How to dereference a memory location from python ctypes?
21,283
ctypes.cast
.
>>> import ctypes
>>> c_long_p = ctypes.POINTER(ctypes.c_long)
>>> some_long = ctypes.c_long(42)
>>> ctypes.addressof(some_long)
4300833936
>>> ctypes.cast(4300833936, c_long_p)
<__main__.LP_c_long object at 0x1005983b0>
>>> ctypes.cast(4300833936, c_long_p).contents
c_long(42)
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Updated on October 13, 2020Comments
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Admin over 3 years
I want to replicate the following c code in python ctypes:
main() { long *ptr = (long *)0x7fff96000000; printf("%lx",*ptr); }
I can figure out how to call this memory location as a function pointer but not just do a normal dereference:
from ctypes import * """ >>> fptr = CFUNCTYPE(None, None) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python2.6/ctypes/__init__.py", line 104, in CFUNCTYPE class CFunctionType(_CFuncPtr): TypeError: Error when calling the metaclass bases item 1 in _argtypes_ has no from_param method """ fptr = CFUNCTYPE(None, c_void_p) #add c_void_p since you have to have an arg fptr2 = fptr(0x7fff96000000) fptr2(c_void_p(0)) #python: segfault at 7fff96000000 ip 00007fff96000000
Since there it is a segfault with the instruction pointer pointing to this memory location it is successfully calling it. However I can't get it to just read the memory location:
ptr = POINTER(c_long) ptr2 = ptr(c_long(0x7fff96000000)) #>>> ptr2[0] #140735709970432 #>>> hex(ptr2[0]) #'0x7fff96000000' #>>> ptr2.contents #c_long(140735709970432)