Messages in this thread | | | From | Marco Elver <> | Date | Wed, 16 Sep 2020 10:46:41 +0200 | Subject | Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e |
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On Wed, 16 Sep 2020 at 10:30, <peterz@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 <ndesaulniers@google.com> wrote: > > > On Tue, Sep 15, 2020 at 10:21 AM Borislav Petkov <bp@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(), ...?).
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.
Thanks, -- Marco
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