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From: Stefano Stabellini <sstabellini@kernel.org>
To: Julien Grall <julien.grall@arm.com>
Cc: xen-devel@lists.xenproject.org,
	Stefano Stabellini <sstabellini@kernel.org>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [PATCH v2 19/35] xen/arm32: head: Add a macro to move an immediate constant into a 32-bit register
Date: Tue, 30 Jul 2019 14:11:46 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.21.1907301327070.28600@sstabellini-ThinkPad-T480s> (raw)
In-Reply-To: <20190722213958.5761-20-julien.grall@arm.com>

On Mon, 22 Jul 2019, Julien Grall wrote:
> The current boot code is using the pattern ldr rX, =... to move an
> immediate constant into a 32-bit register.
> 
> This pattern implies to load the immediate constant from a literal pool,
> meaning a memory access will be performed.
> 
> The memory access can be avoided by using movw/movt instructions.
> 
> A new macro is introduced to move an immediate constant into a 32-bit
> register without a memory load. Follow-up patches will make use of it.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>

That's interesting!

Acked-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
>     Changes in v2:
>         - Patch added
> ---
>  xen/arch/arm/arm32/head.S | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 18ded49a04..99f4af18d8 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -37,6 +37,15 @@
>  #endif
>  
>  /*
> + * Move an immediate constant into a 32-bit register using movw/movt
> + * instructions.
> + */
> +.macro mov_w reg, word
> +        movw  \reg, #:lower16:\word
> +        movt  \reg, #:upper16:\word
> +.endm
> +
> +/*
>   * Common register usage in this file:
>   *   r0  -
>   *   r1  -
> -- 
> 2.11.0
> 

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  reply	other threads:[~2019-07-30 21:12 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-22 21:39 [Xen-devel] [PATCH v2 00/35] xen/arm: Rework head.S to make it more compliant with the Arm Arm Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 01/35] xen/arm64: macros: Introduce an assembly macro to alias x30 Julien Grall
2019-07-26 14:28   ` Volodymyr Babchuk
2019-07-29 23:11   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 02/35] xen/arm64: head: Mark the end of subroutines with ENDPROC Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 03/35] xen/arm64: head: Don't clobber x30/lr in the macro PRINT Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 04/35] xen/arm64: head: Rework UART initialization on boot CPU Julien Grall
2019-07-29 23:19   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 05/35] xen/arm64: head: Introduce print_reg Julien Grall
2019-07-29 23:36   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 06/35] xen/arm64: head: Introduce distinct paths for the boot CPU and secondary CPUs Julien Grall
2019-07-30 17:06   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 07/35] xen/arm64: head: Rework and document check_cpu_mode() Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 08/35] xen/arm64: head: Rework and document zero_bss() Julien Grall
2019-07-30 17:13   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 09/35] xen/arm64: head: Improve coding style and document cpu_init() Julien Grall
2019-07-30 17:14   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 10/35] xen/arm64: head: Improve coding style and document create_pages_tables() Julien Grall
2019-07-30 17:15   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 11/35] xen/arm64: head: Document enable_mmu() Julien Grall
2019-07-30 17:20   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 12/35] xen/arm64: head: Move assembly switch to the runtime PT in secondary CPUs path Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 13/35] xen/arm64: head: Don't setup the fixmap on secondary CPUs Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 14/35] xen/arm64: head: Remove 1:1 mapping as soon as it is not used Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 15/35] xen/arm64: head: Rework and document setup_fixmap() Julien Grall
2019-07-30 17:40   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 16/35] xen/arm64: head: Rework and document launch() Julien Grall
2019-07-30 17:45   ` Stefano Stabellini
2019-07-31 20:13     ` Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 17/35] xen/arm64: head: Setup TTBR_EL2 in enable_mmu() and add missing isb Julien Grall
2019-07-30 18:20   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 18/35] xen/arm64: head: Introduce a macro to get a PC-relative address of a symbol Julien Grall
2019-07-30 18:24   ` Stefano Stabellini
2019-07-30 19:55     ` Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 19/35] xen/arm32: head: Add a macro to move an immediate constant into a 32-bit register Julien Grall
2019-07-30 21:11   ` Stefano Stabellini [this message]
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 20/35] xen/arm32: head: Mark the end of subroutines with ENDPROC Julien Grall
2019-07-30 19:22   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 21/35] xen/arm32: head: Don't clobber r14/lr in the macro PRINT Julien Grall
2019-07-30 19:34   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 22/35] xen/arm32: head: Rework UART initialization on boot CPU Julien Grall
2019-07-30 19:40   ` Stefano Stabellini
2019-07-31 20:18     ` Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 23/35] xen/arm32: head: Introduce print_reg Julien Grall
2019-07-30 19:43   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 24/35] xen/arm32: head: Introduce distinct paths for the boot CPU and secondary CPUs Julien Grall
2019-07-30 20:07   ` Stefano Stabellini
2019-07-31 20:31     ` Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 25/35] xen/arm32: head: Rework and document check_cpu_mode() Julien Grall
2019-07-30 20:10   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 26/35] xen/arm32: head: Rework and document zero_bss() Julien Grall
2019-07-30 20:14   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 27/35] xen/arm32: head: Document create_pages_tables() Julien Grall
2019-07-30 20:18   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 28/35] xen/arm32: head: Document enable_mmu() Julien Grall
2019-07-30 20:19   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 29/35] xen/arm32: head: Move assembly switch to the runtime PT in secondary CPUs path Julien Grall
2019-07-30 20:25   ` Stefano Stabellini
2019-07-30 20:54     ` Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 30/35] xen/arm32: head: Don't setup the fixmap on secondary CPUs Julien Grall
2019-07-30 20:38   ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 31/35] xen/arm32: head: Remove 1:1 mapping as soon as it is not used Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 32/35] xen/arm32: head: Rework and document setup_fixmap() Julien Grall
2019-07-30 21:14   ` Stefano Stabellini
2019-07-31 20:42     ` Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 33/35] xen/arm32: head: Rework and document launch() Julien Grall
2019-07-30 21:21   ` Stefano Stabellini
2019-07-30 21:34     ` Julien Grall
2019-07-31 20:27       ` Stefano Stabellini
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 34/35] xen/arm32: head: Setup HTTBR in enable_mmu() and add missing isb Julien Grall
2019-07-30 21:26   ` Stefano Stabellini
2019-07-31 21:01     ` Julien Grall
2019-07-22 21:39 ` [Xen-devel] [PATCH v2 35/35] xen/arm: Zero BSS after the MMU and D-cache is turned on Julien Grall
2019-07-30 21:30   ` Stefano Stabellini

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