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

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Message-ID: <20fb84fd5eef4c45b2d38d0290235d5d@AcuMS.aculab.com>
Date:   Thu, 10 May 2018 16:39:55 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alexey Dobriyan' <adobriyan@...il.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>
CC:     "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

From: Alexey Dobriyan
> Sent: 07 May 2018 22:38
> 
> Use INT3 instead of NOP. All that padding between functions is
> an illegal area, no legitimate code should jump into it.
> 
> I've checked x86_64 allyesconfig disassembly, all changes looks sane:
> INT3 is only used after RET or unconditional JMP.

I thought there was a performance penalty (on at least some cpu)
depending on the number of and the actual instructions used for padding.

I believe that is why gcc generates a small number of very long 'nop'
instructions when padding code.

	David