Re: [PATCH v3 06/18] xen/arm32: head: Replace "ldr rX, =<label>" with "mov_w rX, <label>"

From: Stefano Stabellini <sstabellini@kernel.org>
To: Julien Grall <julien@xen.org>
Cc: xen-devel@lists.xenproject.org, michal.orzel@amd.com,
	 Luca.Fancellu@arm.com, Julien Grall <jgrall@amazon.com>,
	 Stefano Stabellini <sstabellini@kernel.org>,
	 Bertrand Marquis <bertrand.marquis@arm.com>,
	 Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [PATCH v3 06/18] xen/arm32: head: Replace "ldr rX, =<label>" with "mov_w rX, <label>"
Date: Mon, 12 Dec 2022 16:31:39 -0800 (PST)	[thread overview]
Message-ID: <alpine.DEB.2.22.394.2212121631330.3075842@ubuntu-linux-20-04-desktop> (raw)
In-Reply-To: <20221212095523.52683-7-julien@xen.org>

On Mon, 12 Dec 2022, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
> 
> "ldr rX, =<label>" is used to load a value from the literal pool. This
> implies a memory access.
> 
> This can be avoided by using the macro mov_w which encode the value in
> the immediate of two instructions.
> 
> So replace all "ldr rX, =<label>" with "mov_w rX, <label>".
> 
> No functional changes intended.
> 
> Signed-off-by: Julien Grall <jgrall@amazon.com>

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


> ---
> 
>     Changes in v3:
>         * Patch added
> ---
>  xen/arch/arm/arm32/head.S | 38 +++++++++++++++++++-------------------
>  1 file changed, 19 insertions(+), 19 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index a558c2a6876e..ce680be91be1 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -62,7 +62,7 @@
>  .endm
>  
>  .macro load_paddr rb, sym
> -        ldr   \rb, =\sym
> +        mov_w \rb, \sym
>          add   \rb, \rb, r10
>  .endm
>  
> @@ -149,7 +149,7 @@ past_zImage:
>          mov   r8, r2                 /* r8 := DTB base address */
>  
>          /* Find out where we are */
> -        ldr   r0, =start
> +        mov_w r0, start
>          adr   r9, start              /* r9  := paddr (start) */
>          sub   r10, r9, r0            /* r10 := phys-offset */
>  
> @@ -170,7 +170,7 @@ past_zImage:
>          bl    enable_mmu
>  
>          /* We are still in the 1:1 mapping. Jump to the runtime Virtual Address. */
> -        ldr   r0, =primary_switched
> +        mov_w r0, primary_switched
>          mov   pc, r0
>  primary_switched:
>          /*
> @@ -190,7 +190,7 @@ primary_switched:
>          /* Setup the arguments for start_xen and jump to C world */
>          mov   r0, r10                /* r0 := Physical offset */
>          mov   r1, r8                 /* r1 := paddr(FDT) */
> -        ldr   r2, =start_xen
> +        mov_w r2, start_xen
>          b     launch
>  ENDPROC(start)
>  
> @@ -198,7 +198,7 @@ GLOBAL(init_secondary)
>          cpsid aif                    /* Disable all interrupts */
>  
>          /* Find out where we are */
> -        ldr   r0, =start
> +        mov_w r0, start
>          adr   r9, start              /* r9  := paddr (start) */
>          sub   r10, r9, r0            /* r10 := phys-offset */
>  
> @@ -227,7 +227,7 @@ GLOBAL(init_secondary)
>  
>  
>          /* We are still in the 1:1 mapping. Jump to the runtime Virtual Address. */
> -        ldr   r0, =secondary_switched
> +        mov_w r0, secondary_switched
>          mov   pc, r0
>  secondary_switched:
>          /*
> @@ -236,7 +236,7 @@ secondary_switched:
>           *
>           * XXX: This is not compliant with the Arm Arm.
>           */
> -        ldr   r4, =init_ttbr         /* VA of HTTBR value stashed by CPU 0 */
> +        mov_w r4, init_ttbr          /* VA of HTTBR value stashed by CPU 0 */
>          ldrd  r4, r5, [r4]           /* Actual value */
>          dsb
>          mcrr  CP64(r4, r5, HTTBR)
> @@ -254,7 +254,7 @@ secondary_switched:
>  #endif
>          PRINT("- Ready -\r\n")
>          /* Jump to C world */
> -        ldr   r2, =start_secondary
> +        mov_w r2, start_secondary
>          b     launch
>  ENDPROC(init_secondary)
>  
> @@ -297,8 +297,8 @@ ENDPROC(check_cpu_mode)
>   */
>  zero_bss:
>          PRINT("- Zero BSS -\r\n")
> -        ldr   r0, =__bss_start       /* r0 := vaddr(__bss_start) */
> -        ldr   r1, =__bss_end         /* r1 := vaddr(__bss_start) */
> +        mov_w r0, __bss_start        /* r0 := vaddr(__bss_start) */
> +        mov_w r1, __bss_end          /* r1 := vaddr(__bss_start) */
>  
>          mov   r2, #0
>  1:      str   r2, [r0], #4
> @@ -330,8 +330,8 @@ cpu_init:
>  
>  cpu_init_done:
>          /* Set up memory attribute type tables */
> -        ldr   r0, =MAIR0VAL
> -        ldr   r1, =MAIR1VAL
> +        mov_w r0, MAIR0VAL
> +        mov_w r1,MAIR1VAL
>          mcr   CP32(r0, HMAIR0)
>          mcr   CP32(r1, HMAIR1)
>  
> @@ -341,10 +341,10 @@ cpu_init_done:
>           * PT walks are write-back, write-allocate in both cache levels,
>           * Full 32-bit address space goes through this table.
>           */
> -        ldr   r0, =(TCR_RES1|TCR_SH0_IS|TCR_ORGN0_WBWA|TCR_IRGN0_WBWA|TCR_T0SZ(0))
> +        mov_w r0, (TCR_RES1|TCR_SH0_IS|TCR_ORGN0_WBWA|TCR_IRGN0_WBWA|TCR_T0SZ(0))
>          mcr   CP32(r0, HTCR)
>  
> -        ldr   r0, =HSCTLR_SET
> +        mov_w r0, HSCTLR_SET
>          mcr   CP32(r0, HSCTLR)
>          isb
>  
> @@ -452,7 +452,7 @@ ENDPROC(cpu_init)
>   */
>  create_page_tables:
>          /* Prepare the page-tables for mapping Xen */
> -        ldr   r0, =XEN_VIRT_START
> +        mov_w r0, XEN_VIRT_START
>          create_table_entry boot_pgtable, boot_second, r0, 1
>          create_table_entry boot_second, boot_third, r0, 2
>  
> @@ -576,7 +576,7 @@ remove_identity_mapping:
>          cmp   r1, #XEN_FIRST_SLOT
>          beq   1f
>          /* It is not in slot 0, remove the entry */
> -        ldr   r0, =boot_pgtable      /* r0 := root table */
> +        mov_w r0, boot_pgtable       /* r0 := root table */
>          lsl   r1, r1, #3             /* r1 := Slot offset */
>          strd  r2, r3, [r0, r1]
>          b     identity_mapping_removed
> @@ -590,7 +590,7 @@ remove_identity_mapping:
>          cmp   r1, #XEN_SECOND_SLOT
>          beq   identity_mapping_removed
>          /* It is not in slot 1, remove the entry */
> -        ldr   r0, =boot_second       /* r0 := second table */
> +        mov_w r0, boot_second        /* r0 := second table */
>          lsl   r1, r1, #3             /* r1 := Slot offset */
>          strd  r2, r3, [r0, r1]
>  
> @@ -620,7 +620,7 @@ ENDPROC(remove_identity_mapping)
>  setup_fixmap:
>  #if defined(CONFIG_EARLY_PRINTK)
>          /* Add UART to the fixmap table */
> -        ldr   r0, =EARLY_UART_VIRTUAL_ADDRESS
> +        mov_w r0, EARLY_UART_VIRTUAL_ADDRESS
>          create_mapping_entry xen_fixmap, r0, r11, type=PT_DEV_L3
>  #endif
>          /* Map fixmap into boot_second */
> @@ -643,7 +643,7 @@ ENDPROC(setup_fixmap)
>   * Clobbers r3
>   */
>  launch:
> -        ldr   r3, =init_data
> +        mov_w r3, init_data
>          add   r3, #INITINFO_stack    /* Find the boot-time stack */
>          ldr   sp, [r3]
>          add   sp, #STACK_SIZE        /* (which grows down from the top). */
> -- 
> 2.38.1
>