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generated by cgit-pink 1.4.1-2-gfad0 (git 2.36.2.497.gbbea4dcf42) at 2024-11-14 12:12:25 +0000


 



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## 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 ex8.subx ex8
#   $ subx run ex8
# Expected result:
#   $ echo $?
#   97

== code
# 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
  #
  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&