48 lines
3.2 KiB
Plaintext
48 lines
3.2 KiB
Plaintext
## read a character from stdin, save it to a local on the stack, write it to stdout
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#
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# To run:
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# $ subx translate ex5.subx ex5
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# $ subx run ex5
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== 0x08048054 # code segment, after leaving room for ELF header and segment headers
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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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## function main
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# prolog
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55/push # 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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# allocate x on the stack
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81 5/subop/subtract 3/mod/direct 4/rm32/ESP 4/imm32 # subtract 4 bytes from ESP
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## read(stdin, x, 1)
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# fd = 0 (stdin)
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bb/copy 0/imm32 # copy 0 to EBX
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# set location to read character to
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89/copy 3/mod/direct 1/rm32/ECX 5/r32/EBP # copy EBP to ECX
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# size = 1 character
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ba/copy 1/imm32 # copy 1 to EDX
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# syscall = read
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b8/copy 3/imm32 # copy 3 to EAX
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# call
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cd/syscall 0x80/imm8 # int 80h
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## write(stdout, x, 1)
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# fd = 1 (stdout)
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bb/copy 1/imm32 # copy 1 to EBX
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# set location of character to write out
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89/copy 3/mod/direct 1/rm32/ECX 5/r32/EBP # copy EBP to ECX
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# size = 1 character
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ba/copy 1/imm32 # copy 1 to EDX
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# syscall = write
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b8/copy 4/imm32 # copy 4 to EAX
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# call
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cd/syscall 0x80/imm8 # int 80h
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## exit(EBX)
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b8/copy 1/imm32 # copy 1 to EAX
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cd/syscall 0x80/imm8 # int 80h
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# vim:ft=subx:nowrap
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