linux-kernel - Re: [PATCH] lib/clz_tab.c: put in lib-y rather than obj-y

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Date:	Tue, 22 Dec 2015 12:46:06 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	cmetcalf@...hip.com
Cc:	linux-kernel@...r.kernel.org, viro@...IV.linux.org.uk,
	jmorris@...ei.org, akpm@...ux-foundation.org,
	sudipm.mukherjee@...il.com
Subject: Re: [PATCH] lib/clz_tab.c: put in lib-y rather than obj-y

From: Chris Metcalf <cmetcalf@...hip.com>
Date: Tue, 22 Dec 2015 12:41:24 -0500

> The clz table (__clz_tab) in lib/clz_tab.c is also provided as part
> of libgcc.a, and many architectures link against libgcc.  To allow
> the linker to avoid a multiple-definition link failure, clz_tab.o
> has to be in lib/lib.a rather than lib/builtin.o.  The specific
> issue is that libgcc.a comes before lib/builtin.o on vmlinux.o's
> link command line, so its _clz.o is pulled to satisfy __clz_tab,
> and then when the remainder of lib/builtin.o is pulled in to satisfy
> all the other dependencies, the __clz_tab symbols conflict.  By
> putting clz_tab.o in lib.a, the linker can simply avoid pulling
> it into vmlinux.o when this situation arises.
> 
> The definitions of __clz_tab are the same in libgcc.a and in the
> kernel; arguably we could also simply rename the kernel version,
> but it's unlikely the libgcc version will ever change to become
> incompatible, so just using it seems reasonably safe.
> 
> Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>

No objections from me:

Acked-by: David S. Miller <davem@...emloft.net>
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