diff options
Diffstat (limited to 'examples/ex8.subx')
| -rw-r--r-- | examples/ex8.subx | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/examples/ex8.subx b/examples/ex8.subx new file mode 100644 index 00000000..9d7255e1 --- /dev/null +++ b/examples/ex8.subx @@ -0,0 +1,61 @@ +# Example reading commandline arguments: compute length of first arg. +# +# To run (from the subx directory): +# $ ./subx translate examples/ex8.subx -o examples/ex8 +# $ ./subx run examples/ex8 abc de fghi +# Expected result: +# $ echo $? +# 3 # length of 'abc' +# +# At the start of a SubX program: +# argc: *ESP +# argv[0]: *(ESP+4) +# argv[1]: *(ESP+8) +# ... +# Locals start from ESP-4 downwards. + +== code 0x09000000 +# instruction effective address register displacement immediate +# . op subop mod rm32 base index scale r32 +# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes + +Entry: + # . prolog + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # EAX = ascii-length(argv[1]) + # . . push args + ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 8/disp8 . # push *(EBP+8) + # . . call + e8/call ascii-length/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP + + # exit(EAX) + 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX + b8/copy-to-EAX 1/imm32/exit + cd/syscall 0x80/imm8 + +ascii-length: # s : (address array byte) -> n/EAX + # EDX = s + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 2/r32/EDX 4/disp8 . # copy *(ESP+4) to EDX + # var result/EAX = 0 + b8/copy-to-EAX 0/imm32 +$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 # compare ECX + 74/jump-if-equal $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 0x0a000000 + +# . . vim:nowrap:textwidth=0 |