linux-kernel - Re: [RFC/RFT PATCH 2/5] memblock: introduce generic memblock_setup

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Date:   Wed, 2 Jun 2021 11:33:10 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org
Subject: Re: [RFC/RFT PATCH 2/5] memblock: introduce generic
 memblock_setup_resources()

On Tue, Jun 01, 2021 at 02:54:15PM +0100, Russell King (Oracle) wrote:
> On Mon, May 31, 2021 at 03:29:56PM +0300, Mike Rapoport wrote:
> > +	code_resource.start = __pa_symbol(_text);
> > +	code_resource.end = __pa_symbol(_etext)-1;
> > +	rodata_resource.start = __pa_symbol(__start_rodata);
> > +	rodata_resource.end = __pa_symbol(__end_rodata)-1;
> > +	data_resource.start = __pa_symbol(_sdata);
> > +	data_resource.end = __pa_symbol(_edata)-1;
> > +	bss_resource.start = __pa_symbol(__bss_start);
> > +	bss_resource.end = __pa_symbol(__bss_stop)-1;
> 
> This falls short on 32-bit ARM. The old code was:
> 
> -       kernel_code.start   = virt_to_phys(_text);
> -       kernel_code.end     = virt_to_phys(__init_begin - 1);
> -       kernel_data.start   = virt_to_phys(_sdata);                             
> -       kernel_data.end     = virt_to_phys(_end - 1);                           
> 
> If I look at one of my kernels:
> 
> c0008000 T _text
> c0b5b000 R __end_rodata
> ... exception and unwind tables live here ...
> c0c00000 T __init_begin
> c0e00000 D _sdata
> c0e68870 D _edata
> c0e68870 B __bss_start
> c0e995d4 B __bss_stop
> c0e995d4 B _end
> 
> So the original covers _text..__init_begin-1 which includes the
> exception and unwind tables. Your version above omits these, which
> leaves them exposed.

Right, this needs to be fixed. Is there any reason the exception and unwind
tables cannot be placed between _sdata and _edata? 

It seems to me that they were left outside for purely historical reasons.
Commit ee951c630c5c ("ARM: 7568/1: Sort exception table at compile time")
moved the exception tables out of .data section before _sdata existed.
Commit 14c4a533e099 ("ARM: 8583/1: mm: fix location of _etext") moved
_etext before the unwind tables and didn't bother to put them into data or
rodata areas.

-- 
Sincerely yours,
Mike.