Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 28 Jun 2018 10:50:03 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        x86@kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 2/5] kernel/jump_label: implement generic support for
 relative references
Message-ID: <20180628085003.GA2494@hirez.programming.kicks-ass.net>
References: <20180627160604.8154-1-ard.biesheuvel@linaro.org>
 <20180627160604.8154-3-ard.biesheuvel@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180627160604.8154-3-ard.biesheuvel@linaro.org>
User-Agent: Mutt/1.10.0 (2018-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Jun 27, 2018 at 06:06:01PM +0200, Ard Biesheuvel wrote:
> diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
> index 86ec0652d3b1..aa203dffe72c 100644
> --- a/include/linux/jump_label.h
> +++ b/include/linux/jump_label.h
> @@ -121,6 +121,32 @@ struct static_key {
>  #include <asm/jump_label.h>
>  
>  #ifndef __ASSEMBLY__
> +#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
> +
> +struct jump_entry {
> +	int code;
> +	int target;
> +	int key;
> +};

I much prefer you use 'u32' there.


> +static void jump_label_swap(void *a, void *b, int size)
> +{
> +	long delta = (unsigned long)a - (unsigned long)b;
> +	struct jump_entry *jea = a;
> +	struct jump_entry *jeb = b;
> +	struct jump_entry tmp = *jea;
> +
> +	jea->code	= jeb->code - delta;
> +	jea->target	= jeb->target - delta;
> +	jea->key	= jeb->key - delta;
> +
> +	jeb->code	= tmp.code + delta;
> +	jeb->target	= tmp.target + delta;
> +	jeb->key	= tmp.key + delta;
> +}
> +
>  static void
>  jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
>  {
> @@ -56,7 +72,9 @@ jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
>  
>  	size = (((unsigned long)stop - (unsigned long)start)
>  					/ sizeof(struct jump_entry));
> -	sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
> +	sort(start, size, sizeof(struct jump_entry), jump_label_cmp,
> +	     IS_ENABLED(CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE) ? jump_label_swap
> +							      : NULL);
>  }

That will result in jump_label_swap being an unused symbol for some
compile options.

Would it not be much nicer to write that like:

static void jump_label_swap(void *a, void *b, int size)
{
	struct jump_entry *jea = a, *jeb = b;

#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
	long delta = a - b;

	jea->code += delta;
	jea->target += delta;
	jea->key += delta;

	jeb->code -= delta;
	jeb->target -= delta;
	jeb->key -= delta;
#else

	swap(*jea, *jeb);
}

And then unconditionally use jump_label_swap().