linux-kernel - Re: [PATCH v6 13/17] static_call: Add static_call

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Date:   Sat, 11 Jul 2020 07:09:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com,
        pbonzini@...hat.com, mathieu.desnoyers@...icios.com,
        linux@...musvillemoes.dk
Subject: Re: [PATCH v6 13/17] static_call: Add static_call_cond()

On Fri, Jul 10, 2020 at 07:08:25PM -0400, Steven Rostedt wrote:
> On Fri, 10 Jul 2020 15:38:44 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > +static void __static_call_transform(void *insn, enum insn_type type, void *func)
> >  {
> > -	const void *code = text_gen_insn(opcode, insn, func);
> > +	int size = CALL_INSN_SIZE;
> > +	const void *code;
> >  
> > -	if (WARN_ONCE(*(u8 *)insn != opcode,
> > -		      "unexpected static call insn opcode 0x%x at %pS\n",
> > -		      opcode, insn))
> 
> I would still feel better if we did some sort of sanity check before
> just writing to the text. Confirm this is a jmp, call, ret or nop?

I'll see if I can come up with something, but I'm not sure we keep
enough state to be able to reconstruct what should be there.