why do we need reloc_offset ??

[HongWoo Lee]

Hi everyone~

In ther linux kernel code, I found the reloc_offset.

{{{
// file : misc.S
/* Returns (address we are running at) - (address we were linked at)
 * for use before the text and data are mapped to KERNELBASE.
 */
_GLOBAL(reloc_offset)
}}}

I couldn't understand the comment saying "Returns (address we are running
at) - (address we were linked at)".
For now, I'm studying each instruction.

And below is best comment I can explain for each instruction.

_GLOBAL(reloc_offset)
        mflr    r0                // move from link register, save the
return address
        bl      1f                 // bl 1f
1:     mflr    r3                // move from link register, r3 is just
return address pointing itself
        LOAD_REG_IMMEDIATE(r4,1b)    // get the 1b address, r4 is the
address
        subf    r3,r4,r3        // r3 = r3 – r4
        mtlr    r0                // restore return address
        blr

After this, I still don't know why "r3-r4" is the offset.
And what does it mean ??

Please explain to me the reason why we need reloc_offset and the code.
Or let me know any helpful reference about this.

Thank in advance.

HongWoo.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ozlabs.org/pipermail/linuxppc-dev/attachments/20090902/6a65c6f4/attachment.htm>