linux-kernel - Re: [PATCH v11 4/5] jump_label: adjust inline asm to be consistent

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Message-ID: <mhng-0614da52-c420-4be1-a5b9-64dacae91d0e@palmer-ri-x1c9a>
Date: Thu, 17 Oct 2024 12:32:13 -0700 (PDT)
From: Palmer Dabbelt <palmer@...belt.com>
To: aliceryhl@...gle.com
CC: rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
  peterz@...radead.org, jpoimboe@...nel.org, jbaron@...mai.com, Ard Biesheuvel <ardb@...nel.org>,
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  Conor Dooley <conor.dooley@...rochip.com>, samuel.holland@...ive.com, linux-riscv@...ts.infradead.org,
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  akpm@...ux-foundation.org, zhaotianrui@...ngson.cn, loongarch@...ts.linux.dev, aliceryhl@...gle.com
Subject:     Re: [PATCH v11 4/5] jump_label: adjust inline asm to be consistent

On Tue, 15 Oct 2024 06:14:58 PDT (-0700), aliceryhl@...gle.com wrote:
> To avoid duplication of inline asm between C and Rust, we need to
> import the inline asm from the relevant `jump_label.h` header into Rust.
> To make that easier, this patch updates the header files to expose the
> inline asm via a new ARCH_STATIC_BRANCH_ASM macro.
>
> The header files are all updated to define a ARCH_STATIC_BRANCH_ASM that
> takes the same arguments in a consistent order so that Rust can use the
> same logic for every architecture.
>
> Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Co-developed-by: Miguel Ojeda <ojeda@...nel.org>
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
>  arch/arm/include/asm/jump_label.h       | 14 +++++----
>  arch/arm64/include/asm/jump_label.h     | 20 ++++++++-----
>  arch/loongarch/include/asm/jump_label.h | 16 +++++++----
>  arch/riscv/include/asm/jump_label.h     | 50 ++++++++++++++++++---------------
>  arch/x86/include/asm/jump_label.h       | 35 +++++++++--------------
>  5 files changed, 73 insertions(+), 62 deletions(-)

[...]

> diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/jump_label.h
> index 1c768d02bd0c..87a71cc6d146 100644
> --- a/arch/riscv/include/asm/jump_label.h
> +++ b/arch/riscv/include/asm/jump_label.h
> @@ -16,21 +16,28 @@
>
>  #define JUMP_LABEL_NOP_SIZE 4
>
> +#define JUMP_TABLE_ENTRY(key, label)			\
> +	".pushsection	__jump_table, \"aw\"	\n\t"	\
> +	".align		" RISCV_LGPTR "		\n\t"	\
> +	".long		1b - ., " label " - .	\n\t"	\
> +	"" RISCV_PTR "	" key " - .		\n\t"	\
> +	".popsection				\n\t"
> +
> +/* This macro is also expanded on the Rust side. */
> +#define ARCH_STATIC_BRANCH_ASM(key, label)		\
> +	"	.align		2		\n\t"	\
> +	"	.option push			\n\t"	\
> +	"	.option norelax			\n\t"	\
> +	"	.option norvc			\n\t"	\
> +	"1:	nop				\n\t"	\
> +	"	.option pop			\n\t"	\
> +	JUMP_TABLE_ENTRY(key, label)
> +
>  static __always_inline bool arch_static_branch(struct static_key * const key,
>  					       const bool branch)
>  {
>  	asm goto(
> -		"	.align		2			\n\t"
> -		"	.option push				\n\t"
> -		"	.option norelax				\n\t"
> -		"	.option norvc				\n\t"
> -		"1:	nop					\n\t"
> -		"	.option pop				\n\t"
> -		"	.pushsection	__jump_table, \"aw\"	\n\t"
> -		"	.align		" RISCV_LGPTR "		\n\t"
> -		"	.long		1b - ., %l[label] - .	\n\t"
> -		"	" RISCV_PTR "	%0 - .			\n\t"
> -		"	.popsection				\n\t"
> +		ARCH_STATIC_BRANCH_ASM("%0", "%l[label]")
>  		:  :  "i"(&((char *)key)[branch]) :  : label);
>
>  	return false;
> @@ -38,21 +45,20 @@ static __always_inline bool arch_static_branch(struct static_key * const key,
>  	return true;
>  }
>
> +#define ARCH_STATIC_BRANCH_JUMP_ASM(key, label)		\
> +	"	.align		2		\n\t"	\
> +	"	.option push			\n\t"	\
> +	"	.option norelax			\n\t"	\
> +	"	.option norvc			\n\t"	\
> +	"1:	j	" label "		\n\t" \
> +	"	.option pop			\n\t"	\
> +	JUMP_TABLE_ENTRY(key, label)
> +
>  static __always_inline bool arch_static_branch_jump(struct static_key * const key,
>  						    const bool branch)
>  {
>  	asm goto(
> -		"	.align		2			\n\t"
> -		"	.option push				\n\t"
> -		"	.option norelax				\n\t"
> -		"	.option norvc				\n\t"
> -		"1:	j		%l[label]		\n\t"
> -		"	.option pop				\n\t"
> -		"	.pushsection	__jump_table, \"aw\"	\n\t"
> -		"	.align		" RISCV_LGPTR "		\n\t"
> -		"	.long		1b - ., %l[label] - .	\n\t"
> -		"	" RISCV_PTR "	%0 - .			\n\t"
> -		"	.popsection				\n\t"
> +		ARCH_STATIC_BRANCH_JUMP_ASM("%0", "%l[label]")
>  		:  :  "i"(&((char *)key)[branch]) :  : label);
>
>  	return false;

Acked-by: Palmer Dabbelt <palmer@...osinc.com> # RISC-V