Re: some questions about arch/arm/boot/compress/head.s

[Khem Raj <raj dot khem at gmail dot com>]

On (11/10/08 14:31), loody wrote:
> Dear all:
> I try to trace kernel source, head.s, and there are some questions I
> need your help.
> Below I excerpt some part of it.
> 
> start:
> 		.type	start,#function
> 		.rept	8
> 		mov	r0, r0
> 		.endr
> 
> 		b	1f
> 		.word 0x016f2818		@ Magic numbers to help the loader
> 		.word	 start			@ absolute load/run zImage address
> 		.word	 _edata			@ zImage end address
> 1:		mov	r7, r1			@ save architecture ID
> 		mov	r8, r2			@ save atags pointer
> ......
> ......
> .text
> 		adr	r0, LC0
> 		
> 
> My questions are:
> 1. what does "b     1f" and "b    1b" means?
>    I have grep the head.s and there is no label named, 1f or 1b.
>    And in GAS manual there seems no explanation about "b", since b is
> arm's instructions, branch.
>    I also check arm-reference manual, chapter a5, and there is no
> mention about this kind of addressing mode, either.

read
http://sourceware.org/binutils/docs-2.18/as/Symbol-Names.html#Symbol-Names

> 
> 2. what is adr used for?
> It seems not arm instructions and I search the file for any macro
> definition but the result is fail.

read
http://sourceware.org/binutils/docs-2.18/as/ARM-Opcodes.html#ARM-Opcodes

> 
> 3. where I can find the parameter start, _edata defined?

I guess you are using ARM so its in kernel linker script. See
arch/arm/kernel/vmlinux.lds.S

> Does  the start in ".word start @ absolute load/run zImage address"
> mean this start label?

No it is asking the value of start to be put in there.


>

 
> appreciate your help in advance,
> miloody