Abstract calls to native functions

[elicn]

Users may now stage and call native functions without having to do manual frame setup.
This code abstracts away the need to create a new frame, write the arguments, set the return address and pc.

Example:

from qiling.os.const import *

# the address of the function we are about to call
func_entry = 0xdeadc0de

# save current pc value and use it to resume execution
retaddr = ql.reg.arch_pc

# call a function that recieves 3 arguments, whose entry is at 'func_entry'
ql.os.fcall.call_native(func_entry, (
    (POINTER, x),
    (POINTER, y),
    (POINTER, z)
), retaddr)

Notes:

• Currently supports plain arguments types (i.e. integer values tagged with POINTER, INT, etc.); support for complex types like STRING and GUID may be added in the future
• Implemented for Intel and ARM architectures, not yet for MIPS and RISC
• The retaddr arg may be used to either resume execution from an arbitrary address, or force the execution flow into a hook to regain control (e.g. in case a cleanup is needed)

[xwings]

ah, this is nice