## 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 (from the subx directory):
# $ subx translate examples/ex7.subx -o examples/ex7
# $ subx run examples/ex7
# 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
# syscall(creat, filename)
bb/copy-to-EBX filename/imm32
b9/copy-to-ECX 0x180/imm32/fixed-perms
b8/copy-to-EAX 8/imm32/creat
cd/syscall 0x80/imm8
# stream = syscall(open, filename, O_WRONLY, 0) # we can't use 'fd' because it looks like a hex byte
bb/copy-to-EBX filename/imm32
b9/copy-to-ECX 1/imm32/wronly
ba/copy-to-EDX 0x180/imm32/fixed-perms
b8/copy-to-EAX 5/imm32/open
cd/syscall 0x80/imm8
# save stream
bb/copy-to-EBX stream/imm32
89/copy 0/mod/indirect 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to *EBX
# syscall(write, stream, "a", 1)
# load stream
bb/copy-to-EBX stream/imm32
8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
#
b9/copy-to-ECX a/imm32
ba/copy-to-EDX 1/imm32/size
b8/copy-to-EAX 4/imm32/write
cd/syscall 0x80/imm8
# syscall(close, stream)
# load stream
bb/copy-to-EBX stream/imm32
8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
#
b8/copy-to-EAX 6/imm32/close
cd/syscall 0x80/imm8
# stream = syscall(open, filename, O_RDONLY, 0)
bb/copy-to-EBX filename/imm32
b9/copy-to-ECX 0/imm32/rdonly
ba/copy-to-EDX 0x180/imm32/fixed-perms
b8/copy-to-EAX 5/imm32/open
cd/syscall 0x80/imm8
# save stream
bb/copy-to-EBX stream/imm32
89/copy 0/mod/indirect 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to *EBX
# syscall(read, stream, b, 1)
# load stream
bb/copy-to-EBX stream/imm32
8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
#
b9/copy-to-ECX b/imm32
ba/copy-to-EDX 1/imm32/size
b8/copy-to-EAX 3/imm32/read
cd/syscall 0x80/imm8
# syscall(close, stream)
# load stream
bb/copy-to-EBX stream/imm32
8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
#
b8/copy-to-EAX 6/imm32/close
cd/syscall 0x80/imm8
# syscall(unlink, filename)
bb/copy-to-EBX filename/imm32
b8/copy-to-EAX 0xa/imm32/unlink
cd/syscall 0x80/imm8
# syscall(exit, b)
# load b
bb/copy-to-EBX b/imm32
8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
#
b8/copy-to-EAX 1/imm32/exit
cd/syscall 0x80/imm8
== data
stream:
00 00 00 00
a:
61 00 00 00
b:
00 00 00 00
filename:
2e 66 6f 6f 00 00 00 00
# vim:nowrap:textwidth=0