linux-kernel - Re: [PATCH] x86: pad assembly functions with INT3

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Message-ID: <E67F8616-B5D4-47E5-9017-A1B127C103EA@zytor.com>
Date:   Mon, 14 May 2018 23:59:32 -0700
From:   hpa@...or.com
To:     Ingo Molnar <mingo@...nel.org>
CC:     David Laight <David.Laight@...LAB.COM>,
        "'Alexey Dobriyan'" <adobriyan@...il.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86: pad assembly functions with INT3

On May 14, 2018 11:54:05 PM PDT, Ingo Molnar <mingo@...nel.org> wrote:
>
>* hpa@...or.com <hpa@...or.com> wrote:
>
>> > I guess it won't try to speculatively execute the 'pad'
>instructions - but you 
>> > can never really tell!
>> >
>> >	David
>> 
>> The CPU doesn't speculate down past an unconditional control
>transfer. Doing so 
>> would be idiotic.
>
>I think, when it comes to speculative execution, our general
>expectation that CPUs 
>don't do idiotic things got somewhat weakened in the past year or so
>...
>
>Thanks,
>
>	Ingo

Sort-of-kind-of... the things that have cropped up were reasonable consequences of designing under a set of assumptions which turned out to be incorrect. Speculating through an unconditional control transfer did not make sense under those assumptions either.
-- 
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