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

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Message-ID: <20210602101521.GD30436@shell.armlinux.org.uk>
Date:   Wed, 2 Jun 2021 11:15:21 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Mike Rapoport <rppt@...ux.ibm.com>
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 Wed, Jun 02, 2021 at 11:33:10AM +0300, Mike Rapoport wrote:
> 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.

You can not assume that all sections will be between these symbols. This
isn't specific to 32-bit ARM. If you look at x86's vmlinux.lds.in, you
will see that BUG_TABLE and ORC_UNWIND_TABLE are after _edata, along
with many other undiscarded sections before __bss_start. So it seems
your assumptions in trying to clean this up are somewhat false.

-- 
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