1 # Helper to check an array's bounds, and to abort if they're violated.
  2 # Really only intended to be called from code generated by mu.subx.
  3 
  4 == code
  5 
  6 __check-mu-array-bounds:  # index: int, elem-size: int, arr-size: int, function-name: (addr array byte), array-name: (addr array byte)
  7     # . prologue
  8     55/push-ebp
  9     89/<- %ebp 4/r32/esp
 10     # . save registers
 11     50/push-eax
 12     51/push-ecx
 13     52/push-edx
 14     # . not bothering saving ebx; it's only clobbered if we're going to abort
 15     # ecx = arr-size
 16     8b/-> *(ebp+0x10) 1/r32/ecx
 17     # var overflow/edx: int = 0
 18     ba/copy-to-edx 0/imm32
 19     # var offset/eax: int = index * elem-size
 20     8b/-> *(ebp+8) 0/r32/eax
 21     f7 4/subop/multiply-eax-with *(ebp+0xc)
 22     # check for overflow
 23     81 7/subop/compare %edx 0/imm32
 24     0f 85/jump-if-!= __check-mu-array-bounds:overflow/disp32
 25     # check bounds
 26     39/compare %eax 1/r32/ecx
 27     0f 82/jump-if-unsigned< $__check-mu-array-bounds:end/disp32  # negative index should always abort
 28     # abort if necessary
 29     (write-buffered Stderr "fn ")
 30     (write-buffered Stderr *(ebp+0x14))
 31     (write-buffered Stderr ": offset ")
 32     (write-int32-hex-buffered Stderr %eax)
 33     (write-buffered Stderr " is too large for array '")
 34     (write-buffered Stderr *(ebp+0x18))
 35     (write-buffered Stderr "'\n")
 36     (flush Stderr)
 37     # exit(1)
 38     bb/copy-to-ebx 1/imm32
 39     e8/call syscall_exit/disp32
 40     # never gets here
 41 $__check-mu-array-bounds:end:
 42     # . restore registers
 43     5a/pop-to-edx
 44     59/pop-to-ecx
 45     58/pop-to-eax
 46     # . epilogue
 47     89/<- %esp 5/r32/ebp
 48     5d/pop-to-ebp
 49     c3/return
 50 
 51 __check-mu-array-bounds:overflow:
 52     # "fn " function-name ": offset to array '" array-name "' overflowed 32 bits\n"
 53     (write-buffered Stderr "fn ")
 54     (write-buffered Stderr *(ebp+0x14))
 55     (write-buffered Stderr ": offset to array '")
 56     (write-buffered Stderr *(ebp+0x18))
 57     (write-buffered Stderr "' overflowed 32 bits\n")
 58     (flush Stderr)
 59     # exit(1)
 60     bb/copy-to-ebx 1/imm32
 61     e8/call syscall_exit/disp32
 62     # never gets here
 63 
 64 # potential alternative
 65 
 66 #? __bounds-check:  # msg: (addr array byte)
 67 #?   (write-buffered Stderr "abort: array bounds exceeded in fn ")
 68 #?   8b/-> *(esp+4) 0/r32/eax  # we're going to abort, so just clobber away
 69 #?   (write-buffered Stderr %eax)
 70 #?   (write-buffered Stderr Newline)
 71 #?   # exit(1)
 72 #?   bb/copy-to-ebx 1/imm32
 73 #?   e8/call syscall_exit/disp32
 74 
 75 # to be called as follows:
 76 #   var/reg <- index arr/rega: (addr array T), idx/regi: int
 77 #     | if size-of(T) is 1, 2, 4 or 8
 78 #         => # temporarily save array size to reg to check bounds
 79 #            "8b/-> *" rega " " reg "/r32"
 80 #            "c1/shift 5/subop/right %" reg " " log2(size-of(T)) "/imm32"
 81 #            "3b/compare " reg "/r32 *" rega
 82 #            "68/push \"" function "\"/imm32"  # pass function name to error message
 83 #            "0f 8d/jump-if->= __bounds_check/disp32"
 84 #            "81 0/subop/add %esp 4/imm32"  # drop function name
 85 #            # actually save the index addr in reg
 86 #            "8d/copy-address *(" rega "+" regi "<<" log2(size-of(T)) "+4) " reg "/r32"
 87 
 88 __mu-abort-null-index-base-address:
 89     (write-buffered Stderr "null address in 'index'\n")
 90     (flush Stderr)
 91     # exit(1)
 92     bb/copy-to-ebx 1/imm32
 93     e8/call syscall_exit/disp32
 94     # never gets here
 95 
 96 __mu-abort-null-get-base-address:
 97     (write-buffered Stderr "null address in 'get'\n")
 98     (flush Stderr)
 99     # exit(1)
100     bb/copy-to-ebx 1/imm32
101     e8/call syscall_exit/disp32
102     # never gets here