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Wed, 16 Sep 2020 05:33:55 -0400 Received: from mail-ot1-x32c.google.com (mail-ot1-x32c.google.com [IPv6:2607:f8b0:4864:20::32c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EF8FDC06174A for ; Wed, 16 Sep 2020 02:33:54 -0700 (PDT) Received: by mail-ot1-x32c.google.com with SMTP id m12so6100444otr.0 for ; Wed, 16 Sep 2020 02:33:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=+69jB+wV3csf3KfbgPgpUDFiF1twt7Lc/K19h4NVXE8=; b=b9Tdi+x3m6RjXww5amVy4aWTXdBdze1nTwb8XGuGV06W6ssFDtYxk5tOh0IAs+vI0Y pEHO57Y6fkVbSK4Ucx5uW5zvUOHYxvQivuHXQkmDzF7HhdM0zZy/lKQVTEz0ecIwJqCj Ahq1ISaVydDGOpELkgZPJjIQN89s2A+N2H+HDwuxbZ9aewtS873PRzyq+1tOaeSRSKmu JyoSGYx0QzjA/oOG1Ozo8FoKAUYpOWemYOMlsULJXG843jt+DqIPZBXk1lO0FG7BNlMR bj470I6zMi+EnFyw5J34CTEfeRWJKpaQFKUo98HgBOEs8GeFK0LNJ7niaAOa0tPkiK5w hsFg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=+69jB+wV3csf3KfbgPgpUDFiF1twt7Lc/K19h4NVXE8=; b=N5pimmIbpNuhBkUyF3w753VN3H4kAG+W0BoiWiL7nk6f/90wz+hu0UScleFdsQxpeb 0obRgQD6eOrZfdGs/6RbiOQpDwzldnjecr+hQQMWL4QH1RPKZ8m1YURQKlYMgui8meTT Tag7hUbV/y194S2mTlZMFH8U9/WCSJCvPd6+kLTxMvwtnxWc14fgAeDuLGUA6SstGduZ 3WGi/8iIlsiJ1rvIlaJrExnsQtU/pIPwKWMXbnp9BRB0a9WPsVjJIFLLBxxBWPBZV3Gp BiDoJqSA+ppA/RVQ+SQcLbqxsipVgJ7JFpV2b3Ocjy/+kIkJqMK+RQIVHrhSjPd2iGBP h8gg== X-Gm-Message-State: AOAM532FlBxVfcvoMB8pURIDyhE4XIWnRmHqEIZYRLjm/os0miQnAl/b 7ML5/Y+mZE/EFizC3YAJvM/TTYpYYVm75wWBIKC+fQ== X-Google-Smtp-Source: ABdhPJzC3u0MfC7SFCZfdqlXndJgQubQG3xmNxCc/hFWxahQxzm9mxqCA8rt3vIszhKN4told+dhXtlQUN8VFgjYRjw= X-Received: by 2002:a9d:758b:: with SMTP id s11mr14889445otk.251.1600248832924; Wed, 16 Sep 2020 02:33:52 -0700 (PDT) MIME-Version: 1.0 References: <5f60c4e0.Ru0MTgSE9A7mqhpG%lkp@intel.com> <20200915135519.GJ14436@zn.tnic> <20200915141816.GC28738@shao2-debian> <20200915160554.GN14436@zn.tnic> <20200915170248.gcv54pvyckteyhk3@treble> <20200915172152.GR14436@zn.tnic> <20200916083032.GL2674@hirez.programming.kicks-ass.net> <20200916090620.GN2674@hirez.programming.kicks-ass.net> In-Reply-To: <20200916090620.GN2674@hirez.programming.kicks-ass.net> From: Marco Elver Date: Wed, 16 Sep 2020 11:33:41 +0200 Message-ID: Subject: Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e To: Peter Zijlstra Cc: Josh Poimboeuf , Borislav Petkov , Nick Desaulniers , Rong Chen , kernel test robot , "Li, Philip" , x86-ml , LKML , clang-built-linux , Andrew Morton , Kees Cook , Masahiro Yamada , kasan-dev Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 16 Sep 2020 at 11:06, wrote: > On Wed, Sep 16, 2020 at 10:46:41AM +0200, Marco Elver wrote: > > On Wed, 16 Sep 2020 at 10:30, wrote: > > > On Tue, Sep 15, 2020 at 08:09:16PM +0200, Marco Elver wrote: > > > > On Tue, 15 Sep 2020 at 19:40, Nick Desaulniers wrote: > > > > > On Tue, Sep 15, 2020 at 10:21 AM Borislav Petkov 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. That's fair, and I would also prefer a proper fix. :-) > > 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. If it's a bug in current compilers, it'll be hard to get the fix into those. My suspicion is there's a bug somewhere. We can try to make new compiler versions do the right thing. Or maybe we're just missing some flags, which would be nice. I'll investigate some more. Thanks, -- Marco