linux-kernel - [PATCH] objtool/klp: Fix bug table handling for __WARN

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Message-ID: <a8e0a714b9da962858842b9aecd63b4900927c88.1769406850.git.jpoimboe@kernel.org>
Date: Sun, 25 Jan 2026 21:56:39 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org,
	Breno Leitao <leitao@...ian.org>,
	Puranjay Mohan <puranjay@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Song Liu <song@...nel.org>
Subject: [PATCH] objtool/klp: Fix bug table handling for __WARN_printf()

Running objtool klp-diff on a changed function which uses WARN() can
fail with:

  vmlinux.o: error: objtool: md_run+0x866: failed to convert reloc sym '__bug_table' to its proper format

The problem is that since commit 5b472b6e5bd9 ("x86_64/bug: Implement
__WARN_printf()"), each __WARN_printf() call site now directly
references its bug table entry.  klp-diff errors out when it can't
convert such section-based references to object symbols (because bug
table entries don't have symbols).

Luckily, klp-diff already has code to create symbols for bug table
entries.  Move that code earlier, before function diffing.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Fixes: 5b472b6e5bd9 ("x86_64/bug: Implement __WARN_printf()")
Reported-by: Song Liu <song@...nel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
For tip/objtool/urgent.

 tools/objtool/klp-diff.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index bb6b711d4e73..76aa77c26655 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1425,9 +1425,6 @@ static int clone_special_sections(struct elfs *e)
 {
 	struct section *patched_sec;
 
-	if (create_fake_symbols(e->patched))
-		return -1;
-
 	for_each_sec(e->patched, patched_sec) {
 		if (is_special_section(patched_sec)) {
 			if (clone_special_section(e, patched_sec))
@@ -1704,6 +1701,17 @@ int cmd_klp_diff(int argc, const char **argv)
 	if (!e.out)
 		return -1;
 
+	/*
+	 * Special section fake symbols are needed so that individual special
+	 * section entries can be extracted by clone_special_sections().
+	 *
+	 * Note the fake symbols are also needed by clone_included_functions()
+	 * because __WARN_printf() call sites add references to bug table
+	 * entries in the calling functions.
+	 */
+	if (create_fake_symbols(e.patched))
+		return -1;
+
 	if (clone_included_functions(&e))
 		return -1;
 
-- 
2.52.0