46 lines
2.2 KiB
Plaintext
46 lines
2.2 KiB
Plaintext
# _write: write to a file descriptor
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== code
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# instruction effective address operand 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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# main:
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# syscall(exit, 0) -- can't test _write just yet
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bb/copy-to-EBX 0/imm32
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b8/copy-to-EAX 1/imm32
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cd/syscall 0x80/imm8
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_write: # fd : int, s : (address array byte) -> <void>
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# prolog
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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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53/push-EBX
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# syscall(write, fd, (data) s+4, (size) *s)
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# fd : EBX
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8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 3/r32/EBX 8/disp8 . # copy *(EBP+8) to EBX
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# data : ECX = s+4
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8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 1/r32/ECX 0xc/disp8 . # copy *(EBP+12) to ECX
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81 0/subop/add 3/mod/direct 1/rm32/ECX . . . . . 4/imm32 # add to ECX
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# size : EDX = *s
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8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 2/r32/EDX 0xc/disp8 . # copy *(EBP+12) to EDX
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8b/copy 0/mod/indirect 2/rm32/EDX . . . 2/r32/EDX . . # copy *EDX to EDX
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# syscall
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b8/copy-to-EAX 4/imm32/write
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cd/syscall 0x80/imm8
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# restore registers
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5b/pop-to-EBX
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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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# epilog
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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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