linux-kernel - Re: [RFC][PATCH 6/7] jump_label: Add a new static

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Date:	Mon, 27 Jul 2015 11:52:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	linux-kernel@...r.kernel.org, mingo@...nel.org
Cc:	jasonbaron0@...il.com, bp@...en8.de, luto@...capital.net,
	tglx@...utronix.de, rostedt@...dmis.org, will.deacon@....com,
	liuj97@...il.com, rabin@....in, ralf@...ux-mips.org,
	ddaney@...iumnetworks.com, benh@...nel.crashing.org,
	michael@...erman.id.au, heiko.carstens@...ibm.com,
	davem@...emloft.net
Subject: Re: [RFC][PATCH 6/7] jump_label: Add a new static_key interface

On Fri, Jul 24, 2015 at 07:52:15PM +0200, Peter Zijlstra wrote:
> --- a/arch/s390/include/asm/jump_label.h
> +++ b/arch/s390/include/asm/jump_label.h
> @@ -12,14 +12,29 @@
>   * We use a brcl 0,2 instruction for jump labels at compile time so it
>   * can be easily distinguished from a hotpatch generated instruction.
>   */
> -static __always_inline bool arch_static_branch(struct static_key *key)
> +static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
>  {
>  	asm_volatile_goto("0:	brcl 0,"__stringify(JUMP_LABEL_NOP_OFFSET)"\n"
>  		".pushsection __jump_table, \"aw\"\n"
>  		".balign 8\n"
>  		".quad 0b, %l[label], %0\n"
>  		".popsection\n"
> -		: : "X" (key) : : label);
> +		: : "X" (&((char *)key)[branch]) : : label);
> +
> +	return false;
> +label:
> +	return true;
> +}
> +
> +static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
> +{
> +	asm_volatile_goto("0:	j %l[l_yes]\n"

Looking at the s390 version of jump_label_make_branch(), this should
have been:

		"brcl 15, %l[l_yes]\n"

I suppose?

> +		".pushsection __jump_table, \"aw\"\n"
> +		".balign 8\n"
> +		".quad 0b, %l[label], %0\n"
> +		".popsection\n"
> +		: : "X" (&((char *)key)[branch]) : : label);
> +
>  	return false;
>  label:
>  	return true;
--
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