43 lines
1.8 KiB
Plaintext
43 lines
1.8 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 (from the subx directory):
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# $ subx translate examples/ex5.subx -o examples/ex5
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# $ subx run examples/ex5
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== code
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# 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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# main:
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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 from ESP
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# syscall(read, stdin, x, 1)
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# . fd = 0 (stdin)
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bb/copy-to-EBX 0/imm32
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# . data = x (location to write result to)
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8d/copy-address 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 1/r32/ECX 4/disp8 . # copy ESP+4 to ECX
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# . size = 1 character
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ba/copy-to-EDX 1/imm32
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# . syscall
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b8/copy-to-EAX 3/imm32/read
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cd/syscall 0x80/imm8
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# syscall(write, stdout, x, 1)
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# . fd = 1 (stdout)
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bb/copy-to-EBX 1/imm32
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# . data = x (location to read from)
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8d/copy-address 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 1/r32/ECX 4/disp8 . # copy ESP+4 to ECX
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# . size = 1 character
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ba/copy-to-EDX 1/imm32
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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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# syscall(exit, EBX)
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b8/copy-to-EAX 1/imm32/exit
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cd/syscall 0x80/imm8
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# . . vim:nowrap:textwidth=0
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