build_tools/marshal.py

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"""Marshal another python script.

This script compiles another script, marshals the resulting code object, and
writes it to stdout. Marshalling an object in this sense is essentially what
would happen to write it out in a pyc file.

This code object can then be read back in by another python script later and
executed, without having to have access to the original file. This is how
python code is embedded into the gem5 binary.

The output of the marshal module is *not* generally compatible accross python
interpretters, and so the exact same interpretter should be used both to run
this script, and to read in and execute the marshalled code later.
"""

import marshal
import sys
import zlib

from blob import bytesToCppArray
from code_formatter import code_formatter

# Embed python files.  All .py files that have been indicated by a
# PySource() call in a SConscript need to be embedded into the M5
# library.  To do that, we compile the file to byte code, marshal the
# byte code, compress it, and then generate a c++ file that
# inserts the result into an array.

if len(sys.argv) < 4:
    print(f"Usage: {sys.argv[0]} CPP PY MODPATH ABSPATH", file=sys.stderr)
    sys.exit(1)

_, cpp, python, modpath, abspath = sys.argv

with open(python, "r") as f:
    src = f.read()

compiled = compile(src, python, "exec")
marshalled = marshal.dumps(compiled)

compressed = zlib.compress(marshalled)

code = code_formatter()
code(
    """\
#include "python/embedded.hh"

namespace gem5
{
namespace
{

"""
)

bytesToCppArray(code, "embedded_module_data", compressed)

# The name of the EmbeddedPython object doesn't matter since it's in an
# anonymous namespace, and it's constructor takes care of installing it into a
# global list.
code(
    """
EmbeddedPython embedded_module_info(
    "${abspath}",
    "${modpath}",
    embedded_module_data,
    ${{len(compressed)}},
    ${{len(marshalled)}});

} // anonymous namespace
} // namespace gem5
"""
)

code.write(cpp)