[U-Boot] Relocation confusion

[Drasko DRASKOVIC]

Hi all,
I have some questions regarding start.S code for arm926ejs. Looking at the
relocation code of u-boot:

relocate:                   /* relocate U-Boot to RAM        */
    adr    r0, _start            /* r0 <- current position of code   */
    ldr    r1, _TEXT_BASE        /* test if we run from flash or RAM */
    cmp     r0, r1          /* don't reloc during debug         */
    beq     stack_setup

    ldr    r2, _armboot_start
    ldr    r3, _bss_start
    sub    r2, r3, r2            /* r2 <- size of armboot            */
    add    r2, r0, r2            /* r2 <- source end address         */


1) What is exactly difference between _start and _armboot_start ? I can see
in the same file definition of _armboot_start :

.globl _armboot_start
_armboot_start:
    .word _start

So, I am confused there - it looks like they are the same thing.

2)  Line:
 sub    r2, r3, r2
is logical, but after we do :
add    r2, r0, r2      /* r2 <- source end address         */
to find source end address. But if _start and _armboot_start are the same,
we already have this source end address : it is _bss_start.

3) Based on this, if _armboot_start and _start are not the same thing, I
could guess that _start is pointing at 0x0 of the flash (or SDRAM), i.e. it
is uP entry point after reset, and _armboot_start is the place where we
start to put u-boot instructions (TEXT section). That would mean that we
either have
a) some program uP will execute before u-boot. What could that ever be?
b) some section of u-boot that goes before TEXT section, and will never be
relocated to RAM _TEXT_BASE. What could that ever be?

Thanks for your answers.

Best regards,
Drasko DRASKOVIC