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

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Message-ID: <20170301124300.7upqx3aefcqj46ky@treble>
Date:   Wed, 1 Mar 2017 06:43:00 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        a.p.zijlstra@...llo.nl, torvalds@...ux-foundation.org,
        peterz@...radead.org, hpa@...or.com,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/urgent] objtool: Fix __unreachable section relocation
 size

On Wed, Mar 01, 2017 at 11:37:12AM +0100, Ingo Molnar wrote:
> 
> * 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
> 
> BTW., beyond inadequate testing, another mistake I failed to notice during review 
> is that the title of the patch was actively misleading: an "objtool: " prefix 
> suggests a change that only affects objtool, while the changes here were to 
> compiler-gcc.h, affecting pretty much everyone...
> 
> So a better, more informative commit title would have been:
> 
>    objtool, compiler.h: Improve detection of BUG() and other dead ends
> 
> ... to at least warn people about the wider impact. (To be honest I personally 
> probably would still not have noticed the bug, but maybe others.)
> 
> Along the same lines I'll fix the title of this fix patch as well, once a final 
> version has been reached.

Yeah, that would have been a more informative title indeed.

For what seemed (to me) like a straightforward improvement, which was
90% objtool and 10% kernel, that commit introduced a surprising number
of subtle bugs in the kernel.

-- 
Josh