linux-kernel - Re: [PATCH v4 04/29] objtool: Add a pass for generating __mcount

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Message-ID: <alpine.LSU.2.21.2010011504340.6689@pobox.suse.cz>
Date:   Thu, 1 Oct 2020 15:17:07 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Sami Tolvanen <samitolvanen@...gle.com>
cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.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@...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, jthierry@...hat.com, jpoimboe@...hat.com
Subject: Re: [PATCH v4 04/29] objtool: Add a pass for generating
 __mcount_loc

Hi Sami,

On Tue, 29 Sep 2020, Sami Tolvanen wrote:

> From: Peter Zijlstra <peterz@...radead.org>
> 
> Add the --mcount option for generating __mcount_loc sections
> needed for dynamic ftrace. Using this pass requires the kernel to
> be compiled with -mfentry and CC_USING_NOP_MCOUNT to be defined
> in Makefile.
> 
> Link: https://lore.kernel.org/lkml/20200625200235.GQ4781@hirez.programming.kicks-ass.net/
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> [Sami: rebased to mainline, dropped config changes, fixed to actually use
>        --mcount, and wrote a commit message.]
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>

I am sorry to reply on v4. Should have been sooner.

Julien has been sending patches to make objtool's check functionality 
arch-agnostic as much as possible. So it seems to me that the patch should 
be based on the effort

I also wonder about making 'mcount' command separate from 'check'. Similar 
to what is 'orc' now. But that could be done later.

See tip-tree/objtool/core for both.

Thanks
Miroslav