linux-kernel - Re: [PATCH] x86/hyperv: Mark hv_ghcb

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Date:   Fri, 10 Mar 2023 07:24:42 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     linux-hyperv@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, decui@...rosoft.com,
        haiyangz@...rosoft.com, kys@...rosoft.com, wei.liu@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        thomas.lendacky@....com, peterz@...radead.org,
        kernel-dev@...lia.com, kernel@...ccoli.net,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] x86/hyperv: Mark hv_ghcb_terminate() as noreturn

On Fri, Mar 10, 2023 at 11:02:52AM -0300, Guilherme G. Piccoli wrote:
> Hey folks, after getting the warning myself a quick search led me to Arnd's
> thorough report - investigating a bit, this seems to be the proper solution.
> 
> Notice I didn't add the function to objtool's static list, seems this is
> unnecessary in this case - lemme know otherwise!
> Thanks in advance for reviews,

I'd recommend also adding it to the objtool global_noreturns list,
otherwise this patch will probably trigger warnings with other non-IBT
configs, in cases where the function is called from another translation
unit, where GCC knows the function is noreturn but objtool doesn't.

We're looking at ways of eliminating global_noreturns, but it's
unfortunately still a necessary evil at this point.

Also, FWIW, I have a change coming soon which make these warnings much
easier to diagnose.

-- 
Josh