53 lines
2.4 KiB
Plaintext
53 lines
2.4 KiB
Plaintext
# instruction effective address register displacement immediate
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# . op subop mod rm32 base index scale r32
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# . 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
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# Fill a region of memory with zeroes.
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zero-out: # start: (addr byte), size: int
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# pseudocode:
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# curr/esi = start
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# i/ecx = 0
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# while true
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# if (i >= size) break
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# *curr = 0
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# ++curr
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# ++i
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#
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# . prologue
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55/push-ebp
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89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
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# . save registers
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50/push-eax
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51/push-ecx
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52/push-edx
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56/push-esi
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# curr/esi = start
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 8/disp8 . # copy *(ebp+8) to esi
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# var i/ecx: int = 0
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31/xor 3/mod/direct 1/rm32/ecx . . . 1/r32/ecx . . # clear ecx
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# edx = size
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 2/r32/edx 0xc/disp8 . # copy *(ebp+12) to edx
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$zero-out:loop:
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# if (i >= size) break
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39/compare 3/mod/direct 1/rm32/ecx . . . 2/r32/edx . . # compare ecx with edx
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7d/jump-if->= $zero-out:end/disp8
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# *curr = 0
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c6 0/subop/copy-byte 0/mod/direct 6/rm32/esi . . . . . 0/imm8 # copy byte to *esi
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# ++curr
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46/increment-esi
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# ++i
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41/increment-ecx
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eb/jump $zero-out:loop/disp8
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$zero-out:end:
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# . restore registers
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5e/pop-to-esi
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5a/pop-to-edx
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59/pop-to-ecx
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58/pop-to-eax
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# . epilogue
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89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
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5d/pop-to-ebp
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c3/return
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# . . vim:nowrap:textwidth=0
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