[PATCH 1/6] ARM: compressed: move sharpsl startup code into subroutine

[linux@armlinux.org.uk (Russell King - ARM Linux)]

On Mon, Nov 05, 2018 at 07:44:33PM +0100, Ard Biesheuvel wrote:
> Instead of relying on unspecified linker behavior, move the
> SharpSL startup code into a subroutine and call it from the
> location we expect the linker to put the code.

Why is it "unspecified linker behaviour" ?  Lots of libraries and
programs rely on the linker building tables, whether it be data or
code from sections.

For example, programs build a section called .init which starts with
the code in crti.o, code from other files, and finishes with code
from crtn.o.

crti.o:

Disassembly of section .init:

00000000 <_init>:
   0:   e92d4008        push    {r3, lr}
   4:   ebfffffe        bl      0 <_init>
                        4: R_ARM_CALL   call_weak_fn

crtn.o:

Disassembly of section .init:

00000000 <.init>:
   0:   e8bd8008        pop     {r3, pc}

So, I don't think there's anything "unspecified" here.

We also rely heavily on this in the kernel to build exception tables,
symbol tables, and so forth.

> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  arch/arm/boot/compressed/head-sharpsl.S | 24 ++++++++++----------
>  arch/arm/boot/compressed/head.S         |  3 +++
>  2 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm/boot/compressed/head-sharpsl.S b/arch/arm/boot/compressed/head-sharpsl.S
> index 992e784500fa..f4e6ad318376 100644
> --- a/arch/arm/boot/compressed/head-sharpsl.S
> +++ b/arch/arm/boot/compressed/head-sharpsl.S
> @@ -20,9 +20,10 @@
>  #error What am I doing here...
>  #endif
>  
> -		.section        ".start", "ax"
> +	.text
>  
> -__SharpSL_start:
> +ENTRY(__SharpSL_start)
> +	mov	ip, lr			@ preserve lr
>  
>  /* Check for TC6393 - if found we have a Tosa */
>  	ldr	r7, .TOSAID
> @@ -30,7 +31,7 @@ __SharpSL_start:
>  	mov 	r6, #0x03
>  	ldrh	r3, [r1, #8]		@ Load TC6393XB Revison: This is 0x0003
>  	cmp	r6, r3
> -	beq	.SHARPEND		@ Success -> tosa
> +	moveq	pc, ip			@ Success -> tosa
>  
>  /* Check for pxa270 - if found, branch */
>  	mrc p15, 0, r4, c0, c0		@ Get Processor ID
> @@ -55,30 +56,30 @@ __SharpSL_start:
>  	ldr	r3, .W100ID
>  	ldr	r7, .POODLEID
>  	cmp	r6, r3
> -	bne	.SHARPEND			@ We have no w100 - Poodle
> +	movne	pc, ip				@ We have no w100 - Poodle
>  
>  /* Check for pxa250 - if found we have a Corgi */
>  	ldr	r7, .CORGIID
>  	ldr	r3, .PXA255ID
>  	cmp	r4, r3
> -	blo	.SHARPEND			@ We have a PXA250 - Corgi
> +	movlo	pc, ip				@ We have a PXA250 - Corgi
>  
>  /* Check for 64MiB flash - if found we have a Shepherd */
>  	bl	get_flash_ids
>  	ldr	r7, .SHEPHERDID
>  	cmp	r3, #0x76			@ 64MiB flash
> -	beq	.SHARPEND			@ We have Shepherd
> +	moveq	pc, ip				@ We have Shepherd
>  
>  /* Must be a Husky */
>  	ldr	r7, .HUSKYID		@ Must be Husky
> -	b .SHARPEND
> +	mov	pc, ip			@ return
>  
>  .PXA270:
>  /* Check for 16MiB flash - if found we have Spitz */
>  	bl	get_flash_ids
>  	ldr	r7, .SPITZID
>  	cmp	r3, #0x73			@ 16MiB flash
> -	beq	.SHARPEND			@ We have Spitz
> +	moveq	pc, ip				@ We have Spitz
>  
>  /* Check for a second SCOOP chip - if found we have Borzoi */
>  	ldr	r1, .SCOOP2ADDR
> @@ -87,11 +88,12 @@ __SharpSL_start:
>  	strh	r6, [r1]
>  	ldrh	r6, [r1]
>  	cmp	r6, #0x0140
> -	beq	.SHARPEND			@ We have Borzoi
> +	moveq	pc, ip				@ We have Borzoi
>  
>  /* Must be Akita */
>  	ldr	r7, .AKITAID
> -	b	.SHARPEND			@ We have Borzoi
> +	mov	pc, ip				@ We have Borzoi
> +ENDPROC(__SharpSL_start)
>  
>  .PXA255ID:
>  	.word	0x69052d00		@ PXA255 Processor ID
> @@ -147,5 +149,3 @@ get_flash_ids:
>  	ldrb	r2, [r1, #20]		@ NAND Manufacturer ID
>  	ldrb	r3, [r1, #20]		@ NAND Chip ID
>  	mov	pc, lr
> -
> -.SHARPEND:
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 6c7ccb428c07..5067f287fa5a 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -213,6 +213,9 @@ not_angel:
>  		 */
>  
>  		.text
> +#ifdef CONFIG_PXA_SHARPSL_DETECT_MACH_ID
> +		bl	__SharpSL_start
> +#endif
>  
>  #ifdef CONFIG_AUTO_ZRELADDR
>  		/*
> -- 
> 2.19.1
> 

-- 
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