44 lines
1.7 KiB
Plaintext
44 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:
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# $ bootstrap/bootstrap translate ex12.subx -o ex12
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# $ bootstrap/bootstrap run 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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Entry:
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# mmap(Mmap-new-segment->len)
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bb/copy-to-ebx Mmap-new-segment/imm32
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e8/call syscall_mmap/disp32
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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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# 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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e8/call syscall_exit/disp32
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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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