linux-kernel - Re: [PATCH] MIPS: zboot: head.S clean up

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Date:   Mon, 21 Dec 2020 14:09:53 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-mips@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: zboot: head.S clean up

Hi Jiaxun,

Le lun. 21 déc. 2020 à 21:00, Jiaxun Yang <jiaxun.yang@...goat.com> a 
écrit :
> .cprestore is removed as we don't except Position Independent
> zboot ELF.
> 
> .noreorder is also removed and rest instructions is massaged
> to improve readability.
> 
> t9 register is used to indirect jump as MIPS ABI requirement.
> 
> Reported-by: Paul Cercueil <paul@...pouillou.net>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> ---
>  arch/mips/boot/compressed/head.S | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/mips/boot/compressed/head.S 
> b/arch/mips/boot/compressed/head.S
> index 409cb483a9ff..977218c90bc8 100644
> --- a/arch/mips/boot/compressed/head.S
> +++ b/arch/mips/boot/compressed/head.S
> @@ -15,8 +15,6 @@
>  #include <asm/asm.h>
>  #include <asm/regdef.h>
> 
> -	.set noreorder
> -	.cprestore
>  	LEAF(start)
>  start:

You can also remove the 'start' label, since it's declared inside the 
LEAF() macro as well. GNU's assembler won't mind, but LLVM will choke 
on that.

Cheers,
-Paul

>  	/* Save boot rom start args */
> @@ -35,21 +33,20 @@ start:
>  	PTR_LA	a0, (.heap)	     /* heap address */
>  	PTR_LA	sp, (.stack + 8192)  /* stack address */
> 
> -	PTR_LA	ra, 2f
> -	PTR_LA	k0, decompress_kernel
> -	jr	k0
> -	 nop
> +	PTR_LA	t9, decompress_kernel
> +	jalr	t9
> +
>  2:
>  	move	a0, s0
>  	move	a1, s1
>  	move	a2, s2
>  	move	a3, s3
> -	PTR_LI	k0, KERNEL_ENTRY
> -	jr	k0
> -	 nop
> +	PTR_LI	t9, KERNEL_ENTRY
> +	jalr	t9
> +
>  3:
>  	b	3b
> -	 nop
> +
>  	END(start)
> 
>  	.comm .heap,BOOT_HEAP_SIZE,4
> --
> 2.29.2
>