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Re: current binutils trunk fails to build bootable kernel image for some configurations
- From: Alan Modra <amodra at bigpond dot net dot au>
- To: Matthias Klose <doko at ubuntu dot com>
- Cc: binutils <binutils at sourceware dot org>, Bastian Blank <waldi at debian dot org>, Linus Torvalds <torvalds at linux-foundation dot org>, linux-kernel at vger dot kernel dot org, Kiko Piris <kernel at pirispons dot net>, Damien Wyart <damien dot wyart at free dot fr>, Greg KH <gregkh at suse dot de>, Wolfgang Walter <wolfgang dot walter at stwm dot de>
- Date: Thu, 23 Jul 2009 10:19:39 +0930
- Subject: Re: current binutils trunk fails to build bootable kernel image for some configurations
- References: <4A6746B9.9010603@ubuntu.com>
On Wed, Jul 22, 2009 at 01:04:57PM -0400, Matthias Klose wrote:
> this was reported as http://bugs.debian.org/537389, I currently don't
> have much more information, besides that one of the Debian kernel
> maintainers did identify
>
> 2009-07-11 Alan Modra <amodra@bigpond.net.au>
>
> * ldlang.c (insert_os_after): Don't tie assignments to non-alloc
> output sections.
>
> this patch as the one causing the wrongly built kernel. However I don't
> see this checkin mentioned on the ML.
The discussion happened on bug-binutils.
http://lists.gnu.org/archive/html/bug-binutils/2009-07/msg00067.html
> Bastian Blank did check that the
> problem goes away with a binutils build from trunk and this patch
> reverted. Some more analysis in http://lkml.org/lkml/2009/7/21/400
The biggest problem is that the kernel linker script doesn't mention
all sections, which means ld must choose a place for the unmentioned
sections (orphans). Sometimes ld's placement isn't how a naive
programmer would expect.
In this case:
. = ALIGN(PAGE_SIZE);
.data_nosave : AT(ADDR(.data_nosave) - LOAD_OFFSET) {
ld stuck an orphan section between the two statements. Which meant
that the start of .data_nosave is not aligned (and since the end is
aligned by following statements, it means that .data_nosave also has
padding inserted). It would be more robust to write:
.data_nosave ALIGN(PAGE_SIZE) : AT(ADDR(.data_nosave) - LOAD_OFFSET) {
--
Alan Modra
Australia Development Lab, IBM