Coto: IRQ Handler ROP routine .Hooks RealView ARM into GNUC

@this is Coto's IRQ driver that hooks compiled machine code from RealView into GNU-C ARM Compiler.
@------------------------------------------------------------------------------------------------------
@(this is definitely from coto's asm)

.align 4
.code 32
.arm
.cpu arm7tdmi
.text

@patches (from 20/02/15 outdated)
@ldr #imm -4095 and +4095 (inclusive). / remember pc is 8 bytes ahead (prefetch + next opcode)
.global dummyopcode
dummyopcode:
    ldr pc,[pc, #(-(0x204+0x8)+(0x000000d0))]       @replace 0x204 with current PC address + offset (word size) of the word location on rom (must be 4095+- from base)
    ldr pc,[pc,#-0x4]
    bx r1
    pop  {r0,r2,r4,r5,r14}

.global PATCH_ENTRYPOINT
.type   PATCH_ENTRYPOINT STT_FUNC
PATCH_ENTRYPOINT:
    @bootrom opcode entrypoint
    .word 0xe51ff13c    @ldr pc,[pc,#0x4] opcode 1/2/ should be installed @ rom entrypoint
    .word 0x08ff8000    @value 2/2 (PATCH_BOOTCODE) / should be installed @ rom_start+0xd0
    @IRQ handler entrypoint

    .word 0xe51ff004    @IRQ handler + 0 ARM opcode (to replace with ldr pc,=0x08FE0000)
    .word 0x08FE0000    @0x08FE0000 from PC (where you want to load this word)

@entrypoint approach patcher
.global PATCH_BOOTCODE
.type   PATCH_BOOTCODE STT_FUNC
PATCH_BOOTCODE:
    push {r0,r1,r2,lr}                  @rd is temp
    mov r0,#((0x08000000 + 0x1000000))  @(ARM code)
    sub r0,#(0x10000)                   @PATCH_START @0x08ff0000
    mov lr,pc
    bx  r0
    pop {r0,r1,r2,lr}

    mov r0,#0xe3000000      @/
    orr r0,#0x00a00000      @|replace with entrypoint value here
    orr r0,#0x00000012      @\

    //mov r1,#0xe5000000        @/@0xe51ff138
    //orr r1,#0x001f0000        @|replace with opcode ldr pc,[label] (LR or entrypoint address +0x4 ) here
    //orr r1,#0x0000f100
    //orr r1,#0x00000038

    mov r1,#0x08000000      @assemble 0x08000208 into r1
    orr r1,#0x00000208

    mov r2,#0xe1000000      @create ARM opcode that bx r1 (exit! from installer)
    orr r2,#0x002f0000
    orr r2,#0x0000ff00
    orr r2,#0x00000011

    stmdb r13!,{r0,r2}      @jump to stack
    mov pc, r13

@installs re-entrant IRQ routine variables
@must be installed after filling stack target (0x03001c00) content
.global PATCH_START
.type   PATCH_START STT_FUNC
PATCH_START:
    mov r1,#(0x03000000)        @\ 0x03007ffc -> 0x03001c00 (irq handler is fetched from 0x08000240) (ARM mode)
    orr r1,#0x00001b00
    orr r1,#0x000000fc

    mov r2,#((0x08000000 + 0x1000000))  @(ARM code)
    sub r2,#(0x20000)                   @PATCH_HOOK_START @0x08FE0000

    str r2,[r1]

    bx lr

.global PATCH_HOOK_START
.type   PATCH_HOOK_START STT_FUNC
PATCH_HOOK_START:
    push  {r0,r2,r4,r5,r14}

        //do any_cback here
        mov r0,#0x08000000      @NDS7_RTC_PROCESS
        orr r0,#0x00fe0000
        orr r0,#0x00008000

        mov lr,pc
        bx r0

    @(SP from wram stores)
    mov r3,#0x03000000          @save on IRQ stack: ((0x03007fff-0x200))
    orr r3,#0x00008000
    add r3,r3,#-((0x100)+(4*16))    @use irq stack reserving at least 16 opcodes

    mov r0,#0xe3000000          @0x03001c00: create ARM opcode that mov r3,0x4000000 //irq code
    orr r0,#0x00a00000
    orr r0,#0x00003300
    orr r0,#0x00000001

    mov r2,#0xe2000000          @0x03001c00: create ARM opcode that add r3,r3,0x200 //irq code
    orr r2,#0x00830000
    orr r2,#0x00003c00
    orr r2,#0x00000002

    mov r1,#(0x03000000)        @\build: 0x03007ffc -> 0x03001c08 (irq stack hook end) (ARM mode)
    orr r1,#0x2000
    sub r1,#0x3f8

    mov r4,#0xe8000000          @create ARM opcode  pop {r0,r2,r4,r5,r14} from here
    orr r4,#0x00bd0000
    orr r4,#0x00004000
    orr r4,#0x00000035

    mov r5,#0xe1000000          @create ARM opcode that bx r1 (exit! from installer)
    orr r5,#0x002f0000
    orr r5,#0x0000ff00
    orr r5,#0x00000011

    stmdb r3!,{r0,r2,r4,r5}         @jump to stack redirect /old stack cont doesnt matter
    mov pc, r3

@OUR NDS7/GBA ARM7TDMI vblank IRQ hook process.. write what you need here
.global NDS7_RTC_PROCESS
NDS7_RTC_PROCESS:

    @entry: save on IRQ stack: ((0x03007fff-0x200))
    mov r0,#0x03000000
    orr r0,#0x00008000
    add r0,r0,#-((0x100)+(4*16)+(4*16))
    stmdb r0,{r1-r14}

    @1 / n : test if PSRAM is RO or RW

    @user code init
    mov r0,#0
    mov r1,#0
    mov r2,#0
    mov r3,#0
    mov r4,#0
    mov r5,#0
    mov r6,#0
    mov r7,#0
    mov r8,#0
    mov r9,#0
    mov r10,#0
    mov r11,#0
    mov r12,#0
    mov r13,#0
    mov r14,#0

    @user code end

    @leave:save on IRQ stack: ((0x03007fff-0x200))
    mov r0,#0x03000000
    orr r0,#0x00008000
    add r0,r0,#-((0x100)+(4*16)+(4*16))
    ldmdb r0,{r1-r14}

    bx lr
.align
.pool
.end