linux-kernel - Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

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Date:   Mon, 9 Nov 2020 20:48:01 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Jann Horn <jannh@...gle.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v6 22/25] x86/asm: annotate indirect jumps

On Mon, Nov 9, 2020 at 6:29 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> How would I recreate all these warnings?

You can reproduce all of these using a normal gcc build without any of
the LTO patches by running objtool check -arfld vmlinux.o. However,
with gcc you'll see even more warnings due to duplicate symbol names,
as Peter pointed out elsewhere in the thread, so I looked at only the
warnings that objtool also prints with LTO.

Note that the LTO series contains a patch to split noinstr validation
from --vmlinux, as we need to run objtool here even if
CONFIG_VMLINUX_VALIDATION isn't selected, so I have not looked at the
noinstr warnings. The latest LTO tree is available here:

https://github.com/samitolvanen/linux/commits/clang-lto

> Here's the patch for hopefully making the warnings more helpful:

Thanks, I'll give it a try.

Sami