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# Example showing mmap syscall.
# Create a new segment using mmap, save the address, write to it.
#
# To run (from the subx directory):
# $ ./subx translate examples/ex12.subx -o examples/ex12
# $ ./subx run examples/ex12
# You shouldn't get a segmentation fault.
== code 0x09000000
# instruction effective address register displacement immediate
# . op subop mod rm32 base index scale r32
# . 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
Entry:
# syscall(mmap, 0x1000)
bb/copy-to-EBX Mmap-new-segment/imm32
b8/copy-to-EAX 0x5a/imm32/mmap
cd/syscall 0x80/imm8
# write to *EAX to check that we have access to the newly-allocated segment
c7 0/subop/copy 0/mod/direct 0/rm32/EAX . . . . . 0x34/imm32 # copy to *EAX
# syscall(exit, EAX)
89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX
b8/copy-to-EAX 1/imm32/exit
cd/syscall 0x80/imm8
== data 0x0a000000
# various constants used here were found in the Linux sources (search for file mman-common.h)
Mmap-new-segment: # type mmap_arg_struct
# addr
0/imm32
# len
0x100/imm32
# protection flags
3/imm32 # PROT_READ | PROT_WRITE
# sharing flags
0x22/imm32 # MAP_PRIVATE | MAP_ANONYMOUS
# fd
-1/imm32 # since MAP_ANONYMOUS is specified
# offset
0/imm32 # since MAP_ANONYMOUS is specified
# . . vim:nowrap:textwidth=0
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