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

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Date:	Thu, 17 Feb 2011 09:45:37 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dmitry Torokhov <dtor@...are.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Linux/m68k" <linux-m68k@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 1/3] module: deal with alignment issues in built-in module versions

On Thu, Feb 17, 2011 at 9:31 AM, Dmitry Torokhov <dtor@...are.com> wrote:
>
> From what I understand __attribute__ ((aligned(x))) only guarantees
> minimum alignment, not exact (gapless) alignment. GCC seems to lay out
> pointers in the section without gaps on all arches that we have.

I still don't see the problem.

Have you actually _tried_ just adding the proper alignment to before
the __modver thing in include/asm-generic/vmlinux.lds.h ?

As far as I can tell, the bug is really simple:
 - the section is not aligned
 - but we told the compiler that that structure is aligned

End result: there is a gap between the section start and the first structure.

And the fix seems obvious: just make sure that the section is
sufficiently aligned.

IOW, why isn't the proper fix the obvious trivial one (attached)?

                                    Linus

View attachment "patch.diff" of type "text/x-patch" (744 bytes)