diff options
Diffstat (limited to 'subx/examples/ex7.subx')
| -rw-r--r-- | subx/examples/ex7.subx | 139 |
1 files changed, 87 insertions, 52 deletions
diff --git a/subx/examples/ex7.subx b/subx/examples/ex7.subx index 86e018c8..6f8d3979 100644 --- a/subx/examples/ex7.subx +++ b/subx/examples/ex7.subx @@ -1,64 +1,99 @@ -## compute the factorial of 5, and return the result in the exit code +## 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. # # To run: -# $ subx translate ex7.subx ex7 -# $ subx run ex7 +# $ subx translate ex8.subx ex8 +# $ subx run ex8 # Expected result: # $ echo $? -# 120 +# 97 -== 0x08048054 # code segment, after leaving room for ELF header +== 0x08048074 # 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 -# main: - # prepare to make a call - 55/push . . . . . . . . # push EBP - 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP - # factorial(5) - 68/push . . . . . . . 5/imm32 # push 5 - e8/call . . . . . . factorial/disp32 - # discard arg - 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 + ## 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 - # exit(EAX) - 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX - b8/copy . . . . . . . 1/imm32 # copy 1 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 -# factorial(n) -factorial: - # initialize n - 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 2/r32/EDX 4/disp8 . # copy *(ESP+4) to EDX - # initialize EAX to 1 (base case) - b8/copy . . . . . . . 1/imm32 # copy 1 to EAX - # if (n <= 1) jump exit - 81 7/subop/compare 3/mod/direct 2/rm32/EDX . . . . . 1/imm32 # compare EDX with 1 - 7e/jump-if-<= . . . . . . $factorial:exit/disp8 # jump if <= to $factorial:exit - # EBX: n-1 - 89/copy 3/mod/direct 3/rm32/EBX . . . 2/r32/EDX . . # copy EDX to EBX - 81 5/subop/subtract 3/mod/direct 3/rm32/EBX . . . . . 1/imm32 # subtract 1 from EBX - # prepare call - 55/push . . . . . . . . # push EBP - 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP - # EAX: factorial(n-1) - 53/push . . . . . . . . # push EBX - e8/call . . . . . . factorial/disp32 - # discard arg - 5e/pop . . . . . . . . # pop into ESI - # clean up after call - 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP - 5d/pop . . . . . . . . # pop to EBP - # refresh n - 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 2/r32/EDX 4/disp8 . # copy *(ESP+4) to EDX - # return n * factorial(n-1) - 0f af/multiply 3/mod/direct 2/rm32/EDX . . . 0/r32/EAX . . # multiply EDX (n) into EAX (factorial(n-1)) - # TODO: check for overflow -$factorial:exit: - c3/return + ## 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 -# vim:ft=subx:nowrap:so=0 + ## 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 + # + 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& |