linux-kernel - Re: [RFC PATCH 03/14] arm: kprobes: Use generic kretprobe trampoline handler

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Date:   Wed, 26 Aug 2020 16:10:25 +0200
From:   peterz@...radead.org
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Eddy Wu <Eddy_Wu@...ndmicro.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, "David S . Miller" <davem@...emloft.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH 03/14] arm: kprobes: Use generic kretprobe trampoline
 handler

On Wed, Aug 26, 2020 at 04:08:52PM +0200, peterz@...radead.org wrote:
> On Wed, Aug 26, 2020 at 10:46:43PM +0900, Masami Hiramatsu wrote:
> >  static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
> >  {
> > +	return (void *)kretprobe_trampoline_handler(regs,
> > +				(unsigned long)&kretprobe_trampoline,
> > +				regs->ARM_fp);
> >  }
> 
> Does it make sense to have the generic code have a weak
> trampoline_handler() implemented like the above? It looks like a number
> of architectures have this trivial variant and it seems pointless to
> duplicate this.

Argh, I replied to the wrong variant, I mean the one that uses
kernel_stack_pointer(regs).

Then the architecture only needs to implement kernel_stack_pointer() if
there is nothing else to do.