[PATCH v2] Add scripts/move-symbol-to-libc.py

[Florian Weimer <fw@deneb.enyo.de>]

This helper script can be used to move symbols to libc.abilist across
all architectures, while preserving their symbol version.

---
 scripts/move-symbol-to-libc.py | 217 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 217 insertions(+)

diff --git a/scripts/move-symbol-to-libc.py b/scripts/move-symbol-to-libc.py
new file mode 100644
index 0000000000..4863c4dd8a
--- /dev/null
+++ b/scripts/move-symbol-to-libc.py
@@ -0,0 +1,217 @@
+#!/usr/bin/python3
+# Move symbols from other shared objects into libc.so.
+# Copyright (C) 2020 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
+# <https://www.gnu.org/licenses/>.
+
+"""Move symbols from other shared objects into libc.so.
+
+This script moves ABI symbols from non-libc abilists in to
+libc.abilist.  Symbol versions are preserved.  The script must be
+called from the top of the glibc source tree.
+
+"""
+
+import argparse
+import os.path
+import sys
+
+def replace_file(path, new_contents):
+    """Atomically replace PATH with lines from NEW_CONTENTS.
+
+    NEW_CONTENTS must be a sequence of strings.
+
+    """
+    temppath = path + 'T'
+    with open(temppath, 'w') as out:
+        for line in new_contents:
+            out.write(line)
+    os.rename(temppath, path)
+
+class VersionedSymbol:
+    """A combination of a symbol and its version."""
+
+    def __init__(self, symbol, version):
+        """Construct a new versioned symbol."""
+        assert symbol
+        assert version
+        self.symbol = symbol
+        self.version = version
+
+    def __str__(self):
+        return self.symbol + '@' + self.version
+
+    def __eq__(self, other):
+        return self.symbol == other.symbol and self.version == other.version
+
+    def __hash__(self):
+        return hash(self.symbol) ^ hash(self.version)
+
+def read_abilist(path):
+    """Read the abilist file at PATH.
+
+    Return a dictionary from VersionedSymbols to their flags (as
+    strings).
+
+    """
+    result = {}
+    with open(path) as inp:
+        for line in inp:
+            version, symbol, flags = line.strip().split(' ', 2)
+            result[VersionedSymbol(symbol, version)] = flags
+    return result
+
+def abilist_lines(symbols):
+    """Build the abilist file contents (as a list of lines).
+
+    SYMBOLS is a dictionary from VersionedSymbols to their flags.
+
+    """
+    result = []
+    for versym, flags in symbols.items():
+        result.append('{} {} {}\n'.format(
+            versym.version, versym.symbol, flags))
+    result.sort()
+    return result
+
+def add_to_libc_path(path, new_symbols):
+    """Add SYMBOLS to the abilist file PATH.
+
+    NEW_SYMBOLS is a dictionary from VersionedSymbols to their flags.
+
+    """
+    original_symbols = read_abilist(path)
+    updated_symbols = original_symbols.copy()
+    updated_symbols.update(new_symbols)
+    if updated_symbols != original_symbols:
+        sys.stdout.write('updating libc abilist {}\n'.format(path))
+        replace_file(path, abilist_lines(updated_symbols))
+
+# The name of the libc.so abilist file.
+libc_abilist = 'libc.abilist'
+
+def add_to_libc_fallback(directory, subdirs, symbol_lines):
+    """Add SYMBOL_LINES to the libc.abilist files in SUBDIRS in DIRECTORY.
+
+    All subdirectories must exist.  If they do, return True.  If not,
+    skip processing and return False.
+
+    """
+    abilists = [os.path.join(directory, subdir, libc_abilist)
+                for subdir in subdirs]
+    for abilist in abilists:
+        if not os.path.exists(abilist):
+            return False
+    for abilist in abilists:
+            add_to_libc_path(abilist, symbol_lines)
+    return True
+
+def add_to_libc(directory, symbol_lines):
+
+    """Add SYMBOL_LINES (a list of strings) to libc.abilist in DIRECTORY.
+
+    Try specific subdirectories as well if libc.abilist is not found
+    in DIRECTORY.
+
+    """
+    libc_path = os.path.join(directory, libc_abilist)
+    if os.path.exists(libc_path):
+        add_to_libc_path(libc_path, symbol_lines)
+        return
+
+    # Special case for powerpc32 and mips32 variants.
+    if add_to_libc_fallback(directory, ('fpu', 'nofpu'), symbol_lines):
+        return
+
+    # Special case for mips64.
+    if add_to_libc_fallback(directory, ('n32', 'n64'), symbol_lines):
+        return
+
+    raise IOError('No libc.abilist found for: {}'.format(directory))
+
+def move_symbols_1(path, to_move, moved_symbols):
+    """Move SYMBOLS from the abilist file PATH to MOVED_SYMBOLS.
+
+    TO_MOVE must be a set of strings.  MOVED_SYMBOLS is a dictionary.
+
+    """
+    suffix = '.abilist'
+    assert path.endswith('.abilist')
+    library = os.path.basename(path)[:-len(suffix)]
+    placeholder = '__{}_version_placeholder'.format(library)
+
+    new_lines = []
+    changed = False
+
+    old_symbols = read_abilist(path)
+    old_versions = set(versym.version for versym in old_symbols.keys())
+    matching_symbols = dict(e for e in old_symbols.items()
+                            if e[0].symbol in to_move)
+    if matching_symbols:
+        sys.stdout.write('updating {} abilist {}\n'.format(library, path))
+        new_symbols = dict(e for e in old_symbols.items()
+                           if e[0].symbol not in to_move)
+
+        # Add placeholder symbols to prevent symbol versions from
+        # going away completely.
+        new_versions = set(versym.version for versym in new_symbols.keys())
+        for missing_version in old_versions - new_versions:
+            new_symbols[VersionedSymbol(placeholder, missing_version)] = 'F'
+
+        replace_file(path, abilist_lines(new_symbols))
+
+        moved_symbols.update(matching_symbols)
+
+def move_symbols(directory, files, symbols):
+    """Move SYMBOLS from FILES (a list of abilist file names) in DIRECTORY.
+
+    SYMBOLS must be a set of strings.
+
+    """
+    moved_symbols = {}
+    for filename in files:
+        move_symbols_1(os.path.join(directory, filename), symbols,
+                       moved_symbols)
+    if moved_symbols:
+        add_to_libc(directory, moved_symbols)
+
+def get_parser():
+    """Return an argument parser for this module."""
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('--only-linux', action='store_true',
+                        help='Restrict the operation to Linux abilists')
+    parser.add_argument('symbols', help='name of the symbol to move',
+                        nargs='+')
+    return parser
+
+def main(argv):
+    """The main entry point."""
+    parser = get_parser()
+    opts = parser.parse_args(argv)
+    if opts.only_linux:
+        sysdeps = 'sysdeps/unix/sysv/linux'
+    else:
+        sysdeps = 'sysdeps'
+
+    symbols = frozenset(opts.symbols)
+
+    for directory, dirs, files in os.walk(sysdeps):
+        move_symbols(directory, [name for name in files
+                                 if name != 'libc.abilist'
+                                 and name.endswith('.abilist')], symbols)
+
+if __name__ == '__main__':
+    main(sys.argv[1:])