85 lines
3.9 KiB
Plaintext
85 lines
3.9 KiB
Plaintext
|
# Fill a region of memory with zeroes.
|
||
|
|
||
|
== code
|
||
|
# instruction effective address register displacement immediate
|
||
|
# . op subop mod rm32 base index scale r32
|
||
|
# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
|
||
|
|
||
|
zero-out: # start : address, len : int
|
||
|
# pseudocode:
|
||
|
# curr/ESI = start
|
||
|
# i/ECX = 0
|
||
|
# while true
|
||
|
# if (i >= len) break
|
||
|
# *curr = 0
|
||
|
# ++curr
|
||
|
# ++i
|
||
|
#
|
||
|
# . prolog
|
||
|
55/push-EBP
|
||
|
89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
|
||
|
# . save registers
|
||
|
50/push-EAX
|
||
|
51/push-ECX
|
||
|
52/push-EDX
|
||
|
56/push-ESI
|
||
|
# curr/ESI = start
|
||
|
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 6/r32/ESI 8/disp8 . # copy *(EBP+8) to ESI
|
||
|
# i/ECX = 0
|
||
|
31/xor 3/mod/direct 1/rm32/ECX . . . 1/r32/ECX . . # clear ECX
|
||
|
# EDX = len
|
||
|
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 2/r32/EDX 0xc/disp8 . # copy *(EBP+12) to EDX
|
||
|
$zero-out:loop:
|
||
|
# if (i >= len) break
|
||
|
39/compare 3/mod/direct 1/rm32/ECX . . . 2/r32/EDX . . # compare ECX with EDX
|
||
|
7d/jump-if-greater-or-equal $zero-out:end/disp8
|
||
|
# *curr = 0
|
||
|
c6 0/subop/copy 0/mod/direct 6/rm32/ESI . . . . . 0/imm8 # copy byte to *ESI
|
||
|
# ++curr
|
||
|
46/increment-ESI
|
||
|
# ++i
|
||
|
41/increment-ECX
|
||
|
eb/jump $zero-out:loop/disp8
|
||
|
$zero-out:end:
|
||
|
# . restore registers
|
||
|
5e/pop-to-ESI
|
||
|
5a/pop-to-EDX
|
||
|
59/pop-to-ECX
|
||
|
58/pop-to-EAX
|
||
|
# . epilog
|
||
|
89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
|
||
|
5d/pop-to-EBP
|
||
|
c3/return
|
||
|
|
||
|
test-zero-out:
|
||
|
# . prolog
|
||
|
55/push-EBP
|
||
|
89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
|
||
|
# region/ECX = 34, 35, 36, 37
|
||
|
68/push 0x37363534/imm32
|
||
|
89/copy 3/mod/direct 1/rm32/ECX . . . 4/r32/ESP . . # copy ESP to ECX
|
||
|
# zero-out(ECX, 3)
|
||
|
# . . push args
|
||
|
68/push 3/imm32/len
|
||
|
51/push-ECX
|
||
|
# . . call
|
||
|
e8/call zero-out/disp32
|
||
|
# . . discard args
|
||
|
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
|
||
|
# first 3 bytes cleared, fourth left alone
|
||
|
# . check-ints-equal(*ECX, 0x37000000, msg)
|
||
|
# . . push args
|
||
|
68/push "F - test-zero-out"/imm32
|
||
|
68/push 0x37000000/imm32
|
||
|
ff 6/subop/push 0/mod/indirect 1/rm32/ECX . . . . . . # push *ECX
|
||
|
# . . call
|
||
|
e8/call check-ints-equal/disp32
|
||
|
# . . discard args
|
||
|
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
|
||
|
# . epilog
|
||
|
89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
|
||
|
5d/pop-to-EBP
|
||
|
c3/return
|
||
|
|
||
|
# . . vim:nowrap:textwidth=0
|