Re: [RFC][PATCH 6/7] jump_label: Add a new static_key interface

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jul 24, 2015 at 07:52:15PM +0200, Peter Zijlstra wrote:
> --- a/arch/sparc/include/asm/jump_label.h
> +++ b/arch/sparc/include/asm/jump_label.h
> @@ -7,16 +7,32 @@
>  
>  #define JUMP_LABEL_NOP_SIZE 4
>  
> -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("1:\n\t"
> -			 "nop\n\t"
> -			 "nop\n\t"

It just occurred to me that this second nop is a branch delay slot, and
therefore..

> -			 ".pushsection __jump_table,  \"aw\"\n\t"
> -			 ".align 4\n\t"
> -			 ".word 1b, %l[l_yes], %c0\n\t"
> -			 ".popsection \n\t"
> -			 : :  "i" (key) : : l_yes);
> +	asm_volatile_goto("1:\n\t"
> +		 "nop\n\t"
> +		 "nop\n\t"
> +		 ".pushsection __jump_table,  \"aw\"\n\t"
> +		 ".align 4\n\t"
> +		 ".word 1b, %l[l_yes], %c0\n\t"
> +		 ".popsection \n\t"
> +		 : :  "i" (&((char *)key)[branch]) : : l_yes);
> +
> +	return false;
> +l_yes:
> +	return true;
> +}
> +
> +static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
> +{
> +	asm_volatile_goto("1:\n\t"
> +		 "b %l[l_yes]\n\t"

should very much be here too:

		"nop\n\t"

> +		 ".pushsection __jump_table,  \"aw\"\n\t"
> +		 ".align 4\n\t"
> +		 ".word 1b, %l[l_yes], %c0\n\t"
> +		 ".popsection \n\t"
> +		 : :  "i" (&((char *)key)[branch]) : : l_yes);
> +
>  	return false;
>  l_yes:
>  	return true;