Re: [PATCH 1/3] module: deal with alignment issues in built-in module versions

Dmitry Torokhov
2011-02-22T07:02:40Z

On Mon, Feb 21, 2011 at 06:03:16PM -0800, Linus Torvalds wrote:
> On Mon, Feb 21, 2011 at 5:58 PM, Benjamin Herrenschmidt
> <benh@kernel.crashing.org> wrote:
> >
> > The only sane thing I can see is make sure that such structures that
> > we put into sections "arrays" like that are naturally aligned with
> > padding.
>
> The sad part is, that assuming I read the gcc sources correctly (see
> the earlier emails where David pointed to it), that alignment is:
> - architecture-specific
> - depends on the size of the structure
> - seems to depend on the version of gcc itself.
>
> The _one_ safe case is likely to be "structure size is a power of
> two". And it does look like using a pointer is going to be safe, not
> only because the gcc auto-alignment only triggers for things like
> structs/unions/arrays, but because at least the x86 code only does it
> if the structure was bigger than the alignment size itself.
>
> So using pointer indirection is likely to be safe. It's still ugly and
> annoying as heck, though.
>

Regardless the approach we'll take I think the following patch is also
needed (for cris architecture). I am not sure why __param section is
inly defined for one specific subarch but I they need __param they'll
need __modev as well.

Thanks,

Dmitry

>From a567280f900c15891a55e7ea4e2919b38e1d1a01 Mon Sep 17 00:00:00 2001
From: Dmitry Torokhov <dtor@vmware.com>
Date: Thu, 17 Feb 2011 13:12:26 -0800
Subject: [PATCH] cris: add missing __modver section

Commit e94965ed5beb23c6fabf7ed31f625e66d7ff28de added a new __modver
section to store module version information for drivers built into the
kernel, but missed the fact that cris does some additional steps to
set up sections.

Signed-off-by: Dmitry Torokhov <dtor@vmware.com>
---
arch/cris/kernel/vmlinux.lds.S | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/arch/cris/kernel/vmlinux.lds.S b/arch/cris/kernel/vmlinux.lds.S
index 4422189..fae1b7b 100644
--- a/arch/cris/kernel/vmlinux.lds.S
+++ b/arch/cris/kernel/vmlinux.lds.S
@@ -73,6 +73,10 @@ SECTIONS
.init.data : { INIT_DATA }
.init.setup : { INIT_SETUP(16) }
#ifdef CONFIG_ETRAX_ARCH_V32
+ __start___modver = .;
+ __modver : { *(__modver) }
+ __stop___modver = .;
+
__start___param = .;
__param : { *(__param) }
__stop___param = .;
--
1.7.3.2