!strcmp(sec->name, ".discard.annotate_insn")) {
+ annotate_insn = sec;
+ continue;
+ }
+ if (clone_special_section(e, sec))
return -1;
}
}

+ /*
+ * Do .discard.annotate_insn last, it can reference other special
+ * sections (alt replacements) so they need to be cloned first.
+ */
+ if (annotate_insn) {
+ if (clone_special_section(e, annotate_insn))
+ return -1;
+ }
+
return 0;
}

--
2.53.0