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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 examples/ex7.subx -o examples/ex7
# $ ./subx run examples/ex7
# Expected result:
# $ echo $?
# 97
== code 0x09000000
# 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:
# 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 0x0a000000
Stream:
0/imm32
A:
61/imm32/A
B:
0/imm32
Filename:
2e 66 6f 6f 00 00 00 00
# . f o o null
# . . vim:nowrap:textwidth=0
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