A Merry Christmas Greeting, in ARM64 (AArch64) Asm

festive.s

; festive.s - Christmas tree in memory dump
; Assemble: as -o festive.o festive.s
; Link:     ld -o festive festive.o -l System -syslibroot `xcrun -sdk macosx --show-sdk-path` -e _main
;
; Created by Kush S.
;
; Read more: https://skushagra.com/posts/2025-12-25-aarch64-christmas/
;
; === BASIC WORKFLOW (tree in memory dump) ===
;   lldb festive
;   (lldb) b done
;   (lldb) r
;   (lldb) memory read $x20 $x20+160
;
; === CURSES GUI STORYTELLING MODE ===
;   lldb festive
;   (lldb) b main              # Start of the show
;   (lldb) b star              # Watch the star appear
;   (lldb) b tree              # Tree takes shape  
;   (lldb) b trunk             # Trunk grows
;   (lldb) b message           # The greeting appears
;   (lldb) b done              # Grand finale
;   (lldb) r
;   (lldb) gui
;   - Press 'c' to continue to each breakpoint
;   - Watch the code flow through each "act"
;   - At 'done': press Esc, then type:
;       memory read $x20 $x20+160
;       register read x0 x1 x2 x3 x4 x5 x6 x7
;   - Screenshot the tree + festive registers!

.global _main
.align 4

.data
canvas: .space 256

.text
_main:
    adrp x20, canvas@PAGE
    add x20, x20, canvas@PAGEOFF

star:
    ; Each row is 16 bytes = one line in memory dump
    ; The ASCII column on the right will show our art

    ; Row 0: "      *         " (16 chars, star centered)
    mov w0, #0x2020
    strh w0, [x20, #0]
    strh w0, [x20, #2]
    strh w0, [x20, #4]
    mov w0, #0x2A               ; *
    strb w0, [x20, #6]
    mov w0, #0x2020
    strh w0, [x20, #7]
    strh w0, [x20, #9]
    strh w0, [x20, #11]
    strh w0, [x20, #13]
    mov w0, #0x20
    strb w0, [x20, #15]

tree:
    ; Row 1: "     /|\        "
    mov w0, #0x2020
    strh w0, [x20, #16]
    strh w0, [x20, #18]
    mov w0, #0x20
    strb w0, [x20, #20]
    mov w0, #0x2F               ; /
    strb w0, [x20, #21]
    mov w0, #0x7C               ; |
    strb w0, [x20, #22]
    mov w0, #0x5C               ; backslash
    strb w0, [x20, #23]
    mov w0, #0x2020
    strh w0, [x20, #24]
    strh w0, [x20, #26]
    strh w0, [x20, #28]
    strh w0, [x20, #30]

    ; Row 2: "    /|||\       "
    mov w0, #0x2020
    strh w0, [x20, #32]
    strh w0, [x20, #34]
    mov w0, #0x2F               ; /
    strb w0, [x20, #36]
    mov w0, #0x7C               ; |
    strb w0, [x20, #37]
    strb w0, [x20, #38]
    strb w0, [x20, #39]
    mov w0, #0x5C               ; backslash
    strb w0, [x20, #40]
    mov w0, #0x2020
    strh w0, [x20, #41]
    strh w0, [x20, #43]
    strh w0, [x20, #45]
    mov w0, #0x20
    strb w0, [x20, #47]

    ; Row 3: "   /|||||\      "
    mov w0, #0x2020
    strh w0, [x20, #48]
    mov w0, #0x20
    strb w0, [x20, #50]
    mov w0, #0x2F               ; /
    strb w0, [x20, #51]
    mov w0, #0x7C               ; |
    strb w0, [x20, #52]
    strb w0, [x20, #53]
    strb w0, [x20, #54]
    strb w0, [x20, #55]
    strb w0, [x20, #56]
    mov w0, #0x5C               ; backslash
    strb w0, [x20, #57]
    mov w0, #0x2020
    strh w0, [x20, #58]
    strh w0, [x20, #60]
    strh w0, [x20, #62]

    ; Row 4: "  /|||||||\     "
    mov w0, #0x2020
    strh w0, [x20, #64]
    mov w0, #0x2F               ; /
    strb w0, [x20, #66]
    mov w0, #0x7C               ; |
    strb w0, [x20, #67]
    strb w0, [x20, #68]
    strb w0, [x20, #69]
    strb w0, [x20, #70]
    strb w0, [x20, #71]
    strb w0, [x20, #72]
    strb w0, [x20, #73]
    mov w0, #0x5C               ; backslash
    strb w0, [x20, #74]
    mov w0, #0x2020
    strh w0, [x20, #75]
    strh w0, [x20, #77]
    mov w0, #0x20
    strb w0, [x20, #79]

trunk:
    ; Row 5: "      |         " (trunk)
    mov w0, #0x2020
    strh w0, [x20, #80]
    strh w0, [x20, #82]
    strh w0, [x20, #84]
    mov w0, #0x7C               ; |
    strb w0, [x20, #86]
    mov w0, #0x2020
    strh w0, [x20, #87]
    strh w0, [x20, #89]
    strh w0, [x20, #91]
    strh w0, [x20, #93]
    mov w0, #0x20
    strb w0, [x20, #95]

    ; Row 6: "     |||        " (trunk base)
    mov w0, #0x2020
    strh w0, [x20, #96]
    strh w0, [x20, #98]
    mov w0, #0x20
    strb w0, [x20, #100]
    mov w0, #0x7C               ; |
    strb w0, [x20, #101]
    strb w0, [x20, #102]
    strb w0, [x20, #103]
    mov w0, #0x2020
    strh w0, [x20, #104]
    strh w0, [x20, #106]
    strh w0, [x20, #108]
    strh w0, [x20, #110]

    ; Row 7: "                " (blank)
    mov w0, #0x2020
    strh w0, [x20, #112]
    strh w0, [x20, #114]
    strh w0, [x20, #116]
    strh w0, [x20, #118]
    strh w0, [x20, #120]
    strh w0, [x20, #122]
    strh w0, [x20, #124]
    strh w0, [x20, #126]

message:
    ; Row 8: " MERRY CHRISTMAS" (16 chars exactly)
    mov w0, #0x20
    strb w0, [x20, #128]
    mov w0, #0x4D               ; M
    strb w0, [x20, #129]
    mov w0, #0x45               ; E
    strb w0, [x20, #130]
    mov w0, #0x52               ; R
    strb w0, [x20, #131]
    strb w0, [x20, #132]
    mov w0, #0x59               ; Y
    strb w0, [x20, #133]
    mov w0, #0x20
    strb w0, [x20, #134]
    mov w0, #0x43               ; C
    strb w0, [x20, #135]
    mov w0, #0x48               ; H
    strb w0, [x20, #136]
    mov w0, #0x52               ; R
    strb w0, [x20, #137]
    mov w0, #0x49               ; I
    strb w0, [x20, #138]
    mov w0, #0x53               ; S
    strb w0, [x20, #139]
    mov w0, #0x54               ; T
    strb w0, [x20, #140]
    mov w0, #0x4D               ; M
    strb w0, [x20, #141]
    mov w0, #0x41               ; A
    strb w0, [x20, #142]
    mov w0, #0x53               ; S
    strb w0, [x20, #143]

    ; Row 9: "   DEC 25 2025  "
    mov w0, #0x2020
    strh w0, [x20, #144]
    mov w0, #0x20
    strb w0, [x20, #146]
    mov w0, #0x44               ; D
    strb w0, [x20, #147]
    mov w0, #0x45               ; E
    strb w0, [x20, #148]
    mov w0, #0x43               ; C
    strb w0, [x20, #149]
    mov w0, #0x20
    strb w0, [x20, #150]
    mov w0, #0x32               ; 2
    strb w0, [x20, #151]
    mov w0, #0x35               ; 5
    strb w0, [x20, #152]
    mov w0, #0x20
    strb w0, [x20, #153]
    mov w0, #0x32               ; 2
    strb w0, [x20, #154]
    mov w0, #0x30               ; 0
    strb w0, [x20, #155]
    mov w0, #0x32               ; 2
    strb w0, [x20, #156]
    mov w0, #0x35               ; 5
    strb w0, [x20, #157]
    mov w0, #0x2020
    strh w0, [x20, #158]

    ; Festive registers for bonus screenshot
    mov x0, #0xDEC
    mov x1, #0x25
    mov x2, #0x2025
    mov x3, #0xCAFE
    mov x4, #0xF00D
    mov x5, #0xBEEF
    mov x6, #0x1CE
    mov x7, #0xC01D

done:
    mov x0, #0
    mov x16, #1
    svc #0x80