diff options
Diffstat (limited to 'subx/examples/ex8.subx')
| -rw-r--r-- | subx/examples/ex8.subx | 140 |
1 files changed, 51 insertions, 89 deletions
diff --git a/subx/examples/ex8.subx b/subx/examples/ex8.subx index 6f8d3979..9ea547f1 100644 --- a/subx/examples/ex8.subx +++ b/subx/examples/ex8.subx @@ -1,99 +1,61 @@ -## example showing file syscalls -# Create a file, open it for writing, write a character to it, close it, open -# it for reading, read a character from it, close it, delete it, and return -# the character read. +# Example reading commandline arguments: compute length of first arg. # # To run: -# $ subx translate ex8.subx ex8 -# $ subx run ex8 +# $ subx translate ex9.subx ex9 +# $ subx run ex9 abc de fghi # Expected result: # $ echo $? -# 97 - -== 0x08048074 # code segment, after leaving room for ELF header and segment headers +# 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. + +== 0x08048054 # code segment, after leaving room for ELF header and segment headers # instruction effective address operand 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 - - ## creat(filename) - bb/copy . . . . . . . 0x08049131/imm32/fname # copy to EBX - b9/copy . . . . . . . 0x180/imm32/fixed-perms # copy 0 to ECX - b8/copy . . . . . . . 8/imm32/creat # copy 8 to EAX - cd/syscall . . . . . . . 0x80/imm8 # int 80h - - ## fd = open(filename, O_WRONLY, 0) - bb/copy . . . . . . . 0x08049131/imm32/fname # copy to EBX - b9/copy . . . . . . . 1/imm32/wronly # copy 1 to ECX - ba/copy . . . . . . . 0x180/imm32/fixed-perms # copy 0 to EDX - b8/copy . . . . . . . 5/imm32/open # copy 5 to EAX - cd/syscall . . . . . . . 0x80/imm8 # int 80h - # save fd - bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX - 89/copy 0/mod/indirect 3/rm32/EBX 0/r32/EAX # copy EAX to *EBX - - ## write(fd, "a", 1) - # load fd - bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX - 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX - # - b9/copy . . . . . . . 0x08049129/imm32/a # copy to ECX - ba/copy . . . . . . . 1/imm32/size # copy 1 to EDX - b8/copy . . . . . . . 4/imm32/write # copy 4 to EAX - cd/syscall . . . . . . . 0x80/imm8 # int 80h - - ## close(fd) - # load fd - bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX - 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX - # - b8/copy . . . . . . . 6/imm32/close # copy 6 to EAX - cd/syscall . . . . . . . 0x80/imm8 # int 80h - - ## fd = open(filename, O_RDONLY, 0) - bb/copy . . . . . . . 0x08049131/imm32/fname # copy to EBX - b9/copy . . . . . . . 0/imm32/rdonly # copy 0 to ECX - ba/copy . . . . . . . 0x180/imm32/fixed-perms # copy 0 to EDX - b8/copy . . . . . . . 5/imm32/open # copy 5 to EAX - cd/syscall . . . . . . . 0x80/imm8 # int 80h - # save fd - bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX - 89/copy 0/mod/indirect 3/rm32/EBX 0/r32/EAX # copy EAX to *EBX - - ## read(fd, b, 1) - # load fd - bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX - 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX - # - b9/copy . . . . . . . 0x0804912d/imm32/b # copy to ECX - ba/copy . . . . . . . 1/imm32/size # copy 1 to EDX - b8/copy . . . . . . . 3/imm32/read # copy 3 to EAX - cd/syscall . . . . . . . 0x80/imm8 # int 80h - - ## close(fd) - # load fd - bb/copy . . . . . . . 0x08049125/imm32/fd # copy to EBX - 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX - # - b8/copy . . . . . . . 6/imm32/close # copy 8 to EAX - cd/syscall . . . . . . . 0x80/imm8 # int 80h - - ## unlink(filename) - bb/copy . . . . . . . 0x08049131/imm32/fname # copy to EBX - b8/copy . . . . . . . 0xa/imm32/unlink # copy 8 to EAX - cd/syscall . . . . . . . 0x80/imm8 # int 80h - - ## exit(b) - # load b - bb/copy . . . . . . . 0x0804912d/imm32/b # copy to EBX - 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX - # + # var s = argv[1] (EBX) + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 3/r32/EBX 8/disp8 . # copy *(ESP+8) to EBX + # call ascii_length(EBX) + # prepare call + 55/push . . . . . . . . # push EBP + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # push args + 53/push . . . . . . . . # push EBX + # call + e8/call . . . . . . ascii_length/disp32 + # discard args + 5a/pop . . . . . . . . # pop into EDX + # clean up after call + 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP + 5d/pop . . . . . . . . # pop to EBP + + # exit(EAX) + 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX b8/copy . . . . . . . 1/imm32/exit # copy 1 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h -== 0x08049125 # data segment -00 00 00 00 # fd -61 00 00 00 # a: string to write to file: 'a' -00 00 00 00 # b: space for string read from file -2e 66 6f 6f 00 00 00 00 # filename: '.foo' - -# vim:ft=subx:nowrap:tw& +ascii_length: # (s) + # initialize s (EDX) + 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 = 0 (EAX) + b8/copy . . . . . . . 0/imm32 # copy 1 to EAX +$al_loop: + # var c = *s (ECX) + 8a/copy 0/mod/* 2/rm32/EDX . . . 1/r32/ECX . . # copy byte at *EDX to lower byte of ECX + # if c == '\0' break + 81 7/subop/compare 3/mod/direct 1/rm32/ECX . . . . . 0/imm32 # compare ECX with 0 + 74/jump-if-zero . . . . . . . $al_ret/disp8 # jump if equal + # ++s + 81 0/subop/add 3/mod/direct 2/rm32/EDX . . . . . 1/imm32 # add 1 to EDX + # ++result + 81 0/subop/add 3/mod/direct 0/rm32/EAX . . . . . 1/imm32 # add 1 to EAX + # loop + eb/jump . . . . . . . $al_loop/disp8 # jump $al_loop +$al_ret: + # return (result in EAX) + c3/return |