glibc/scripts/gen-as-const.py

#!/usr/bin/python3
# Produce headers of assembly constants from C expressions.
# Copyright (C) 2018 Free Software Foundation, Inc.
# This file is part of the GNU C Library.
#
# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# <http://www.gnu.org/licenses/>.

# The input to this script looks like:
#       #cpp-directive ...
#       NAME1
#       NAME2 expression ...
# A line giving just a name implies an expression consisting of just that name.

import argparse
import os.path
import re
import subprocess
import tempfile


def compute_c_consts(sym_data, cc):
    """Compute the values of some C constants.

    The first argument is a list whose elements are either strings
    (preprocessor directives, or the special string 'START' to
    indicate this function should insert its initial boilerplate text
    in the output there) or pairs of strings (a name and a C
    expression for the corresponding value).  Preprocessor directives
    in the middle of the list may be used to select which constants
    end up being evaluated using which expressions.

    """
    out_lines = []
    for arg in sym_data:
        if isinstance(arg, str):
            if arg == 'START':
                out_lines.append('void\ndummy (void)\n{')
            else:
                out_lines.append(arg)
            continue
        name = arg[0]
        value = arg[1]
        out_lines.append('asm ("@@@name@@@%s@@@value@@@%%0@@@end@@@" '
                         ': : \"i\" ((long int) (%s)));'
                         % (name, value))
    out_lines.append('}')
    out_lines.append('')
    out_text = '\n'.join(out_lines)
    with tempfile.TemporaryDirectory() as temp_dir:
        c_file_name = os.path.join(temp_dir, 'test.c')
        s_file_name = os.path.join(temp_dir, 'test.s')
        with open(c_file_name, 'w') as c_file:
            c_file.write(out_text)
        # Compilation has to be from stdin to avoid the temporary file
        # name being written into the generated dependencies.
        cmd = ('%s -S -o %s -x c - < %s' % (cc, s_file_name, c_file_name))
        subprocess.check_call(cmd, shell=True)
        consts = {}
        with open(s_file_name, 'r') as s_file:
            for line in s_file:
                match = re.search('@@@name@@@([^@]*)'
                                  '@@@value@@@[^0-9Xxa-fA-F-]*'
                                  '([0-9Xxa-fA-F-]+).*@@@end@@@', line)
                if match:
                    if (match.group(1) in consts
                        and match.group(2) != consts[match.group(1)]):
                        raise ValueError('duplicate constant %s'
                                         % match.group(1))
                    consts[match.group(1)] = match.group(2)
        return consts


def gen_test(sym_data):
    """Generate a test for the values of some C constants.

    The first argument is as for compute_c_consts.

    """
    out_lines = []
    for arg in sym_data:
        if isinstance(arg, str):
            if arg == 'START':
                out_lines.append('#include <stdint.h>\n'
                                 '#include <stdio.h>\n'
                                 '#include <bits/wordsize.h>\n'
                                 '#if __WORDSIZE == 64\n'
                                 'typedef uint64_t c_t;\n'
                                 '# define U(n) UINT64_C (n)\n'
                                 '#else\n'
                                 'typedef uint32_t c_t;\n'
                                 '# define U(n) UINT32_C (n)\n'
                                 '#endif\n'
                                 'static int\n'
                                 'do_test (void)\n'
                                 '{\n'
                                 # Compilation test only, using static
                                 # assertions.
                                 '  return 0;\n'
                                 '}\n'
                                 '#include <support/test-driver.c>')
            else:
                out_lines.append(arg)
            continue
        name = arg[0]
        value = arg[1]
        out_lines.append('_Static_assert (U (asconst_%s) == (c_t) (%s), '
                         '"value of %s");'
                         % (name, value, name))
    return '\n'.join(out_lines)


def main():
    """The main entry point."""
    parser = argparse.ArgumentParser(
        description='Produce headers of assembly constants.')
    parser.add_argument('--cc', metavar='CC',
                        help='C compiler (including options) to use')
    parser.add_argument('--test', action='store_true',
                        help='Generate test case instead of header')
    parser.add_argument('sym_file',
                        help='.sym file to process')
    args = parser.parse_args()
    sym_data = []
    with open(args.sym_file, 'r') as sym_file:
        started = False
        for line in sym_file:
            line = line.strip()
            if line == '':
                continue
            # Pass preprocessor directives through.
            if line.startswith('#'):
                sym_data.append(line)
                continue
            words = line.split(maxsplit=1)
            if not started:
                sym_data.append('START')
                started = True
            # Separator.
            if words[0] == '--':
                continue
            name = words[0]
            value = words[1] if len(words) > 1 else words[0]
            sym_data.append((name, value))
        if not started:
            sym_data.append('START')
    if args.test:
        print(gen_test(sym_data))
    else:
        consts = compute_c_consts(sym_data, args.cc)
        print(''.join('#define %s %s\n' % c for c in sorted(consts.items())), end='')

if __name__ == '__main__':
    main()