#!/usr/bin/env python3

"""
Run gdb to disassemble a function, feed the bytes to 'llvm-mc -disassemble' command,
and display the disassembly result.

"""

from __future__ import print_function

import os
import sys
from optparse import OptionParser


def is_exe(fpath):
    """Check whether fpath is an executable."""
    return os.path.isfile(fpath) and os.access(fpath, os.X_OK)


def which(program):
    """Find the full path to a program, or return None."""
    fpath, fname = os.path.split(program)
    if fpath:
        if is_exe(program):
            return program
    else:
        for path in os.environ["PATH"].split(os.pathsep):
            exe_file = os.path.join(path, program)
            if is_exe(exe_file):
                return exe_file
    return None


def do_llvm_mc_disassembly(
        gdb_commands,
        gdb_options,
        exe,
        func,
        mc,
        mc_options):
    from io import StringIO
    import pexpect

    gdb_prompt = "\r\n\(gdb\) "
    gdb = pexpect.spawn(('gdb %s' % gdb_options) if gdb_options else 'gdb')
    # Turn on logging for what gdb sends back.
    gdb.logfile_read = sys.stdout
    gdb.expect(gdb_prompt)

    # See if there any extra command(s) to execute before we issue the file
    # command.
    for cmd in gdb_commands:
        gdb.sendline(cmd)
        gdb.expect(gdb_prompt)

    # Now issue the file command.
    gdb.sendline('file %s' % exe)
    gdb.expect(gdb_prompt)

    # Send the disassemble command.
    gdb.sendline('disassemble %s' % func)
    gdb.expect(gdb_prompt)

    # Get the output from gdb.
    gdb_output = gdb.before

    # Use StringIO to record the memory dump as well as the gdb assembler code.
    mc_input = StringIO()

    # These keep track of the states of our simple gdb_output parser.
    prev_line = None
    prev_addr = None
    curr_addr = None
    addr_diff = 0
    looking = False
    for line in gdb_output.split(os.linesep):
        if line.startswith('Dump of assembler code'):
            looking = True
            continue

        if line.startswith('End of assembler dump.'):
            looking = False
            prev_addr = curr_addr
            if mc_options and mc_options.find('arm') != -1:
                addr_diff = 4
            if mc_options and mc_options.find('thumb') != -1:
                # It is obviously wrong to assume the last instruction of the
                # function has two bytes.
                # FIXME
                addr_diff = 2

        if looking and line.startswith('0x'):
            # It's an assembler code dump.
            prev_addr = curr_addr
            curr_addr = line.split(None, 1)[0]
            if prev_addr and curr_addr:
                addr_diff = int(curr_addr, 16) - int(prev_addr, 16)

        if prev_addr and addr_diff > 0:
            # Feed the examining memory command to gdb.
            gdb.sendline('x /%db %s' % (addr_diff, prev_addr))
            gdb.expect(gdb_prompt)
            x_output = gdb.before
            # Get the last output line from the gdb examine memory command,
            # split the string into a 3-tuple with separator '>:' to handle
            # objc method names.
            memory_dump = x_output.split(
                os.linesep)[-1].partition('>:')[2].strip()
            # print "\nbytes:", memory_dump
            disasm_str = prev_line.partition('>:')[2]
            print('%s # %s' % (memory_dump, disasm_str), file=mc_input)

        # We're done with the processing.  Assign the current line to be
        # prev_line.
        prev_line = line

    # Close the gdb session now that we are done with it.
    gdb.sendline('quit')
    gdb.expect(pexpect.EOF)
    gdb.close()

    # Write the memory dump into a file.
    with open('disasm-input.txt', 'w') as f:
        f.write(mc_input.getvalue())

    mc_cmd = '%s -disassemble %s disasm-input.txt' % (mc, mc_options)
    print("\nExecuting command:", mc_cmd)
    os.system(mc_cmd)

    # And invoke llvm-mc with the just recorded file.
    #mc = pexpect.spawn('%s -disassemble %s disasm-input.txt' % (mc, mc_options))
    #mc.logfile_read = sys.stdout
    # print "mc:", mc
    # mc.close()


def main():
    # This is to set up the Python path to include the pexpect-2.4 dir.
    # Remember to update this when/if things change.
    scriptPath = sys.path[0]
    sys.path.append(
        os.path.join(
            scriptPath,
            os.pardir,
            os.pardir,
            'test',
            'pexpect-2.4'))

    parser = OptionParser(usage="""\
Run gdb to disassemble a function, feed the bytes to 'llvm-mc -disassemble' command,
and display the disassembly result.

Usage: %prog [options]
""")
    parser.add_option(
        '-C',
        '--gdb-command',
        type='string',
        action='append',
        metavar='COMMAND',
        default=[],
        dest='gdb_commands',
        help='Command(s) gdb executes after starting up (can be empty)')
    parser.add_option(
        '-O',
        '--gdb-options',
        type='string',
        action='store',
        dest='gdb_options',
        help="""The options passed to 'gdb' command if specified.""")
    parser.add_option('-e', '--executable',
                      type='string', action='store',
                      dest='executable',
                      help="""The executable to do disassembly on.""")
    parser.add_option(
        '-f',
        '--function',
        type='string',
        action='store',
        dest='function',
        help="""The function name (could be an address to gdb) for disassembly.""")
    parser.add_option('-m', '--llvm-mc',
                      type='string', action='store',
                      dest='llvm_mc',
                      help="""The llvm-mc executable full path, if specified.
                      Otherwise, it must be present in your PATH environment.""")

    parser.add_option(
        '-o',
        '--options',
        type='string',
        action='store',
        dest='llvm_mc_options',
        help="""The options passed to 'llvm-mc -disassemble' command if specified.""")

    opts, args = parser.parse_args()

    gdb_commands = opts.gdb_commands
    gdb_options = opts.gdb_options

    if not opts.executable:
        parser.print_help()
        sys.exit(1)
    executable = opts.executable

    if not opts.function:
        parser.print_help()
        sys.exit(1)
    function = opts.function

    llvm_mc = opts.llvm_mc if opts.llvm_mc else which('llvm-mc')
    if not llvm_mc:
        parser.print_help()
        sys.exit(1)

    # This is optional.  For example:
    # --options='-triple=arm-apple-darwin -debug-only=arm-disassembler'
    llvm_mc_options = opts.llvm_mc_options

    # We have parsed the options.
    print("gdb commands:", gdb_commands)
    print("gdb options:", gdb_options)
    print("executable:", executable)
    print("function:", function)
    print("llvm-mc:", llvm_mc)
    print("llvm-mc options:", llvm_mc_options)

    do_llvm_mc_disassembly(
        gdb_commands,
        gdb_options,
        executable,
        function,
        llvm_mc,
        llvm_mc_options)

if __name__ == '__main__':
    main()