linux-kernel - Re: [RFC PATCH 1/1] x86/kprobes: Use int3 instead of debug trap for single-step

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Date:   Tue, 2 Mar 2021 09:38:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...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>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH 1/1] x86/kprobes: Use int3 instead of debug trap for
 single-step

On Mon, Mar 01, 2021 at 11:08:15PM +0900, Masami Hiramatsu wrote:

> +	default:
> +		if ((opcode & 0xf0) == 0x70) {
> +			/* 1 byte conditional jump */
> +			p->ainsn.emulate_op = kprobe_emulate_jcc;
> +			p->ainsn.jcc.type = opcode & 0xf;
> +			p->ainsn.rel32 = *(char *)insn->immediate.bytes;
> +		}
>  	}

Would it make sense to write that as:

	case 0x70 ... 0x7f:
		/* 1 byte conditional jump */
		p->ainsn.emulate_op = kprobe_emulate_jcc;
		p->ainsn.jcc.type = opcode & 0xf;
		p->ainsn.rel32 = *(char *)insn->immediate.bytes;
		break;

instead? Preferably right before the 0x0f case :-)