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Diffstat (limited to 'apps/ex9.subx')
| -rw-r--r-- | apps/ex9.subx | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/apps/ex9.subx b/apps/ex9.subx new file mode 100644 index 00000000..443e443e --- /dev/null +++ b/apps/ex9.subx @@ -0,0 +1,52 @@ +# Example showing arg order on the stack. +# +# Show difference between ascii codes of first letter of first arg and first +# letter of second arg. +# +# To run: +# $ ./subx translate init.linux examples/ex9.subx -o examples/ex9 +# $ ./subx run examples/ex9 z x +# Expected result: +# $ echo $? +# 2 +# +# 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 + # ascii-difference(argv[1], argv[2]) + # . . push argv[2] + ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12) + # . . push argv[1] + ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8) + # . . call + e8/call ascii-difference/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/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-difference: # (s1, s2) : null-terminated ascii strings + # a = first letter of s1 (ecx) + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none 0/r32/eax 4/disp8 . # copy *(esp+4) to eax + 8b/copy 0/mod/indirect 0/rm32/eax . . . 0/r32/eax . . # copy *eax to eax + # b = first letter of s2 (edx) + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none 1/r32/ecx 8/disp8 # copy *(esp+8) to ecx + 8b/copy 0/mod/indirect 1/rm32/ecx . . . 1/r32/ecx . . # copy *ecx to ecx + # a-b + 29/subtract 3/mod/direct 0/rm32/eax . . . 1/r32/ecx . . # subtract ecx from eax + c3/return + +# . . vim:nowrap:textwidth=0 |