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Date:   Wed, 27 May 2020 20:05:22 +0800
From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc:     linux-mips@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Borislav Petkov <bp@suse.de>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Fangrui Song <maskray@google.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/3] MIPS: Move kernel head into a standalone section
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On Wed, 27 May 2020 13:53:54 +0200
Thomas Bogendoerfer <tsbogend@alpha.franken.de> wrote:

> On Wed, May 27, 2020 at 02:34:33PM +0800, Jiaxun Yang wrote:
> > That's what already done by Arm64 and other architectures.
> > That would allow us put more things like PE headers safely into
> > the header.
> > 
> > Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> > ---
> >  arch/mips/kernel/head.S        | 4 ++--
> >  arch/mips/kernel/vmlinux.lds.S | 8 ++++++--
> >  2 files changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/mips/kernel/head.S b/arch/mips/kernel/head.S
> > index c7c2795837e7..8081a905a71c 100644
> > --- a/arch/mips/kernel/head.S
> > +++ b/arch/mips/kernel/head.S
> > @@ -59,6 +59,8 @@
> >  #endif
> >  	.endm
> >  
> > +	__HEAD
> > +_head:
> >  #ifndef CONFIG_NO_EXCEPT_FILL
> >  	/*
> >  	 * Reserved space for exception handlers.  
> 
> I'm adding the missing piece, why this change ist broken:
> 
>          * Necessary for machines which link their kernels at KSEG0.
> 
> by putting something in front of that will probably break platforms
> making use of "feature". If we can make sure, we don't need it
> anymore, we should first remove this and then add __HEAD part.

__HEAD is just marking the section of code.
It will not add anything to the binary.

Btw: I just noticed this patch may break relocatable kernel. I'll delay
it for next merge window.

Thanks.

> 
> Thomas.
> 

--
Jiaxun Yang