From 023f2340f053537cce170c31c430b0886c6f07ca Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 3 Nov 2022 20:57:51 +0100 Subject: [PATCH] objtool: Fix weak hole vs prefix symbol Boris (and the robot) reported that objtool grew a new complaint about unreachable instructions. Upon inspection it was immediately clear the __weak zombie instructions struck again. For the unweary, the linker will simply remove the symbol for overriden __weak symbols but leave the instructions in place, creating unreachable instructions -- and objtool likes to report these. Commit 4adb23686795 ("objtool: Ignore extra-symbol code") was supposed to have dealt with that, but the new commit 9f2899fe36a6 ("objtool: Add option to generate prefix symbols") subtly broke that logic by created unvisited symbols. Fixes: 9f2899fe36a6 ("objtool: Add option to generate prefix symbols") Reported-by: Borislav Petkov Reported-by: kernel test robot Signed-off-by: Peter Zijlstra (Intel) --- tools/objtool/check.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 55066c493570..4f1a7384426b 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -4053,8 +4053,28 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func, offset = func->offset - prev->offset; if (offset >= opts.prefix) { - if (offset == opts.prefix) + if (offset == opts.prefix) { + /* + * Since the sec->symbol_list is ordered by + * offset (see elf_add_symbol()) the added + * symbol will not be seen by the iteration in + * validate_section(). + * + * Hence the lack of list_for_each_entry_safe() + * there. + * + * The direct concequence is that prefix symbols + * don't get visited (because pointless), except + * for the logic in ignore_unreachable_insn() + * that needs the terminating insn to be visited + * otherwise it will report the hole. + * + * Hence mark the first instruction of the + * prefix symbol as visisted. + */ + prev->visited |= VISITED_BRANCH; elf_create_prefix_symbol(file->elf, func, opts.prefix); + } break; } insn = prev;