linux-kernel - Re: [PATCH 3/3 v5] livepatch: Use the default ftrace_ops instead of REGS when ARGS is available

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Message-ID: <20201112082144.GS2628@hirez.programming.kicks-ass.net>
Date:   Thu, 12 Nov 2020 09:21:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>, live-patching@...r.kernel.org
Subject: Re: [PATCH 3/3 v5] livepatch: Use the default ftrace_ops instead of
 REGS when ARGS is available

On Wed, Nov 11, 2020 at 08:15:19PM -0500, Steven Rostedt wrote:

> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index e00fe88146e0..235385a38bd9 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -54,6 +54,9 @@ arch_ftrace_get_regs(struct ftrace_regs *fregs)
>  		return NULL;
>  	return &fregs->regs;
>  }
> +
> +#define ftrace_regs_set_ip(fregs, _ip)		\
> +	do { (fregs)->regs.ip = (_ip); } while (0)
>  #endif
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE
> diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
> index 1fde1ab6559e..59a08d5c6f1d 100644
> --- a/arch/x86/include/asm/livepatch.h
> +++ b/arch/x86/include/asm/livepatch.h
> @@ -12,9 +12,9 @@
>  #include <asm/setup.h>
>  #include <linux/ftrace.h>
>  
> -static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
>  {
> -	regs->ip = ip;
> +	ftrace_regs_set_ip(fregs, ip);
>  }
>  

The normal variant is called instruction_pointer_set(), should this be
called ftrace_instruction_pointer_set() ?

(and yes, I hate the long name too).

Also, do you want something like:

unsigned long ftrace_regs_get_register(struct ftrace_regs *regs, unsigned int offset)
{
	switch (offset / sizeof(long)) {
	case  4: /* RBP */

	case  8: /* R9  */
	case  9: /* R8  */
	case 10: /* RAX */
	case 11: /* RCX */
	case 12: /* RDX */
	case 13: /* RSI */
	case 14: /* RDI */
	case 15: /* ORIG_RAX */
	case 16: /* RIP */
		return *(unsigned long *)regs->regs + offset;

	default:
		WARN_ON_ONCE(1);
	}
	return 0;
}