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# 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
(write-buffered Stderr "fn ")
(write-buffered Stderr *(ebp+0x14))
(write-buffered Stderr ": offset ")
(write-int32-hex-buffered Stderr %eax)
(write-buffered Stderr " is too large for array '")
(write-buffered Stderr *(ebp+0x18))
(write-buffered Stderr "'\n")
(flush Stderr)
# exit(1)
bb/copy-to-ebx 1/imm32
e8/call syscall_exit/disp32
# 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:
# "fn " function-name ": offset to array '" array-name "' overflowed 32 bits\n"
(write-buffered Stderr "fn ")
(write-buffered Stderr *(ebp+0x14))
(write-buffered Stderr ": offset to array '")
(write-buffered Stderr *(ebp+0x18))
(write-buffered Stderr "' overflowed 32 bits\n")
(flush Stderr)
# exit(1)
bb/copy-to-ebx 1/imm32
e8/call syscall_exit/disp32
# never gets here
# potential alternative
#? __bounds-check: # msg: (addr array byte)
#? (write-buffered Stderr "abort: array bounds exceeded in fn ")
#? 8b/-> *(esp+4) 0/r32/eax # we're going to abort, so just clobber away
#? (write-buffered Stderr %eax)
#? (write-buffered Stderr Newline)
#? # exit(1)
#? bb/copy-to-ebx 1/imm32
#? e8/call syscall_exit/disp32
# to be called as follows:
# var/reg <- index arr/rega: (addr array T), idx/regi: int
# | if size-of(T) is 1, 2, 4 or 8
# => # temporarily save array size to reg to check bounds
# "8b/-> *" rega " " reg "/r32"
# "c1/shift 5/subop/right %" reg " " log2(size-of(T)) "/imm32"
# "3b/compare " reg "/r32 *" rega
# "68/push \"" function "\"/imm32" # pass function name to error message
# "0f 8d/jump-if->= __bounds_check/disp32"
# "81 0/subop/add %esp 4/imm32" # drop function name
# # actually save the index addr in reg
# "8d/copy-address *(" rega "+" regi "<<" log2(size-of(T)) "+4) " reg "/r32"
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