linux-kernel - Re: [PATCH v2 01/13] openrisc: Add gcc machine instruction flag configuration

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Date:   Wed, 18 May 2022 06:27:07 +0900
From:   Stafford Horne <shorne@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Openrisc <openrisc@...ts.librecores.org>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
Subject: Re: [PATCH v2 01/13] openrisc: Add gcc machine instruction flag
 configuration

On Tue, May 17, 2022 at 09:54:58AM +0900, Stafford Horne wrote:
> OpenRISC GCC supports flags to enable the backend to output instructions
> if they are supported by a target processor.  This patch adds
> configuration flags to enable configuring these flags to tune the kernel
> for a particular CPU configuration.
> 
> In the future we could also enable all of these flags by default and
> provide instruction emulation in the kernel to make these choices easier
> for users but this is what we provide for now.
> 
> Signed-off-by: Stafford Horne <shorne@...il.com>
> ---
>  arch/openrisc/Kconfig  | 53 ++++++++++++++++++++++++++++++++++++++++++
>  arch/openrisc/Makefile | 17 ++++++++++++++
>  2 files changed, 70 insertions(+)
> 
> diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
> index 0d68adf6e02b..ea7eac20911a 100644
> --- a/arch/openrisc/Kconfig
> +++ b/arch/openrisc/Kconfig
> @@ -114,6 +114,59 @@ config OPENRISC_HAVE_INST_DIV
>  	default y
>  	help
>  	  Select this if your implementation has a hardware divide instruction
> +
> +config OPENRISC_HAVE_INST_CMOV
> +	bool "Have instruction l.cmov for conditional move"
> +	default y
> +	help
> +	  This config enables gcc to generate l.cmov instructions when compiling
> +	  the kernel which in general will improve performance and reduce the
> +	  binary size.
> +
> +	  Select this if your implementation has support for the Class II
> +	  l.cmov conistional move instruction.
> +
> +	  Say N if you are unsure.
> +
> +config OPENRISC_HAVE_INST_ROR
> +	bool "Have instruction l.ror for rotate right"
> +	default y
> +	help
> +	  This config enables gcc to generate l.ror instructions when compiling
> +	  the kernel which in general will improve performance and reduce the
> +	  binary size.
> +
> +	  Select this if your implementation has support for the Class II
> +	  l.ror rotate right instruction.
> +
> +	  Say N if you are unsure.
> +
> +config OPENRISC_HAVE_INST_RORI
> +	bool "Have instruction l.rori for rotate right with immediate"
> +	default y
> +	help
> +	  This config enables gcc to generate l.rori instructions when compiling
> +	  the kernel which in general will improve performance and reduce the
> +	  binary size.
> +
> +	  Select this if your implementation has support for the Class II
> +	  l.rori rotate right with immediate instruction.
> +
> +	  Say N if you are unsure.
> +
> +config OPENRISC_HAVE_INST_SEXT
> +	bool "Have instructions l.ext* for sign extension"
> +	default y
> +	help
> +	  This config enables gcc to generate l.ext* instructions when compiling
> +	  the kernel which in general will improve performance and reduce the
> +	  binary size.
> +
> +	  Select this if your implementation has support for the Class II
> +	  l.exths, l.extbs, l.exthz and l.extbz size extend instructions.
> +
> +	  Say N if you are unsure.

Looking at this again and when generating the defconfig, the default for these
should be no,

-Stafford

> +
>  endmenu
>  
>  config NR_CPUS
> diff --git a/arch/openrisc/Makefile b/arch/openrisc/Makefile
> index 760b734fb822..b446510173cd 100644
> --- a/arch/openrisc/Makefile
> +++ b/arch/openrisc/Makefile
> @@ -21,6 +21,7 @@ OBJCOPYFLAGS    := -O binary -R .note -R .comment -S
>  LIBGCC 		:= $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
>  
>  KBUILD_CFLAGS	+= -pipe -ffixed-r10 -D__linux__
> +KBUILD_CFLAGS	+= -msfimm -mshftimm
>  
>  all: vmlinux.bin
>  
> @@ -38,6 +39,22 @@ else
>  	KBUILD_CFLAGS += $(call cc-option,-msoft-div)
>  endif
>  
> +ifeq ($(CONFIG_OPENRISC_HAVE_INST_CMOV),y)
> +	KBUILD_CFLAGS += $(call cc-option,-mcmov)
> +endif
> +
> +ifeq ($(CONFIG_OPENRISC_HAVE_INST_ROR),y)
> +	KBUILD_CFLAGS += $(call cc-option,-mror)
> +endif
> +
> +ifeq ($(CONFIG_OPENRISC_HAVE_INST_RORI),y)
> +	KBUILD_CFLAGS += $(call cc-option,-mrori)
> +endif
> +
> +ifeq ($(CONFIG_OPENRISC_HAVE_INST_SEXT),y)
> +	KBUILD_CFLAGS += $(call cc-option,-msext)
> +endif
> +
>  head-y 		:= arch/openrisc/kernel/head.o
>  
>  libs-y		+= $(LIBGCC)
> -- 
> 2.31.1
>