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# Example reading commandline arguments: compute length of first arg.
#
# To run:
# $ ./translate_subx 000init.subx apps/ex8.subx
# $ ./a.elf abc de fghi
# Expected result:
# $ echo $?
# 3 # length of 'abc'
#
# At the start of a SubX program:
# argc: *esp
# argv[0]: *(esp+4)
# argv[1]: *(esp+8)
# ...
# Locals start from esp-4 downwards.
== code
# instruction effective address register displacement immediate
# . op subop mod rm32 base index scale r32
# . 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
Entry:
# . prologue
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# eax = ascii-length(argv[1])
# . . push args
ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8)
# . . call
e8/call ascii-length/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# exit(eax)
89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
e8/call syscall_exit/disp32
ascii-length: # s: (addr array byte) -> n/eax
# edx = s
8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 2/r32/edx 4/disp8 . # copy *(esp+4) to edx
# var result/eax = 0
b8/copy-to-eax 0/imm32
$ascii-length:loop:
# var c/ecx = *s
8a/copy-byte 0/mod/* 2/rm32/edx . . . 1/r32/CL . . # copy byte at *edx to CL
# if (c == '\0') break
81 7/subop/compare 3/mod/direct 1/rm32/ecx . . . . . 0/imm32/null # compare ecx
74/jump-if-= $ascii-length:end/disp8
# ++s
42/increment-edx
# ++result
40/increment-eax
# loop
eb/jump $ascii-length:loop/disp8
$ascii-length:end:
# return eax
c3/return
== data
# . . vim:nowrap:textwidth=0
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