[tip: objtool/urgent] objtool: Fix skip_alt_group() for non-alternative STAC/CLAC

["tip-bot2 for Josh Poimboeuf" <tip-bot2@linutronix.de>]

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

Commit-ID:     2c132efb3a443ab22f3b05e547ccc42bf2ee5abf
Gitweb:        https://git.kernel.org/tip/2c132efb3a443ab22f3b05e547ccc42bf2ee5abf
Author:        Josh Poimboeuf <jpoimboe@kernel.org>
AuthorDate:    Wed, 29 Oct 2025 12:54:08 -07:00
Committer:     Josh Poimboeuf <jpoimboe@kernel.org>
CommitterDate: Wed, 29 Oct 2025 21:23:49 -07:00

objtool: Fix skip_alt_group() for non-alternative STAC/CLAC

If an insn->alt points to a STAC/CLAC instruction, skip_alt_group()
assumes it's part of an alternative ("alt group") as opposed to some
other kind of "alt" such as an exception fixup.

While that assumption may hold true in the current code base, Linus has
an out-of-tree patch which breaks that assumption by replacing the
STAC/CLAC alternatives with raw STAC/CLAC instructions.

Make skip_alt_group() more robust by making sure it's actually an alt
group before continuing.

Fixes: 2d12c6fb7875 ("objtool: Remove ANNOTATE_IGNORE_ALTERNATIVE from CLAC/STAC")
Closes: https://lore.kernel.org/CAHk-=wi6goUT36sR8GE47_P-aVrd5g38=VTRHpktWARbyE-0ow@mail.gmail.com
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://patch.msgid.link/3d22415f7b8e06a64e0873b21f48389290eeaa49.1761767616.git.jpoimboe@kernel.org
---
 tools/objtool/check.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 620854f..9004fbc 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3516,8 +3516,11 @@ static bool skip_alt_group(struct instruction *insn)
 {
 	struct instruction *alt_insn = insn->alts ? insn->alts->insn : NULL;
 
+	if (!insn->alt_group)
+		return false;
+
 	/* ANNOTATE_IGNORE_ALTERNATIVE */
-	if (insn->alt_group && insn->alt_group->ignore)
+	if (insn->alt_group->ignore)
 		return true;
 
 	/*