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SubjectRe: [tip:x86/urgent] x86: Add back _end symbol that is missing from Symbol.map
On Sun, Nov 08, 2009 at 12:48:29PM +0100, Ingo Molnar wrote:
>
> * Sam Ravnborg <sam@ravnborg.org> wrote:
>
> > On Sun, Nov 08, 2009 at 11:07:12AM +0000, tip-bot for Hannes Reinecke wrote:
> > > Commit-ID: d1e4d37b79e944f6351ae38eb1ca7c9f7b506e76
> > > Gitweb: http://git.kernel.org/tip/d1e4d37b79e944f6351ae38eb1ca7c9f7b506e76
> > > Author: Hannes Reinecke <hare@suse.de>
> > > AuthorDate: Wed, 4 Nov 2009 07:19:32 -0800
> > > Committer: Ingo Molnar <mingo@elte.hu>
> > > CommitDate: Sun, 8 Nov 2009 12:05:03 +0100
> > >
> > > x86: Add back _end symbol that is missing from Symbol.map
> > >
> > > With 2.6.31 'crash' on x86_64 falls flat on its face as the
> > > '_end' symbol is missing from the System.map file.
> > >
> > > The culprit is commit 091e52c3551d3031343df24b573b770b4c6c72b6,
> > > which moved the '_end' symbol into it's own section. Apparently
> > > this causes kallsyms to not reference it properly.
> > >
> > > So do not include _end in it's own section.
> > >
> > > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > > Cc: Sam Ravnborg <sam@ravnborg.org>
> > > Cc: <stable@kernel.org> # .31.x
> > > LKML-Reference: <200911041519.nA4FJWEW030164@imap1.linux-foundation.org>
> > > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> >
> > I'm afraid this will break a RELOCTABLE i386 kernel.
> >
> > We fixed this up some time ago where we had to
> > move the symbol definition inside a section
> > to prevent the symbol being absolute.
>
> ah, indeed. So ... the question is then, why did _end disappear from
> System.map?
I think ld discards zero size sections. No need to keep them around
if they are empty.

Following patch should fix it up in a better way.
I reused most of Hannes changelog.

Sam

[PATCH] x86: Add back _end symbol that is missing from Symbol.map

With 2.6.31 'crash' on x86_64 falls flat on its face as the
'_end' symbol is missing from the System.map file.

The culprit is commit 091e52c3551d3031343df24b573b770b4c6c72b6,
which moved the '_end' symbol into it's own section.

The problem is likely that ld discards empty sections.
So move the definition of _end into the last section defined.

Cc: Hannes Reinecke <hare@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@kernel.org> # .31.x
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>


diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 92929fb..c58a6e3 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -289,9 +289,12 @@ SECTIONS
. += 64 * 1024; /* 64k alignment slop space */
*(.brk_reservation) /* areas brk users have reserved */
__brk_limit = .;
- }

- .end : AT(ADDR(.end) - LOAD_OFFSET) {
+ /*
+ * To support RELOCTABLE kernel _end must be inside a section.
+ * And ld is know to discard empty section so we locate _end in
+ * last section we define.
+ */
_end = .;
}


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