linux-kernel - Re: [PATCH 2/4] objtool: Implement jump_assert for _static_cpu

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Message-ID: <20180115191541.zui3ko5avbwfvo2f@pd.tnic>
Date:   Mon, 15 Jan 2018 20:15:41 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        David Woodhouse <dwmw2@...radead.org>,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>
Subject: Re: [PATCH 2/4] objtool: Implement jump_assert for _static_cpu_has()

On Mon, Jan 15, 2018 at 01:11:51PM -0600, Josh Poimboeuf wrote:
> Well, to clarify, it would solve _some_ of the problem.  Maybe even most
> of the problem.  We'd still need to special-case jump labels in objtool
> (like in 1/4), but that's probably not a big deal.
> 
> So, contradicting my previous answer here... yes, it would help.

Yeah, so PeterZ was asking on IRC today how to detect static_cpu_has()
and even if we do some magic matching, nothing beats an explicit flag.

And I'm proposing this because the flags thing has come up in the past
already. So it's not like it won't find more users. We can do all kinds
of fancy alternatives processing when we tag the call sites properly.
:-)

Now lemme look at the rest of the patchset.

-- 
Regards/Gruss,
    Boris.

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