linux-kernel - Re: [RESEND][PATCH v3 09/17] x86/static_call: Add out-of-line static call implementation

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Date:   Thu, 26 Mar 2020 15:57:09 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, rostedt@...dmis.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
Subject: Re: [RESEND][PATCH v3 09/17] x86/static_call: Add out-of-line static
 call implementation

On Tue, Mar 24, 2020 at 02:56:12PM +0100, Peter Zijlstra wrote:
> +static void __static_call_transform(void *insn, u8 opcode, void *func)
> +{
> +	const void *code = text_gen_insn(opcode, (long)insn, (long)func);
> +
> +	if (WARN_ONCE(*(u8 *)insn != opcode,
> +		      "unexpected static call insn opcode 0x%x at %pS\n",
> +		      opcode, insn))
> +		return;
> +
> +	if (memcmp(insn, code, CALL_INSN_SIZE) == 0)
> +		return;
> +
> +	text_poke_bp(insn, code, CALL_INSN_SIZE, NULL);

Right, this is working with CALL_INSN_SIZE but ...

> +}
> +
> +void arch_static_call_transform(void *site, void *tramp, void *func)
> +{
> +	mutex_lock(&text_mutex);
> +
> +	if (tramp)
> +		__static_call_transform(tramp, JMP32_INSN_OPCODE, func);

... it gets called with JMP32_INSN_OPCODE too. I mean, both lengths are
equal and all - it is just a bit confusing at a first glance. Maybe slap
a small comment that it is ok.

Thx.

-- 
Regards/Gruss,
    Boris.

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