linux-kernel - Re: [PATCH] parisc: fix module loading failure of large kernel modules (take 4)

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Date:	Wed, 31 Dec 2008 18:39:55 +0100
From:	Helge Deller <deller@....de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>
CC:	linux-parisc <linux-parisc@...r.kernel.org>,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Kyle McMartin <kyle@...artin.ca>,
	Randolph Chung <randolph@...sq.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>,
	John David Anglin <dave@...uly1.hia.nrc.ca>
Subject: Re: [PATCH] parisc: fix module loading failure of large kernel modules
 (take 4)

Linus Torvalds wrote:
> 
> On Wed, 31 Dec 2008, Helge Deller wrote:
>> [PATCH 1/2] module.c: fix module loading failure of large kernel modules
>>
>> When creating the final layout of a kernel module in memory, allow the
>> module loader to reserve some additional memory in front of a given section.
>> This is currently only needed for the parisc port which needs to put the
>> stub entries there to fulfill the 17/22bit PCREL relocations with large
>> kernel modules like xfs.
>>
>> Differences of this patch to previous versions:
>> - added weak funtion arch_module_section_size()
> 
> This doesn't work.
> 
> We've had this bug several times now, and one of them just very recently.
> 
> Some gcc versions will inline weak functions if they are in scope - even 
> if there is a non-weak function somewhere else. So you MUST NOT have the 
> weak definition in the same file (or indirectly called through some inline 
> functions in a header file) as the call. Because if you do, then any user 
> with the wrong version of gcc will get the weak function semantics, even 
> if it was meant to be overridden by something else.

Ok, that might explain why I saw some strange things in the unwind tables
after that I switched to using the weak function (hppa-crosscompiler, gcc-3.3.4).

>> +/* Additional bytes needed by arch in front of individual sections */
>> +unsigned int __attribute__ ((weak)) arch_module_section_size(
>> +		struct module *mod, unsigned int section)
> 
> We don't write out that whole "__attribute__" crud. We use
> 
> 	unsigned in __weak arch_module_section_size(struct module *mod, unsigned int section)
> 
> instead.

Ok.

> But as mentioned, it needs to be in another compilation unit.

Understood.

Rusty, back to you for an advise on how to continue ;-)
(I assume Rusty is just right now celebrating new-year)

Helge
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