linux-kernel - Re: [PATCH 3/6] tracing: Wrap section comparison in tracer_alloc_buffers with COMPARE

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Message-ID: <20200219144333.1ce3f9ea@gandalf.local.home>
Date:   Wed, 19 Feb 2020 14:43:33 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH 3/6] tracing: Wrap section comparison in
 tracer_alloc_buffers with COMPARE_SECTIONS

On Wed, 19 Feb 2020 12:22:49 -0700
Nathan Chancellor <natechancellor@...il.com> wrote:

> Yes, thank you for the analysis and further discussion! I have done some
> rudimentary printk debugging in QEMU and it looks like these are produce
> the same value:
> 
> __stop___trace_bprintk_fmt
> &__stop___trace_bprintk_fmt
> &__start___trace_bprintk_fmt[0]
> 
> as well as
> 
> __stop___trace_bprintk_fmt != __start___trace_bprintk_fmt
> &__stop___trace_bprintk_fmt != &__start___trace_bprintk_fmt
> &__stop___trace_bprintk_fmt[0] != &__start___trace_bprintk_fmt[0]
> 
> I'll use the second one once I confirm this is true in all callspots
> with both Clang and GCC, since it looks cleaner. Let me know if there
> are any objections to that.

Myself and I'm sure others would be fine with this approach as it is
still readable. I was just against the encapsulating the logic in a
strange macro that killed readability.

I haven't looked at the resulting assembly from these, and will
currently take your word for it ;-)  Of course, I will thoroughly test
any patches to this code to make sure it does not hurt functionality.

-- Steve