[PATCH] MIPS: zboot: head.S clean up

[PATCH] MIPS: zboot: head.S clean up

[Jiaxun Yang]

.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@crapouillou.net>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.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:
 	/* 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

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

[Paul Cercueil]

Hi Jiaxun,

Le lun. 21 déc. 2020 à 21:00, Jiaxun Yang <jiaxun.yang@flygoat.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@crapouillou.net>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.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
> 

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

[Jiaxun Yang]

On Mon, Dec 21, 2020, at 10:09 PM, Paul Cercueil wrote:
> Hi Jiaxun,
> 
> Le lun. 21 déc. 2020 à 21:00, Jiaxun Yang <jiaxun.yang@flygoat.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@crapouillou.net>
> > Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.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.

Thanks, will do in v2!

I was trying to catch you on IRC but failed every time when it comes to my mind :-(

> 
> Cheers,
> -Paul
> 

- Jiaxun