diff options
Diffstat (limited to 'linux/apps/ex8.subx')
| -rw-r--r-- | linux/apps/ex8.subx | 60 |
1 files changed, 60 insertions, 0 deletions
diff --git a/linux/apps/ex8.subx b/linux/apps/ex8.subx new file mode 100644 index 00000000..2d962be4 --- /dev/null +++ b/linux/apps/ex8.subx @@ -0,0 +1,60 @@ +# Example reading commandline arguments: compute length of first arg. +# +# To run: +# $ bootstrap/bootstrap translate apps/ex8.subx -o ex8 +# $ bootstrap/bootstrap run ex8 abc de fghi +# Expected result: +# $ echo $? +# 3 # length of 'abc' +# +# At the start of a SubX program: +# argc: *esp +# argv[0]: *(esp+4) +# argv[1]: *(esp+8) +# ... +# Locals start from esp-4 downwards. + +== code +# instruction effective address register displacement immediate +# . op subop mod rm32 base index scale r32 +# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes + +Entry: + # . prologue + 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp + # eax = ascii-length(argv[1]) + # . . push args + ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8) + # . . call + e8/call ascii-length/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + + # exit(eax) + 89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx + e8/call syscall_exit/disp32 + +ascii-length: # s: (addr array byte) -> n/eax + # edx = s + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 2/r32/edx 4/disp8 . # copy *(esp+4) to edx + # var result/eax = 0 + b8/copy-to-eax 0/imm32 +$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 |