linux-kernel - Re: [PATCH v2 08/28] x86, build: use objtool mcount

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Message-ID: <202009031456.C058EC4@keescook>
Date:   Thu, 3 Sep 2020 14:58:28 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v2 08/28] x86, build: use objtool mcount

On Thu, Sep 03, 2020 at 01:30:33PM -0700, Sami Tolvanen wrote:
> Select HAVE_OBJTOOL_MCOUNT if STACK_VALIDATION is selected to use
> objtool to generate __mcount_loc sections for dynamic ftrace with
> Clang and gcc <5.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

Am I right to understand that this fixes mcount for Clang generally
(i.e. it's not _strictly_ related to LTO, though LTO depends on this
change)? And does this mean mcount was working for gcc < 5?

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook