61 lines
2.5 KiB
Plaintext
61 lines
2.5 KiB
Plaintext
# Example reading commandline arguments: compute length of first arg.
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#
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# To run:
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# $ bootstrap/bootstrap translate ex8.subx -o ex8
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# $ bootstrap/bootstrap run ex8 abc de fghi
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# Expected result:
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# $ echo $?
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# 3 # length of 'abc'
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#
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# At the start of a SubX program:
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# argc: *esp
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# argv[0]: *(esp+4)
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# argv[1]: *(esp+8)
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# ...
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# Locals start from esp-4 downwards.
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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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Entry:
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# . prologue
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89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
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# eax = ascii-length(argv[1])
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# . . push args
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ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8)
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# . . call
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e8/call ascii-length/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
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# exit(eax)
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89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
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e8/call syscall_exit/disp32
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ascii-length: # s: (addr array byte) -> n/eax
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# edx = s
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8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 2/r32/edx 4/disp8 . # copy *(esp+4) to edx
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# var result/eax = 0
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b8/copy-to-eax 0/imm32
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$ascii-length:loop:
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# var c/ecx = *s
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8a/copy-byte 0/mod/* 2/rm32/edx . . . 1/r32/CL . . # copy byte at *edx to CL
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# if (c == '\0') break
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81 7/subop/compare 3/mod/direct 1/rm32/ecx . . . . . 0/imm32/null # compare ecx
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74/jump-if-= $ascii-length:end/disp8
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# ++s
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42/increment-edx
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# ++result
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40/increment-eax
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# loop
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eb/jump $ascii-length:loop/disp8
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$ascii-length:end:
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# return eax
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c3/return
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== data
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# . . vim:nowrap:textwidth=0
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