64 lines
2.9 KiB
Plaintext
64 lines
2.9 KiB
Plaintext
# Create a new segment (for data) using mmap().
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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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# main: (manual test if this is the last file loaded)
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# EAX = new-segment(0x1000)
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# . . push args
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68/push 0x1000/imm32
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# . . call
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e8/call new-segment/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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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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new-segment: # len : int -> address
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# . prolog
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55/push-EBP
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89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
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53/push-EBX
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# copy len to _mmap-new-segment->len
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# TODO: compute _mmap-new-segment+4 before runtime
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8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 0/r32/EAX 8/disp8 . # copy *(EBP+8) to EAX
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bb/copy-to-EBX _mmap-new-segment/imm32
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89/copy 1/mod/*+disp8 3/rm32/EBX . . . 0/r32/EAX 4/disp8 . # copy EAX to *(EBX+4)
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# mmap(_mmap-new-segment)
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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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$new-segment:end:
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# . epilog
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5b/pop-to-EBX
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89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
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5d/pop-to-EBP
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c3/return
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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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00 00 00 00 # null
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# len
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00 00 00 00 # 0x1000
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# protection flags
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03 00 00 00 # PROT_READ | PROT_WRITE
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# sharing flags
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22 00 00 00 # MAP_PRIVATE | MAP_ANONYMOUS
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# fd
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ff ff ff ff # -1 since MAP_ANONYMOUS is specified
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# offset
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00 00 00 00 # 0 since MAP_ANONYMOUS is specified
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# . . vim:nowrap:textwidth=0
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