linux-kernel - Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

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Message-ID: <20181126200053.GV2113@hirez.programming.kicks-ass.net>
Date:   Mon, 26 Nov 2018 21:00:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>,
        David Laight <David.Laight@...LAB.COM>,
        Borislav Petkov <bp@...en8.de>,
        Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call
 implementation for x86-64

On Mon, Nov 26, 2018 at 11:56:24AM -0600, Josh Poimboeuf wrote:
> Peter suggested updating the text_poke_bp() interface to add a handler
> which is called from int3 context.  This seems to work.

> @@ -760,8 +761,10 @@ int poke_int3_handler(struct pt_regs *regs)
>  	if (user_mode(regs) || regs->ip != (unsigned long)bp_int3_addr)
>  		return 0;
>  
> -	/* set up the specified breakpoint handler */
> -	regs->ip = (unsigned long) bp_int3_handler;
> +	if (bp_int3_handler)
> +		bp_int3_handler(regs);
> +
> +	regs->ip = (unsigned long)bp_int3_resume;
>  
>  	return 1;
>  

Peter also suggested you write that like:

	if (bp_int3_handler)
		bp_int3_handler(regs, resume);
	else
		regs->ip = resume;

That allows 'abusing' @resume as 'data' pointer for @handler. Which
allows for more complicated handlers.