1 # Example showing mmap syscall. 2 # Create a new segment using mmap, save the address, write to it. 3 # 4 # To run (from the subx directory): 5 # $ ./subx translate examples/ex12.subx -o examples/ex12 6 # $ ./subx run examples/ex12 7 # You shouldn't get a segmentation fault. 8 9 == code 10 # instruction effective address register displacement immediate 11 # . op subop mod rm32 base index scale r32 12 # . 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 13 14 # syscall(mmap, 0x1000) 15 bb/copy-to-EBX Mmap-new-segment/imm32 16 b8/copy-to-EAX 0x5a/imm32/mmap 17 cd/syscall 0x80/imm8 18 19 # write to *EAX to check that we have access to the newly-allocated segment 20 c7 0/subop/copy 0/mod/direct 0/rm32/EAX . . . . . 0x34/imm32 # copy to *EAX 21 22 # syscall(exit, EAX) 23 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX 24 b8/copy-to-EAX 1/imm32/exit 25 cd/syscall 0x80/imm8 26 27 == data 28 29 # various constants used here were found in the Linux sources (search for file mman-common.h) 30 Mmap-new-segment: # type mmap_arg_struct 31 # addr 32 0/imm32 33 # len 34 0x100/imm32 35 # protection flags 36 3/imm32 # PROT_READ | PROT_WRITE 37 # sharing flags 38 0x22/imm32 # MAP_PRIVATE | MAP_ANONYMOUS 39 # fd 40 -1/imm32 # since MAP_ANONYMOUS is specified 41 # offset 42 0/imm32 # since MAP_ANONYMOUS is specified 43 44 # . . vim:nowrap:textwidth=0