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 operand 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 # mmap(0x1000) 15 bb/copy . . . . . . . mmap_new_segment/imm32 # copy to EBX 16 b8/copy . . . . . . . 0x5a/imm32/mmap # copy to EAX 17 cd/syscall 0x80/imm8 18 19 # store to *EAX 20 c7/copy 0/mod/direct 0/rm32/EAX . . . . . 0x34/imm32 # copy to *EAX 21 22 # exit(EAX) 23 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX 24 b8/copy . . . . . . . 1/imm32/exit # copy to EAX 25 cd/syscall 0x80/imm8 26 27 == data 28 # various constants used here were found in the Linux sources (search for file mman-common.h) 29 mmap_new_segment: # type mmap_arg_struct 30 # addr 31 00 00 00 00 # null 32 # len 33 00 01 00 00 # 0x1000 34 # protection flags 35 03 00 00 00 # PROT_READ | PROT_WRITE 36 # sharing flags 37 22 00 00 00 # MAP_PRIVATE | MAP_ANONYMOUS 38 # fd 39 ff ff ff ff # -1 since MAP_ANONYMOUS is specified 40 # offset 41 00 00 00 00 # 0 since MAP_ANONYMOUS is specified 42 43 # vim:ft=subx:nowrap:tw&