[tip: objtool/core] objtool/klp: Fix .kcfi_traps special section extraction

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     7df1638df97b2aaaff4731b72d4940053257c952
Gitweb:        https://git.kernel.org/tip/7df1638df97b2aaaff4731b72d4940053257c952
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Sat, 08 Aug 2026 16:17:05 -07:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Wed, 12 Aug 2026 13:52:07 -07:00

objtool/klp: Fix .kcfi_traps special section extraction

create_fake_symbols() creates a symbol per entry for special sections.
It does so in two steps: first for the sections which have
ANNOTATE_DATA_SPECIAL annotations, then for the rest, using entsize or
the reloc count to infer the entry size.  The second step skips the
sections already handled by the first one by looking for a symbol at
offset 0.

That heuristic is too fuzzy: with Clang and CONFIG_CFI, it misfires on
.kcfi_traps because Clang emits a .Ltmp* assembler-local label at the
start of the section, so no symbols are created and
clone_special_sections() extracts nothing.  klp-build still reports
SUCCESS, but the livepatch module has no __kcfi_traps section and the
traps for the patched functions are lost.

Look for the actual fake symbols created by the first step instead.

Fixes: da4326573ae8d ("objtool/klp: Fix kCFI trap handling")
Reported-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Closes: https://lore.kernel.org/r/akQNqlfFC0T5pcMa@xxxxxxxxxx
Acked-by: Song Liu <song@xxxxxxxxxx>
Link: https://patch.msgid.link/8faaead205b219607b6fc2359ae743be824056eb.1786230311.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/include/objtool/elf.h |  1 +
 tools/objtool/klp-diff.c            | 26 ++++++++++++++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index d9c44df..a82517a 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -97,6 +97,7 @@ struct symbol {
 	u8 included	     : 1;
 	u8 klp		     : 1;
 	u8 dont_correlate    : 1;
+	u8 fake		     : 1;
 	struct list_head pv_target;
 	struct reloc *relocs;
 	struct section *group_sec;
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index cdc63ab..a66049e 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1630,6 +1630,7 @@ static int create_fake_symbol(struct elf *elf, struct section *sec,
 			      unsigned long offset, size_t size)
 {
 	char name[SYM_NAME_LEN];
+	struct symbol *sym;
 	unsigned int type;
 	static int ctr;
 	char *c;
@@ -1646,7 +1647,24 @@ static int create_fake_symbol(struct elf *elf, struct section *sec,
 	 *	       while still allowing objdump to disassemble it.
 	 */
 	type = is_text_sec(sec) ? STT_NOTYPE : STT_OBJECT;
-	return elf_create_symbol(elf, name, sec, STB_LOCAL, type, offset, size) ? 0 : -1;
+
+	sym = elf_create_symbol(elf, name, sec, STB_LOCAL, type, offset, size);
+	if (!sym)
+		return -1;
+
+	sym->fake = 1;
+	return 0;
+}
+
+static bool has_fake_symbols(struct section *sec)
+{
+	struct symbol *sym;
+
+	sec_for_each_sym(sec, sym)
+		if (sym->fake)
+			return true;
+
+	return false;
 }
 
 /*
@@ -1738,7 +1756,11 @@ entsize:
 		unsigned int entry_size;
 		unsigned long offset;
 
-		if (!is_special_section(sec) || find_symbol_by_offset(sec, 0))
+		if (!is_special_section(sec))
+			continue;
+
+		/* Skip sections already handled by step 1 above */
+		if (has_fake_symbols(sec))
 			continue;
 
 		if (!sec->rsec) {