On Wed, Sep 16, 2020 at 10:46:41AM +0200, Marco Elver wrote: > On Wed, 16 Sep 2020 at 10:30, <pet...@infradead.org> wrote: > > On Tue, Sep 15, 2020 at 08:09:16PM +0200, Marco Elver wrote: > > > On Tue, 15 Sep 2020 at 19:40, Nick Desaulniers <ndesaulni...@google.com> > > > wrote: > > > > On Tue, Sep 15, 2020 at 10:21 AM Borislav Petkov <b...@alien8.de> wrote: > > > > > > > init/calibrate.o: warning: objtool: asan.module_ctor()+0xc: call > > > > > without frame pointer save/setup > > > > > init/calibrate.o: warning: objtool: asan.module_dtor()+0xc: call > > > > > without frame pointer save/setup > > > > > init/version.o: warning: objtool: asan.module_ctor()+0xc: call > > > > > without frame pointer save/setup > > > > > init/version.o: warning: objtool: asan.module_dtor()+0xc: call > > > > > without frame pointer save/setup > > > > > certs/system_keyring.o: warning: objtool: asan.module_ctor()+0xc: > > > > > call without frame pointer save/setup > > > > > certs/system_keyring.o: warning: objtool: asan.module_dtor()+0xc: > > > > > call without frame pointer save/setup > > > > > > This one also appears with Clang 11. This is new I think because we > > > started emitting ASAN ctors for globals redzone initialization. > > > > > > I think we really do not care about precise stack frames in these > > > compiler-generated functions. So, would it be reasonable to make > > > objtool ignore all *san.module_ctor and *san.module_dtor functions (we > > > have them for ASAN, TSAN, MSAN)? > > > > The thing is, if objtool cannot follow, it cannot generate ORC data and > > our unwinder cannot unwind through the instrumentation, and that is a > > fail. > > > > Or am I missing something here? > > They aren't about the actual instrumentation. The warnings are about > module_ctor/module_dtor functions which are compiler-generated, and > these are only called on initialization/destruction (dtors only for > modules I guess). > > E.g. for KASAN it's the calls to __asan_register_globals that are > called from asan.module_ctor. For KCSAN the tsan.module_ctor is > effectively a noop (because __tsan_init() is a noop), so it really > doesn't matter much. > > Is my assumption correct that the only effect would be if something > called by them fails, we just don't see the full stack trace? I think > we can live with that, there are only few central places that deal > with ctors/dtors (do_ctors(), ...?).
Not only fails, lockdep for example likes to store stack traces of various callsites etc.. Also perf (NMI) likes to think it can unwind at all times. > The "real" fix would be to teach the compilers about "frame pointer > save/setup" for generated functions, but I don't think that's > realistic. How is that unrealistic? If you build with framepointers enabled, the compiler is supposed to know about this stuff.
