44 lines
1.6 KiB
Plaintext
44 lines
1.6 KiB
Plaintext
# Example showing mmap syscall.
|
|
# Create a new segment using mmap, save the address, write to it.
|
|
#
|
|
# To run:
|
|
# $ ./translate_subx 000init.subx apps/ex12.subx
|
|
# $ ./a.elf
|
|
# You shouldn't get a segmentation fault.
|
|
|
|
== code
|
|
# 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:
|
|
# mmap(Mmap-new-segment->len)
|
|
bb/copy-to-ebx Mmap-new-segment/imm32
|
|
e8/call syscall_mmap/disp32
|
|
|
|
# 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
|
|
|
|
# exit(eax)
|
|
89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx
|
|
e8/call syscall_exit/disp32
|
|
|
|
== data
|
|
|
|
# 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
|