linux-kernel - Re: Why do kprobes and uprobes singlestep?

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Message-ID: <YDd1HTDv/Yg3ZX6p@hirez.programming.kicks-ass.net>
Date:   Thu, 25 Feb 2021 10:59:57 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>, X86 ML <x86@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: Why do kprobes and uprobes singlestep?

On Wed, Feb 24, 2021 at 11:45:10AM -0800, Andy Lutomirski wrote:
> I guess I see the point for CALL, JMP and RET, but it seems like we
> could emulate those cases instead fairly easily.

Today, yes. CALL emulation was 'recently' made possible by having #BP
have a stack gap. We have emulation for all 3 those instructions
implemented in asm/text-patching.h, see int3_emulate_$insn().