From: Josh Poimboeuf jpoimboe@redhat.com
commit 99033461e685b48549ec77608b4bda75ddf772ce upstream.
Objtool detection of asm jump tables would normally just work, except for the fact that asm retpolines use alternatives. Objtool thinks the alternative code path (a jump to the retpoline) is a sibling call.
Don't treat alternative indirect branches as sibling calls when the original instruction has a jump table.
Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Tested-by: Ard Biesheuvel ardb@kernel.org Acked-by: Ard Biesheuvel ardb@kernel.org Tested-by: Sami Tolvanen samitolvanen@google.com Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Acked-by: Herbert Xu herbert@gondor.apana.org.au Link: https://lore.kernel.org/r/460cf4dc675d64e1124146562cabd2c05aa322e8.161418241... Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- tools/objtool/check.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
--- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -107,6 +107,18 @@ static struct instruction *prev_insn_sam for (insn = next_insn_same_sec(file, insn); insn; \ insn = next_insn_same_sec(file, insn))
+static bool is_jump_table_jump(struct instruction *insn) +{ + struct alt_group *alt_group = insn->alt_group; + + if (insn->jump_table) + return true; + + /* Retpoline alternative for a jump table? */ + return alt_group && alt_group->orig_group && + alt_group->orig_group->first_insn->jump_table; +} + static bool is_sibling_call(struct instruction *insn) { /* @@ -119,7 +131,7 @@ static bool is_sibling_call(struct instr
/* An indirect jump is either a sibling call or a jump to a table. */ if (insn->type == INSN_JUMP_DYNAMIC) - return list_empty(&insn->alts); + return !is_jump_table_jump(insn);
/* add_jump_destinations() sets insn->call_dest for sibling calls. */ return (is_static_jump(insn) && insn->call_dest);