linux-kernel - Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e

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Date:   Tue, 15 Sep 2020 20:09:16 +0200
From:   Marco Elver <elver@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Rong Chen <rong.a.chen@...el.com>,
        kernel test robot <lkp@...el.com>,
        "Li, Philip" <philip.li@...el.com>, x86-ml <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e

On Tue, 15 Sep 2020 at 19:40, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> On Tue, Sep 15, 2020 at 10:21 AM Borislav Petkov <bp@...en8.de> wrote:
> >
> > On Tue, Sep 15, 2020 at 12:02:48PM -0500, Josh Poimboeuf wrote:
> > > If somebody can share the .o file, I can take a look.
> >
> > If only I could reproduce...
> >
> > So I built:
> >
> > /home/share/src/llvm/tc-build/install/bin/clang-12 --version
> > ClangBuiltLinux clang version 12.0.0 (https://github.com/llvm/llvm-project 74a9c6d7e1c49cd0e3a8e8072b8aa03f7a84caff)
> > Target: x86_64-unknown-linux-gnu
> > Thread model: posix
> > InstalledDir: /home/share/src/llvm/tc-build/install/bin
> >
> > and I don't trigger that warning even with that compiler.
> >
> > What I do get is a lot of those pairs:
> >
> > 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)?

Thanks,
-- Marco