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

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Date:   Fri, 10 Jul 2020 19:08:25 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.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, 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?

-- Steve


> -		return;
> +	switch (type) {
> +	case CALL:
> +		code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
> +		break;
> +
> +	case NOP:
> +		code = ideal_nops[NOP_ATOMIC5];
> +		break;
> +
> +	case JMP:
> +		code = text_gen_insn(JMP32_INSN_OPCODE, insn, func);
> +		break;
> +
> +	case RET:
> +		code = text_gen_insn(RET_INSN_OPCODE, insn, func);
> +		size = RET_INSN_SIZE;
> +		break;
> +	}
>  
> -	if (memcmp(insn, code, CALL_INSN_SIZE) == 0)
> +	if (memcmp(insn, code, size) == 0)
>  		return;
>  
> -	text_poke_bp(insn, code, CALL_INSN_SIZE, NULL);
> +	text_poke_bp(insn, code, size, NULL);
>  }
>