linux-kernel - Re: Remaining randconfig objtool warnings, linux-next-20200428

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Date:   Fri, 1 May 2020 12:50:22 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Remaining randconfig objtool warnings, linux-next-20200428

On Fri, May 01, 2020 at 07:26:16PM +0200, Peter Zijlstra wrote:
> On Fri, May 01, 2020 at 07:21:31PM +0200, Arnd Bergmann wrote:
> > On Thu, Apr 30, 2020 at 4:05 PM Arnd Bergmann <arnd@...db.de> wrote:
> > it gets into undefined behavior and stops emitting code after the call to
> 
> > Do we consider this expected behavior on gcc's side, or is it something
> > that should not happen and needs a gcc bug report?
> 
> When it hits UB it is of course free to do whatever it damn well
> pleases, but just stopping code gen seems a little extreme, at least
> issue a WARN that something is up or so.
> 
> Not sure how the GCC folks feel about this though.

When we've seen truncated code flow like this in the past, it's either
been a code bug (undefined behavior) or a GCC bug.  So this is new.

Is it only seen with GCC_PLUGIN_SANCOV enabled?  Maybe (hopefully) it's
an issue with the plugin and how it interacts with GCC 10.

-- 
Josh