Module designed to modify Python bytecode. Allows instructions to be added or removed from a Python bytecode string. The modified bytecode can be refactored to correct offsets and produce a new functional code object.
You should use the same Python interpretor version as the bytecode being analyzed.
The following example inserts a NOP instruction after each instruction in the Sample function:
import bytecode_graph
from dis import opmap
def Sample():
i = 2 + 2
if i == 4:
print "2 + 2 = %d" % i
else:
print "oops"
print bytecode_graph.disassemble(Sample.__code__)
print
bcg = bytecode_graph.BytecodeGraph(Sample.__code__)
nodes = [x for x in bcg.nodes()]
for n in nodes:
bc = bytecode_graph.Bytecode(0, chr(opmap['NOP']))
bcg.add_node(n, bc)
new_code = bcg.get_code()
print bytecode_graph.disassemble(new_code)
print
exec new_code
nodes = [x for x in bcg.nodes()]
for n in nodes:
if n.opcode == opmap['NOP']:
bcg.delete_node(n)
new_code = bcg.get_code()
print bytecode_graph.disassemble(new_code)
exec new_codeDisassembly of Sample():
0 640500 LOAD_CONST 5 (4)
3 7d0000 STORE_FAST 0 (i)
6 7c0000 LOAD_FAST 0 (i)
9 640200 LOAD_CONST 2 (4)
12 6b0200 COMPARE_OP 2 (==)
15 721e00 POP_JUMP_IF_FALSE 30
18 640300 LOAD_CONST 3 ('2 + 2 = %d')
21 7c0000 LOAD_FAST 0 (i)
24 16 BINARY_MODULO
25 47 PRINT_ITEM
26 48 PRINT_NEWLINE
27 6e0500 JUMP_FORWARD 5 (to 35)
>> 30 640400 LOAD_CONST 4 ('oops')
33 47 PRINT_ITEM
34 48 PRINT_NEWLINE
>> 35 640000 LOAD_CONST 0 (None)
38 53 RETURN_VALUE
Disassembly of Sample() with NOPs:
0 640500 LOAD_CONST 5 (4)
3 09 NOP
4 7d0000 STORE_FAST 0 (i)
7 09 NOP
8 7c0000 LOAD_FAST 0 (i)
11 09 NOP
12 640200 LOAD_CONST 2 (4)
15 09 NOP
16 6b0200 COMPARE_OP 2 (==)
19 09 NOP
20 722a00 POP_JUMP_IF_FALSE 42
23 09 NOP
24 640300 LOAD_CONST 3 ('2 + 2 = %d')
27 09 NOP
28 7c0000 LOAD_FAST 0 (i)
31 09 NOP
32 16 BINARY_MODULO
33 09 NOP
34 47 PRINT_ITEM
35 09 NOP
36 48 PRINT_NEWLINE
37 09 NOP
38 6e0900 JUMP_FORWARD 9 (to 50)
41 09 NOP
>> 42 640400 LOAD_CONST 4 ('oops')
45 09 NOP
46 47 PRINT_ITEM
47 09 NOP
48 48 PRINT_NEWLINE
49 09 NOP
>> 50 640000 LOAD_CONST 0 (None)
53 09 NOP
54 53 RETURN_VALUE
55 09 NOP
Output of running modified code object:
2 + 2 = 4
To remove the NOPs append the following to the above example:
nodes = [x for x in bcg.nodes()]
for n in nodes:
#verify opcode is NOP
if n.opcode == opmap['NOP']:
#remove instruction node from the graph
bcg.delete_node(n)
#create a new code object
new_code = bcg.get_code()
bytecode_graph.disassemble(new_code)
exec new_codeTo load code from a PYC file:
import bytecode_graph
from dis import opmap
import sys
import marshal
pyc_file = open(sys.argv[1], "rb").read()
pyc = marshal.loads(pyc_file[8:])
bytecode_graph.disassemble(pyc)
print
bcg = bytecode_graph.BytecodeGraph(pyc)
nodes = [x for x in bcg.nodes()]
for n in nodes:
bc = bytecode_graph.Bytecode(0, chr(opmap['NOP']))
bcg.add_node(n, bc)
new_code = bcg.get_code()
bytecode_graph.disassemble(new_code)
print
nodes = [x for x in bcg.nodes()]
for n in nodes:
if n.opcode == opmap['NOP']:
bcg.delete_node(n)
new_code = bcg.get_code()
bytecode_graph.disassemble(new_code)
printIt is also possible to create control flow diagrams using GraphViz. The disassembly within the graph can include the output from a simple peephole decompiler. This can be helpful when reviewing bytecode that fails to decompile.
import bytecode_graph
def Sample():
i = 2 + 2
if i == 4:
print "2 + 2 = %d" % i
else:
print "oops"
bcg = bytecode_graph.BytecodeGraph(Sample.__code__)
graph = bytecode_graph.Render(bcg, Sample.__code__).dot()
graph.write_png('example_graph.png')
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