def assemble(code):
"""
Assemble the given iterable of mnemonics, operands, and lables.
A convienience over constructing individual Instruction and Operand
objects, the output of this function can be directly piped to
:class:`~jawa.attributes.code.CodeAttribute.assemble()` to produce
executable bytecode.
As a simple example, lets produce an infinite loop:
>>> from jawa.assemble import assemble, Label
>>> print(list(assemble((
... Label('start'),
... ('goto', Label('start'))
... ))))
[Instruction(mnemonic='goto', opcode=167, operands=[
Operand(op_type=40, value=0)], pos=0)]
For a more complex example, see examples/hello_world.py.
"""
final = []
# We need to make three passes, because we cannot know the offset for
# jump labels until after we've figured out the PC for each instructions,
# which is complicated by the variable-width instructions set and
# alignment padding.
for line in code:
if isinstance(line, Label):
final.append(line)
continue
mnemonic, operands = line[0], line[1:]
operand_fmts = definition_from_mnemonic(mnemonic)[1]
# We need to coerce each opcodes operands into their
# final `Operand` form.
final_operands = []
for i, operand in enumerate(operands):
if isinstance(operand, Operand):
# Already in Operand form.
final_operands.append(operand)
elif isinstance(operand, Constant):
# Convert constants into CONSTANT_INDEX'es
final_operands.append(Operand(OperandTypes.CONSTANT_INDEX, operand.index))
elif isinstance(operand, dict):
# lookupswitch's operand is a dict as
# a special usability case.
final_operands.append(operand)
elif isinstance(operand, Label):
final_operands.append(operand)
else:
# For anything else, lookup that opcode's operand
# type from its definition.
final_operands.append(Operand(operand_fmts[i][1], operand))
# Build the final, immutable `Instruction`.
final.append(Instruction.from_mnemonic(mnemonic, operands=final_operands))
label_pcs = {}
# The second pass, find the absolute PC for each label.
current_pc = 0
for ins in final:
if isinstance(ins, Label):
label_pcs[ins.name] = current_pc
continue
# size_on_disk must know the current pc because of alignment on
# tableswitch and lookupswitch.
current_pc += ins.size_on_disk(current_pc)
# The third pass, now that we know where each label is we can figure
# out the offset for each jump.
current_pc = 0
offset = lambda l: Operand(40, label_pcs[l.name] - current_pc)
for ins in final:
if isinstance(ins, Label):
continue
for i, operand in enumerate(ins.operands):
if isinstance(operand, dict):
# lookupswitch is a special case
for k, v in operand.items():
if isinstance(v, Label):
operand[k] = offset(v)
elif isinstance(operand, Label):
ins.operands[i] = offset(operand)
current_pc += ins.size_on_disk(current_pc)
yield ins
def assemble(code):
"""
A convienience method for 'assembling' bytecode over the regular
:meth:`~jawa.attributes.code.CodeAttribute.assemble()` method with
support for labels and direct constants.
"""
final = []
# We need to make three passes, because we cannot know the offset for
# jump labels until after we've figured out the PC for each instructions,
# which is complicated by the variable-width instructions set and
# alignment padding.
for line in code:
if isinstance(line, Label):
final.append(line)
continue
mnemonic, operands = line[0], line[1:]
operand_fmts = definition_from_mnemonic(mnemonic)[1]
# We need to coerce each opcodes operands into their
# final `Operand` form.
final_operands = []
for i, operand in enumerate(operands):
if isinstance(operand, Operand):
# Already in Operand form.
final_operands.append(operand)
elif isinstance(operand, Constant):
# Convert constants into CONSTANT_INDEX'es
final_operands.append(Operand(
OperandTypes.CONSTANT_INDEX,
operand.index
))
elif isinstance(operand, dict):
# lookupswitch's operand is a dict as
# a special usability case.
final_operands.append(operand)
elif isinstance(operand, Label):
final_operands.append(operand)
else:
# For anything else, lookup that opcode's operand
# type from its definition.
final_operands.append(Operand(
operand_fmts[i][1],
operand
))
# Build the final, immutable `Instruction`.
final.append(Instruction.from_mnemonic(
mnemonic,
operands=final_operands
))
label_pcs = {}
# The second pass, find the absolute PC for each label.
current_pc = 0
for ins in final:
if isinstance(ins, Label):
label_pcs[ins.name] = current_pc
continue
# size_on_disk must know the current pc because of alignment on
# tableswitch and lookupswitch.
current_pc += ins.size_on_disk(current_pc)
# The third pass, now that we know where each label is we can figure
# out the offset for each jump.
current_pc = 0
offset = lambda l: Operand(40, label_pcs[l.name] - current_pc)
for ins in final:
if isinstance(ins, Label):
continue
for i, operand in enumerate(ins.operands):
if isinstance(operand, dict):
# lookupswitch is a special case
for k, v in operand.items():
if isinstance(v, Label):
operand[k] = offset(v)
elif isinstance(operand, Label):
ins.operands[i] = offset(operand)
current_pc += ins.size_on_disk(current_pc)
yield ins
