105 lines
3.7 KiB
Plaintext
105 lines
3.7 KiB
Plaintext
## example showing file syscalls
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# Create a file, open it for writing, write a character to it, close it, open
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# it for reading, read a character from it, close it, delete it, and return
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# the character read.
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#
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# To run (from the subx directory):
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# $ subx translate examples/ex7.subx -o examples/ex7
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# $ subx run examples/ex7
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# Expected result:
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# $ echo $?
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# 97
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== code
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# instruction effective address operand displacement immediate
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# op subop mod rm32 base index scale r32
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# 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
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# syscall(creat, Filename)
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bb/copy-to-EBX Filename/imm32
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b9/copy-to-ECX 0x180/imm32/fixed-perms
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b8/copy-to-EAX 8/imm32/creat
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cd/syscall 0x80/imm8
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# stream = syscall(open, Filename, O_WRONLY, 0) # we can't use 'fd' because it looks like a hex byte
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bb/copy-to-EBX Filename/imm32
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b9/copy-to-ECX 1/imm32/wronly
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ba/copy-to-EDX 0x180/imm32/fixed-perms
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b8/copy-to-EAX 5/imm32/open
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cd/syscall 0x80/imm8
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# save stream
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bb/copy-to-EBX Stream/imm32
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89/copy 0/mod/indirect 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to *EBX
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# syscall(write, Stream, "a", 1)
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# load stream
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bb/copy-to-EBX Stream/imm32
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8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
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#
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b9/copy-to-ECX A/imm32
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ba/copy-to-EDX 1/imm32/size
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b8/copy-to-EAX 4/imm32/write
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cd/syscall 0x80/imm8
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# syscall(close, Stream)
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# load stream
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bb/copy-to-EBX Stream/imm32
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8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
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#
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b8/copy-to-EAX 6/imm32/close
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cd/syscall 0x80/imm8
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# stream = syscall(open, Filename, O_RDONLY, 0)
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bb/copy-to-EBX Filename/imm32
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b9/copy-to-ECX 0/imm32/rdonly
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ba/copy-to-EDX 0x180/imm32/fixed-perms
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b8/copy-to-EAX 5/imm32/open
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cd/syscall 0x80/imm8
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# save Stream
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bb/copy-to-EBX Stream/imm32
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89/copy 0/mod/indirect 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to *EBX
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# syscall(read, Stream, B, 1)
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# load stream
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bb/copy-to-EBX Stream/imm32
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8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
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#
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b9/copy-to-ECX B/imm32
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ba/copy-to-EDX 1/imm32/size
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b8/copy-to-EAX 3/imm32/read
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cd/syscall 0x80/imm8
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# syscall(close, Stream)
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# load stream
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bb/copy-to-EBX Stream/imm32
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8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
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#
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b8/copy-to-EAX 6/imm32/close
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cd/syscall 0x80/imm8
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# syscall(unlink, filename)
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bb/copy-to-EBX Filename/imm32
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b8/copy-to-EAX 0xa/imm32/unlink
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cd/syscall 0x80/imm8
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# syscall(exit, b)
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# load b
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bb/copy-to-EBX B/imm32
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8b/copy 0/mod/indirect 3/rm32/EBX . . . 3/r32/EBX . . # copy *EBX to EBX
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#
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b8/copy-to-EAX 1/imm32/exit
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cd/syscall 0x80/imm8
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== data
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Stream:
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00 00 00 00
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A:
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61 00 00 00
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B:
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00 00 00 00
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Filename:
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2e 66 6f 6f 00 00 00 00
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# vim:nowrap:textwidth=0
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