path: root/baremetal/313index-bounds-check.subx

# Helper to check an array's bounds, and to abort if they're violated.
# Really only intended to be called from code generated by mu.subx.

== code

__check-mu-array-bounds:  # index: int, elem-size: int, arr-size: int, function-name: (addr array byte), array-name: (addr array byte)
    # . prologue
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    50/push-eax
    51/push-ecx
    52/push-edx
    # . not bothering saving ebx; it's only clobbered if we're going to abort
    # ecx = arr-size
    8b/-> *(ebp+0x10) 1/r32/ecx
    # var overflow/edx: int = 0
    ba/copy-to-edx 0/imm32
    # var offset/eax: int = index * elem-size
    8b/-> *(ebp+8) 0/r32/eax
    f7 4/subop/multiply-eax-with *(ebp+0xc)
    # check for overflow
    81 7/subop/compare %edx 0/imm32
    0f 85/jump-if-!= __check-mu-array-bounds:overflow/disp32
    # check bounds
    39/compare %eax 1/r32/ecx
    0f 82/jump-if-unsigned< $__check-mu-array-bounds:end/disp32  # negative index should always abort
    # abort if necessary
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "fn " 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 *(ebp+0x14) 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 ": offset " 3)  # 3=cyan
    (draw-int32-hex-wrapping-right-then-down-from-cursor-over-full-screen 0 %eax 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 " is too large for array '" 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 *(ebp+0x18) 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "'" 3)  # 3=cyan
    {
      eb/jump loop/disp8
    }
    # never gets here
$__check-mu-array-bounds:end:
    # . restore registers
    5a/pop-to-edx
    59/pop-to-ecx
    58/pop-to-eax
    # . epilogue
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return

__check-mu-array-bounds:overflow:
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "fn " 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 *(ebp+0x14) 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 ": offset to array '" 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "offset to array overflowed 32 bits" 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 *(ebp+0x18) 3)  # 3=cyan
    (draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0 "' overflowed 32 bits" 3)  # 3=cyan
    {
      eb/jump loop/disp8
    }
    # never gets here