linux-kernel - Re: linux-next: Tree for Mar 18 (objtool)

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Message-ID: <20200318182352.2dgwwl4ugbwndi4x@treble>
Date:   Wed, 18 Mar 2020 13:23:52 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: linux-next: Tree for Mar 18 (objtool)

On Wed, Mar 18, 2020 at 09:48:01AM -0700, Randy Dunlap wrote:
> On 3/18/20 4:09 AM, Stephen Rothwell wrote:
> > Hi all,
> > 
> > Changes since 20200317:
> > 
> 
> Hi,
> 
> For some reason, the attached .config file generates over 350 objtool warnings.
> There are all "unreachable instruction" warnings.
> 
> Here is a small sample:
> 
> mm/page-writeback.o: warning: objtool: __set_page_dirty_nobuffers()+0x25b: unreachable instruction
> kernel/sched/fair.o: warning: objtool: load_balance()+0x54c: unreachable instruction
> kernel/power/process.o: warning: objtool: freeze_kernel_threads()+0x115: unreachable instruction
> mm/readahead.o: warning: objtool: read_cache_pages_invalidate_page()+0x1b5: unreachable instruction
> kernel/power/suspend.o: warning: objtool: suspend_devices_and_enter()+0x101f: unreachable instruction
> kernel/sched/rt.o: warning: objtool: dequeue_top_rt_rq()+0x67: unreachable instruction

This seems to be caused by 

  545ed6816b72 ("ubsan: add trap instrumentation option")

Kees, any idea why that commit causes at least some BUG() statements to
output an extra UD2?

-- 
Josh