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.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Fixes: 2d12c6fb7875 ("objtool: Remove ANNOTATE_IGNORE_ALTERNATIVE from CLAC/STAC")
Closes: https://lore.kernel.org/CAHk-=wi6goUT36sR8GE47_P-aVrd5g38=VTRHpktWARbyE-0ow@mail.gmail.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://patch.msgid.link/3d22415f7b8e06a64e0873b21f48389290eeaa49.1761767616.git.jpoimboe@kernel.org

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 620854fdaaf6333b9ceb6e64bf1ba52d4f1cc47b..9004fbc06769392175333238d4fb83f103ad4106 100644 (file)
--- 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;
 
        /*