linux-kernel - Re: missing .data.shared_align placement in vmlinux

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Message-ID: <20100804115658.GA21357@merkur.ravnborg.org>
Date:	Wed, 4 Aug 2010 13:56:58 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Alan Jenkins <alan-jenkins@...fmail.co.uk>
Subject: Re: missing .data.shared_align placement in vmlinux

On Fri, May 21, 2010 at 04:58:53PM -0400, Mike Frysinger wrote:
> am i missing something or does the .data.shared_align section lack
> definition in vmlinux.lds.h and all arch vmlinux.lds.S files ?
> 
> with the recent change "net: remove time limit in process_backlog()",
> the softnet_data variable changed from "DEFINE_PER_CPU()" to
> "DEFINE_PER_CPU_ALIGNED()" which moved it from the .data section to
> the .data.shared_align section.  i'm not saying this patch is wrong,
> just that is what caused me to notice this larger problem.  no one
> else in the kernel is using this aligned macro variant, so i imagine
> that's why no one has noticed yet.
> 
> since .data.shared_align isnt declared in any vmlinux files that i can
> see, the linker just places it last.  this "just works" for most
> people, but when building a ROM kernel on Blackfin systems, it causes
> section overlap errors:
> bfin-uclinux-ld.real: section .init.data [00000000202e06b8 ->
> 00000000202e48b7] overlaps section .data.shared_aligned
> [00000000202e06b8 -> 00000000202e0723]
> i imagine other arches which support the ROM config option and thus do
> funky placement would see similar issues ...
> 
> on x86, it is stuck in a dedicated section:
>   [ 8] .data             PROGBITS        ffffffff810ec000 2ec000
> 0303a8 00  WA  0   0 4096
>   [ 9] .data.shared_alig PROGBITS        ffffffff8111c3c0 31c3c0
> 0000c8 00  WA  0   0 64
> 
> the ifdef forest in asm-generic/percpu.h is beyond a quick glance &
> fix, so i leave it up to someone else ;)

as there any resolution on this?
I briefly looked at it some time ago.
And it looks like a plain oversight.

But I was also a bit lost in the forest of ifdef land...

	Sam
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