linux-kernel - Re: [PATCH 55/74] lto, workaround: Add workaround for initcall reordering

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Message-ID: <20120819150140.GP11413@one.firstfloor.org>
Date:	Sun, 19 Aug 2012 17:01:40 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jan Beulich <jbeulich@...e.com>
Cc:	andi@...stfloor.org, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	akpm@...ux-foundation.org, mmarek@...e.cz,
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 55/74] lto, workaround: Add workaround for initcall reordering

On Sun, Aug 19, 2012 at 09:46:04AM +0100, Jan Beulich wrote:
> >>> Andi Kleen <andi@...stfloor.org> 08/19/12 5:05 AM >>>
> >Work around a LTO gcc problem: when there is no reference to a variable
> >in a module it will be moved to the end of the program. This causes
> >reordering of initcalls which the kernel does not like.
> >Add a dummy reference function to avoid this. The function is
> >deleted by the linker.
> 
> This is not even true on x86, not to speak of generally.

Why is it not true ? 

__initcall is only defined for !MODULE and there __exit discards.

> 
> >+#ifdef CONFIG_LTO
> >+/* Work around a LTO gcc problem: when there is no reference to a variable
> >+ * in a module it will be moved to the end of the program. This causes
> >+ * reordering of initcalls which the kernel does not like.
> >+ * Add a dummy reference function to avoid this. The function is 
> >+ * deleted by the linker.
> >+ */
> >+#define LTO_REFERENCE_INITCALL(x) \
> >+    ; /* yes this is needed */            \
> >+    static __used __exit void *reference_##x(void)     \
> 
> Why not put it into e.g. section .discard.text? That could be expected to be
> discarded by the linker without being arch dependent, as long as all arches
> use DISCARDS in their linker script.


That's what __exit does, doesn't it?

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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