linux-kernel - Re: [PATCH 1/2] x86/boot: move early_serial

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Message-ID: <20190507082808.GB125993@gmail.com>
Date:   Tue, 7 May 2019 10:28:08 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Pingfan Liu <kernelfans@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Kees Cook <keescook@...omium.org>
Cc:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jordan Borgner <mail@...dan-borgner.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/boot: move early_serial_base to .data section


* Pingfan Liu <kernelfans@...il.com> wrote:

> arch/x86/boot/compressed/head_64.S clears BSS after relocated. If early
> serial is set up before clearing BSS, the early_serial_base will be reset
> to 0.
> 
> Initializing early_serial_base as -1 to push it to .data section.

I'm wondering whether it's wise to clear the BSS after relocation to 
begin with. It already gets cleared once, and an implicit zeroing of all 
fields on kernel relocation sounds dubious to me.

Is there a strong reason for that? I.e. is there some uninitialized or 
otherwise important-to-clear data there?

Thanks,

	Ingo