abt kernel 2.6 compressed/head.s

[zyxsjl]

 hi anyone, 
I have not understood some code in this file below: 
    #ifndef CONFIG_ZBOOT_ROM
  /*
* If we're running fully PIC === CONFIG_ZBOOT_ROM = n,
* we need to fix up pointers into the BSS region.
  * r2 - BSS start
  * r3 - BSS end
  * sp - stack pointer
  */
  add r2, r2, r0
  add r3, r3, r0
  add sp, sp, r0
  /*
  * Relocate all entries in the GOT table.
  */
1: ldr r1, [r6, #0] @ relocate entries in the GOT
add r1, r1, r0 @ table. This fixes up the
  str r1, [r6], #4 @ C references.
  cmp r6, ip
  blo 1b
#else
  /*
* Relocate entries in the GOT table. We only relocate
* the entries that are outside the (relocated) BSS region.
  */
1: ldr r1, [r6, #0] @ relocate entries in the GOT
  cmp r1, r2 @ entry < bss_start ||
  cmphs r3, r1   @ _end < entry
addlo r1, r1, r0 @ table. This fixes up the
  str r1, [r6], #4 @ C references.
  cmp r6, ip
  blo 1b
#endif
my question is:what is the different between the both CONFIG_ZBOOT_ROM=y or n, and so led to the different tackles from the above code on relocation?
 thanks ahead
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