45 lines
1.7 KiB
Plaintext
45 lines
1.7 KiB
Plaintext
# Example showing mmap syscall.
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# Create a new segment using mmap, save the address, write to it.
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#
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# To run (from the subx directory):
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# $ ./subx translate examples/ex12.subx -o examples/ex12
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# $ ./subx run examples/ex12
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# You shouldn't get a segmentation fault.
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== code
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# instruction effective address register 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(mmap, 0x1000)
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bb/copy-to-EBX Mmap-new-segment/imm32
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b8/copy-to-EAX 0x5a/imm32/mmap
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cd/syscall 0x80/imm8
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# write to *EAX to check that we have access to the newly-allocated segment
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c7 0/subop/copy 0/mod/direct 0/rm32/EAX . . . . . 0x34/imm32 # copy to *EAX
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# syscall(exit, EAX)
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89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX
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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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# various constants used here were found in the Linux sources (search for file mman-common.h)
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Mmap-new-segment: # type mmap_arg_struct
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# addr
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0/imm32
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# len
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0x100/imm32
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# protection flags
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3/imm32 # PROT_READ | PROT_WRITE
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# sharing flags
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0x22/imm32 # MAP_PRIVATE | MAP_ANONYMOUS
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# fd
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-1/imm32 # since MAP_ANONYMOUS is specified
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# offset
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0/imm32 # since MAP_ANONYMOUS is specified
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# . . vim:nowrap:textwidth=0
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