linux-kernel - Re: compile x86

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Date:	Wed, 24 Jul 2013 23:05:12 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	Jianpeng Ma <majianpeng@...il.com>, Tom Rini <trini@...com>,
	Rusty Russell <rusty@...tcorp.com.au>
Cc:	tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: compile x86_64 waring

[Added Tom and Rusty because they might be able to say what's really
going on here.]

On Fri, 2013-07-05 at 19:56 +0800, majianpeng wrote:
> Compile x86_64 meet those messages:
> WARNING: arch/x86/mm/built-in.o(.text.unlikely+0xbf8): Section mismatch in reference from the function __node_set.constprop.0() to the variable .init.data:numa_nodes_parsed
> The function __node_set.constprop.0() references
> the variable __initdata numa_nodes_parsed.
> This is often because __node_set.constprop.0 lacks a __initdata 
> annotation or the annotation of numa_nodes_parsed is wrong.
> 
> WARNING: arch/x86/built-in.o(.text.unlikely+0x171d): Section mismatch in reference from the function __node_set.constprop.0() to the variable .init.data:numa_nodes_parsed
> The function __node_set.constprop.0() references
> the variable __initdata numa_nodes_parsed.
> This is often because __node_set.constprop.0 lacks a __initdata 
> annotation or the annotation of numa_nodes_parsed is wrong.

0) I noticed these too, on v3.11-rc1 and v3.12.-rc2. I assume Jianpeng
Ma reported these for a linux-next release that preceded v3.11-rc1.

1) The only hits for node_set and numa_nodes_parsed in arch/x86/mm are
in amdtopology.c, numa.c, and srat.c. If I peek at the object files
generated for these three files I notice that numa.o and srat.o have
node_set() in their .text.unlikely section. (amdtopology.o doesn't have
a .text.unlikely section.) 

2) I guess that since commit 06df44ee41442d83be061c5fd1b1de4f5fc6fbbf
("modpost.c: Add .text.unlikely to TEXT_SECTIONS"), which was included
in v3.11-rc1, code in .text.unlikely sections generates a mismatch
warning if it references __initdata code (and numa_nodes_parsed is
__initdata). But all calls of node_set() in these two files are from
within functions that are marked __init. And I think references from
__init code to __initdata code shouldn't lead to mismatch warnings,
should they?

3) So this looks like a false positive to me (but I'm not at all
familiar with, well, the section mismatch checks). Would there be a way
to silence this warning? Other than dropping __initdata from
numa_nodes_parsed, of course.

Paul Bolle

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