confusion about relocation (ARM)

Sascha Hauer s.hauer at
Mon Jan 4 07:07:58 EST 2010

On Fri, Jan 01, 2010 at 10:48:26PM +0100, Matthias Kaehlcke wrote:
> hi eric,
> thanks for your reply
> El Fri, Jan 01, 2010 at 09:36:29PM +0100 Eric Bénard ha dit:
> > Le 01/01/2010 20:48, Matthias Kaehlcke a écrit :
> >> a comment in start_barebox() says 'We are running from RAM now', so i
> >> deduced SDRAM must work. but after having a look at start-arm.S i'm a
> >> little bit confused. as far as i understand the barebox code is copied
> >> to RAM in copy_loop(). what i don't see is where the program counter
> >> is set to the address in RAM?
> >>
> > in arch/arm/cpu/start-arm.S @ line 245 :
> >         ldr     pc, _start_armboot
> i saw this line, but i don't understand how it comes that
> the address at _start_armboot points to RAM and not to the flash.

When your barebox image is linked to RAM (that is 0x05700000 in your
case) _start_armboot is in RAM, too.

> another question: how does ARCH_TEXT_BASE fit in here? i defined it as
> 0x05700000, but in the barebox image _TEXT_BASE is 0x00000000

Have a look at barebox.S, it should look like:

barebox:     file format elf32-littlearm

Disassembly of section .text:

87f00000 <_start>:
87f00000:	ea000014 	b	87f00058 <reset>
87f00004:	e59ff014 	ldr	pc, [pc, #20]	; 87f00020<_end+0xfffe07c4>
87f00008:	e59ff014 	ldr	pc, [pc, #20]	; 87f00024<_end+0xfffe07c8>
87f0000c:	e59ff014 	ldr	pc, [pc, #20]	; 87f00028<_end+0xfffe07cc>
87f00010:	e59ff014 	ldr	pc, [pc, #20]	; 87f0002c<_end+0xfffe07d0>
87f00014:	e59ff014 	ldr	pc, [pc, #20]	; 87f00030<_end+0xfffe07d4>
87f00018:	e59ff014 	ldr	pc, [pc, #20]	; 87f00034<_end+0xfffe07d8>
87f0001c:	e59ff014 	ldr	pc, [pc, #20]	; 87f00038<_end+0xfffe07dc>

87f00020 <_undefined_instruction>:
87f00020:	87f14a20 	.word	0x87f14a20

87f00024 <_software_interrupt>:
87f00024:	87f14a80 	.word	0x87f14a80

87f00028 <_prefetch_abort>:
87f00028:	87f14ae0 	.word	0x87f14ae0

87f0002c <_data_abort>:
87f0002c:	87f14b40 	.word	0x87f14b40

87f00030 <_not_used>:
87f00030:	87f14ba0 	.word	0x87f14ba0

87f00034 <_irq>:
87f00034:	87f14c00 	.word	0x87f14c00

87f00038 <_fiq>:
87f00038:	87f14c60 	.word	0x87f14c60
87f0003c:	deadbeef 	.word	0xdeadbeef

87f00040 <_barebox_start>:
87f00040:	87f00000 	.word	0x87f00000

87f00044 <_bss_start>:
87f00044:	87f1a908 	.word	0x87f1a908

87f00048 <_bss_end>:
87f00048:	87f1f85c 	.word	0x87f1f85c

87f0004c <_TEXT_BASE>:
87f0004c:	87f00000 	.word	0x87f00000

87f00050 <_MALLOC_BASE>:
87f00050:	87b00000 	.word	0x87b00000

(With 87fxxxx replaced with 0570xxxx of course)

Since EP93xx is not in mainline maybe you can provide us your patches
and I think we should be able to help you.


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