linux-kernel - Re: [PATCH] Add non-zero module sections to sysfs

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Message-ID: <BLU0-SMTP23C8D54498C7DFACDF083B97DB0@phx.gbl>
Date:	Sat, 6 Apr 2013 11:16:19 -0400
From:	John David Anglin <dave.anglin@...l.net>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Sebastian Wankerl <sisewank@....cs.fau.de>,
	linux-kernel@...r.kernel.org,
	Philip Kranz <philip.kranz@...glemail.com>,
	i4passt@...ts.informatik.uni-erlangen.de,
	linux-parisc@...r.kernel.org, corbet@....net
Subject: Re: [PATCH] Add non-zero module sections to sysfs

On 6-Apr-13, at 6:52 AM, James Bottomley wrote:

> On Sat, 2013-04-06 at 15:22 +1030, Rusty Russell wrote:
>>> The problem is our assumption that section names be unique.  This
>>> assumption is wrong.  The ELF spec says (version 1.1 page 1-15): "An
>>> object file may have more than one section with the same name."   
>>> We need
>>> to fix the kernel not to rely on a bogus assumption ... but we had  
>>> no
>>> idea how to do that in a way that preserved the backwards  
>>> compatibility
>>> of sections subdirectory.
>>>
>>> I admit that 35dead4235e2b67da7275b4122fed37099c2f462 is a hack,  
>>> but now
>>> the problem has got attention, can we fix it properly?
>>
>> Yep.  The original patch didn't go through me, or we would have had  
>> this
>> discussion back then...
>>
>> The use of section names in sysfs goes back to one Mr. Corbet.  Why  
>> did
>> he do it that way?  Because gdb's add-symbol-file makes the same
>> assumption.  So if we fixed the sysfs somehow, it still wouldn't be
>> useful, since there's no way to tell gdb :(
>>
>> The real answer don't use -ffunction-sections on modules: probably  
>> not
>> as important as the rest of the kernel.  And the new shiny is
>> -flto anyway.
>>
>> And that leaves us with a PA-RISC specific issue, for which we should
>> move the fix to PA-RISC.
>>
>> Thoughts?
>
> Well, we don't have much of a choice.  Our ELF stub jump on 32 bits  
> is a
> PCREL17.  That means once a module size is over 128k there's a  
> chance we
> might not be able to link it because the jump is too big for the
> instruction.  IPV6 is one such big module today, but I'm sure there  
> are
> others.  The only way I know to fix this is to allow the linker to
> insert stubs between functions, so we only fail at linking if a single
> function is >128k big.  The way to do this is -ffunction-sections,
> unless there's something else we could do (all we really need is a way
> to ensure we can insert ELF stubs every 128k).

There is now a config work around for this.  See:
http://www.spinics.net/lists/linux-parisc/msg04521.html

Dave
--
John David Anglin	dave.anglin@...l.net



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