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disassembler.py
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disassembler.py
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import struct
import StringIO
Inst = struct.Struct("BBHI")
CLASSES = {
0: "ld",
1: "ldx",
2: "st",
3: "stx",
4: "alu",
5: "jmp",
7: "alu64",
}
ALU_OPCODES = {
0: 'add',
1: 'sub',
2: 'mul',
3: 'div',
4: 'or',
5: 'and',
6: 'lsh',
7: 'rsh',
8: 'neg',
9: 'mod',
10: 'xor',
11: 'mov',
12: 'arsh',
13: '(endian)',
}
JMP_OPCODES = {
0: 'ja',
1: 'jeq',
2: 'jgt',
3: 'jge',
4: 'jset',
5: 'jne',
6: 'jsgt',
7: 'jsge',
8: 'call',
9: 'exit',
10: 'jlt',
11: 'jle',
12: 'jslt',
13: 'jsle',
}
MODES = {
0: 'imm',
1: 'abs',
2: 'ind',
3: 'mem',
6: 'xadd',
}
SIZES = {
0: 'w',
1: 'h',
2: 'b',
3: 'dw',
}
BPF_CLASS_LD = 0
BPF_CLASS_LDX = 1
BPF_CLASS_ST = 2
BPF_CLASS_STX = 3
BPF_CLASS_ALU = 4
BPF_CLASS_JMP = 5
BPF_CLASS_ALU64 = 7
BPF_ALU_NEG = 8
BPF_ALU_END = 13
def R(reg):
return "r" + str(reg)
def I(imm):
return "%#x" % imm
def M(base, off):
if off != 0:
return "[%s%s]" % (base, O(off))
else:
return "[%s]" % base
def O(off):
if off <= 32767:
return "+" + str(off)
else:
return "-" + str(65536-off)
def disassemble_one(data, offset):
code, regs, off, imm = Inst.unpack_from(data, offset)
dst_reg = regs & 0xf
src_reg = (regs >> 4) & 0xf
cls = code & 7
class_name = CLASSES.get(cls)
if cls == BPF_CLASS_ALU or cls == BPF_CLASS_ALU64:
source = (code >> 3) & 1
opcode = (code >> 4) & 0xf
opcode_name = ALU_OPCODES.get(opcode)
if cls == BPF_CLASS_ALU:
opcode_name += "32"
if opcode == BPF_ALU_END:
opcode_name = source == 1 and "be" or "le"
return "%s%d %s" % (opcode_name, imm, R(dst_reg))
elif opcode == BPF_ALU_NEG:
return "%s %s" % (opcode_name, R(dst_reg))
elif source == 0:
return "%s %s, %s" % (opcode_name, R(dst_reg), I(imm))
else:
return "%s %s, %s" % (opcode_name, R(dst_reg), R(src_reg))
elif cls == BPF_CLASS_JMP:
source = (code >> 3) & 1
opcode = (code >> 4) & 0xf
opcode_name = JMP_OPCODES.get(opcode)
if opcode_name == "exit":
return opcode_name
elif opcode_name == "call":
return "%s %s" % (opcode_name, I(imm))
elif opcode_name == "ja":
return "%s %s" % (opcode_name, O(off))
elif source == 0:
return "%s %s, %s, %s" % (opcode_name, R(dst_reg), I(imm), O(off))
else:
return "%s %s, %s, %s" % (opcode_name, R(dst_reg), R(src_reg), O(off))
elif cls == BPF_CLASS_LD or cls == BPF_CLASS_LDX or cls == BPF_CLASS_ST or cls == BPF_CLASS_STX:
size = (code >> 3) & 3
mode = (code >> 5) & 7
mode_name = MODES.get(mode, str(mode))
# TODO use different syntax for non-MEM instructions
size_name = SIZES.get(size, str(size))
if code == 0x18: # lddw
_, _, _, imm2 = Inst.unpack_from(data, offset+8)
imm = (imm2 << 32) | imm
return "%s %s, %s" % (class_name + size_name, R(dst_reg), I(imm))
elif code == 0x00:
# Second instruction of lddw
return None
elif cls == BPF_CLASS_LDX:
return "%s %s, %s" % (class_name + size_name, R(dst_reg), M(R(src_reg), off))
elif cls == BPF_CLASS_ST:
return "%s %s, %s" % (class_name + size_name, M(R(dst_reg), off), I(imm))
elif cls == BPF_CLASS_STX:
return "%s %s, %s" % (class_name + size_name, M(R(dst_reg), off), R(src_reg))
else:
return "unknown mem instruction %#x" % code
else:
return "unknown instruction %#x" % code
def disassemble(data):
output = StringIO.StringIO()
offset = 0
while offset < len(data):
s = disassemble_one(data, offset)
if s:
output.write(s + "\n")
offset += 8
return output.getvalue()