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Diffstat (limited to 'examples/ex12.subx')
| -rw-r--r-- | examples/ex12.subx | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/examples/ex12.subx b/examples/ex12.subx new file mode 100644 index 00000000..358da1d3 --- /dev/null +++ b/examples/ex12.subx @@ -0,0 +1,45 @@ +# 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 |