make the code simpler

From: Du Huanpeng <[email protected]>

Signed-off-by Du Huanpeng <[email protected]>

---
 arch/mips/boot/start.S |   26 +++-----------------------
 1 file changed, 3 insertions(+), 23 deletions(-)

arch/mips/boot/start.S +3 -23

index 7e2ae5e..474407d 100644
@@ -25,26 +25,6 @@
 #include <generated/compile.h>
 #include <generated/utsrelease.h>
 
-	/*
-	 * ADR macro instruction (inspired by ARM)
-	 *
-	 * ARM architecture doesn't have PC-relative jump instruction
-	 * like MIPS' B/BAL insns.  When ARM makes PC-relative jumps,
-	 * it uses ADR insn.  ADR is used to get a destination address
-	 * of 'label' against current PC.  With this, ARM can safely
-	 * make PC-relative jumps.
-	 */
-	.macro	ADR rd label temp
-	.set	push
-	.set	noreorder
-	move	\temp, ra			# preserve ra beforehand
-	bal	_pc
-	 nop
-_pc:	addiu	\rd, ra, \label - _pc		# label is assumed to be
-	move	ra, \temp			# within pc +/- 32KB
-	.set	pop
-	.endm
-
 	.set noreorder
 	.text
 	.section ".text_bare_init"

@@ -52,8 +32,9 @@ _pc:	addiu	\rd, ra, \label - _pc		# label is assumed to be
 
 EXPORT(_start)
 
-	b	__start
+	bal	__start
 	 nop
+_ra: 
 
 	.org	0x10
 	.ascii	"barebox " UTS_RELEASE " " UTS_VERSION

@@ -72,8 +53,7 @@ __start:
 	mtc0	k0, CP0_STATUS
 
 	/* copy barebox to link location */
-	ADR	a0, _start, t1	/* a0 <- pc-relative position of _start */
-
+	addiu	a0, ra, (_start - _ra)	/*a0 <- pc-relative position of _start  */
 	la	a1, _start	/* link (RAM) _start address */
 
 	beq	a0, a1, stack_setup

Signature · 7 lines

1.7.9.5


_______________________________________________
barebox mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/barebox

I am trying to port barebox on my TP-LINK WR720N router (SoC: AR9331 24KC, DRAM: 32MiB, FLASH: 4MiB)

In the start.S, this ADR macro make me confuse...
But finally, I find it
.macro ADR rd label temp
just used to get the label's VMA. (correct me if I am wrong) . in the start.S, it wants to get the _start 's VMA.
Assuming the _start is the first instruction of barebox.
Why not save the _start's VMA to ra when running the first instruction? By

	bal __start
	nop
	...
	__start:

I think the different between above and ADR is:
My code overwrite the ra register.
If any other bootloader or something call's barebox, It can't return.

Quoted 1 line

Personally I have no objections on removing ADR macro.

Just remove it from start.S

By the way, I really need help...
Do you interested in porting barebox to ar9331?
The router is quite cute and small, and very cheap!
Just 125CNY, (20USD).
You can find quit a lot information about it on OpenWRT. And there is a working u-boot for this router.
https://github.com/pepe2k/u-boot_mod
I have modify this u-boot and make it run In the kernel's position.
https://github.com/zhang3/u-boot_mod
So that the original u-boot can boot my u-boot.
By done this,
I modify the link address of barebox the same as the u-boot(second one).

-----邮件原件-----
发件人: Antony Pavlov [mailto:[email protected]]
发送时间: 2013年12月5日 0:34
收件人: Kevin Du Huanpeng
主题: Re: [PATCH] MIPS: start.S: remove duplicate ADR macro definition

Quoted 3 lines · On Wed, 4 Dec 2013 20:47:47 +0800 Kevin Du Huanpeng <[email protected]> wrote:

hi, mips has a b/bal, why does mips have to use the macro: ADR in the start.S

Personally I have no objections on removing ADR macro. It has some disadvantages (e.g. it can't be used twice in one program because it uses global label).

If you want understand the situation with ADR macro you shoul track the MIPS barebox history.

My original MIPS barebox has no ADR macro. See head.S file and especialy 'compute_offset' label in this patch
http://lists.infradead.org/pipermail/barebox/2011-June/003695.html

But after my publication Shinya Kuribayashi has appeared:
http://lists.infradead.org/pipermail/barebox/2011-June/003707.html

Kuribayashi-san has his own (but not working) mips barebox implementation and Jean-Christophe enforced me to use Kuribayashi's start.S realisation (with ADR macro):
http://lists.infradead.org/pipermail/barebox/2011-June/003715.html

As a result now we have start.S with ADR macro.

You want drop ADR macro from start.S, but IMHO we can drop relocation code from start.S completely!
Today we have smart PBL (pre-boot loader) in barebox. This PBL can comress and relocate main barebox image. So we can easely drop relocation code from start.S:
if you need relocation then just simply use PBL!

Can you please describe your interest in barebox for MIPS? That type of board do you use?

If you need any help on barebox for MIPS you are welcome!

Quoted 50 lines

_start: bal __start
nop
__start:
addiu a0, ra, -8
a0, now is the _start's vma.

2013/12/4 Antony Pavlov <[email protected]>:

Quoted 42 lines

Signed-off-by Antony Pavlov <[email protected]>

---
 arch/mips/boot/start.S | 22 +---------------------
 1 file changed, 1 insertion(+), 21 deletions(-)

arch/mips/boot/start.S index renamed from arch/mips/boot/start.S +0 -0

7e2ae5e..d180157 100644

arch/mips/boot/start.S +0 -1

@@ -2,7 +2,6 @@
  * Startup Code for MIPS CPU
  *
  * Copyright (C) 2011 Antony Pavlov <[email protected]>
- * Used code copyrighted (C) 2009 by Shinya Kuribayashi <[email protected]>
  *
  * This file is part of barebox.
  * See file CREDITS for list of people who contributed to this project.

@@ -24,26 +23,7 @@
 #include <asm-generic/memory_layout.h>  #include 

<generated/compile.h> #include <generated/utsrelease.h>

arch/mips/boot/start.S +1 -20

-
-       /*
-        * ADR macro instruction (inspired by ARM)
-        *
-        * ARM architecture doesn't have PC-relative jump instruction
-        * like MIPS' B/BAL insns.  When ARM makes PC-relative jumps,
-        * it uses ADR insn.  ADR is used to get a destination address
-        * of 'label' against current PC.  With this, ARM can safely
-        * make PC-relative jumps.
-        */
-       .macro  ADR rd label temp
-       .set    push
-       .set    noreorder
-       move    \temp, ra                       # preserve ra beforehand
-       bal     _pc
-        nop
-_pc:   addiu   \rd, ra, \label - _pc           # label is assumed to be
-       move    ra, \temp                       # within pc +/- 32KB
-       .set    pop
-       .endm
+#include <asm/pbl_macros.h>

Quoted 5 lines

Quoted 5 lines

.set noreorder
.text
--
1.8.4.4

--
--
Best regards,
Antony Pavlov