linux-kernel - Re: [tip:core/urgent] objtool: Fix __unreachable section relocation size

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Date:   Wed, 01 Mar 2017 00:15:38 -0800
From:   hpa@...or.com
To:     linux-tip-commits@...r.kernel.org,
        tip-bot for Josh Poimboeuf <tipbot@...or.com>
CC:     a.p.zijlstra@...llo.nl, torvalds@...ux-foundation.org,
        jpoimboe@...hat.com, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...nel.org
Subject: Re: [tip:core/urgent] objtool: Fix __unreachable section relocation size

On March 1, 2017 12:10:59 AM PST, tip-bot for Josh Poimboeuf <tipbot@...or.com> wrote:
>Commit-ID:  90a7e63a31b8f7d630d12ef0d8d37d3ab87f76e5
>Gitweb:    
>http://git.kernel.org/tip/90a7e63a31b8f7d630d12ef0d8d37d3ab87f76e5
>Author:     Josh Poimboeuf <jpoimboe@...hat.com>
>AuthorDate: Wed, 1 Mar 2017 00:05:04 -0600
>Committer:  Ingo Molnar <mingo@...nel.org>
>CommitDate: Wed, 1 Mar 2017 07:38:25 +0100
>
>objtool: Fix __unreachable section relocation size
>
>Linus reported the following commit broke module loading on his laptop:
>
>d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead
>ends")
>
>It showed errors like the following:
>
>  module: overflow in relocation type 10 val ffffffffc02afc81
>  module: 'nvme' likely not compiled with -mcmodel=kernel
>
>The problem is that the __unreachable section addresses are stored
>using
>the '.long' asm directive, which isn't big enough for .text section
>relative kernel addresses.  Use '.quad' instead.
>
>Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
>Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
>Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
>Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>Cc: Peter Zijlstra <peterz@...radead.org>
>Cc: Thomas Gleixner <tglx@...utronix.de>
>Fixes: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other
>dead ends")
>Link: http://lkml.kernel.org/r/20170301060504.oltm3iws6fmubnom@treble
>Signed-off-by: Ingo Molnar <mingo@...nel.org>
>---
> include/linux/compiler-gcc.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/include/linux/compiler-gcc.h
>b/include/linux/compiler-gcc.h
>index 76e28c2..91a77a5 100644
>--- a/include/linux/compiler-gcc.h
>+++ b/include/linux/compiler-gcc.h
>@@ -201,7 +201,7 @@
> #define annotate_unreachable() ({					\
> 	asm("%c0:\t\n"							\
> 	    ".pushsection __unreachable, \"a\"\t\n"			\
>-	    ".long %c0b\t\n"						\
>+	    ".quad %c0b\t\n"						\
> 	    ".popsection\t\n" : : "i" (__LINE__));			\
> })
> #else

Or perhaps better use relative addresses, so:

.long foo - (.+4)


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