contrib: Add unused_functions.py script

For a set of object-files, determine symbols that are
 - public but should be static

2018-10-04  Bernhard Reutner-Fischer  <aldot@gcc.gnu.org>

	* unused_functions.py: New file.

From-SVN: r264837

contrib/ChangeLog

+2018-10-04  Bernhard Reutner-Fischer  <aldot@gcc.gnu.org>
+
+	* unused_functions.py: New file.
+
 2018-09-25  Martin Liska  <mliska@suse.cz>
 
 	* filter-rtags-warnings.py: New file.

contrib/unused_functions.py

+#!/usr/bin/env python
+#
+# Copyright (c) 2018 Free Software Foundation
+# Contributed by Bernhard Reutner-Fischer <aldot@gcc.gnu.org>
+# Inspired by bloat-o-meter from busybox.
+
+# This software may be used and distributed according to the terms and
+# conditions of the GNU General Public License as published by the Free
+# Software Foundation.
+
+# For a set of object-files, determine symbols that are
+#  - public but should be static
+
+# Examples:
+# unused_functions.py ./gcc/fortran
+# unused_functions.py gcc/c  gcc/c-family/ gcc/*-c.o | grep -v "'gt_"
+# unused_functions.py gcc/cp gcc/c-family/ gcc/*-c.o | grep -v "'gt_"
+
+import sys, os
+
+def usage():
+    sys.stderr.write("usage: %s [dirs | files] [-- <readelf options>]\n"
+                        % sys.argv[0])
+    sys.exit(1)
+
+(odir, sym_args) = (set(), "")
+
+for i in range(1, len(sys.argv)):
+    f = sys.argv[i]
+    if f == "--": # sym_args
+        sym_args = " ".join(sys.argv[i + 1:])
+        break
+    if not os.path.exists(f):
+        sys.stderr.write("Error: No such file or directory '%s'\n" % f)
+        usage()
+    else:
+        odir.add(f)
+
+def get_symbols(file):
+    syms = {}
+    for l in os.popen("readelf -W -s %s %s | c++filt" % (sym_args, file)).readlines():
+        l = l.strip()
+        if not (len(l) and l[0].isdigit() and len(l.split()) == 8):
+            continue
+        num, value, size, typ, bind, vis, ndx, name = l.split()
+        if typ == 'SECTION' or typ == 'FILE': continue
+        # I don't think we have many aliases in gcc, re-instate the addr
+        # lut otherwise.
+        if vis != "DEFAULT": continue
+        #value = int(value, 16)
+        #size = int(size, 16) if size.startswith('0x') else int(size)
+        defined = ndx != "UND"
+        globl = bind == "GLOBAL"
+        # c++ RID_FUNCTION_NAME dance. FORNOW: Handled as local use
+        # Is that correct?
+        if name.endswith("::__FUNCTION__") and typ == "OBJECT":
+            name = name[0:(len(name) - len("::__FUNCTION__"))]
+            if defined: defined = False
+        if defined and not globl: continue
+        syms.setdefault(name, {})
+        syms[name][["use","def"][defined]] = True
+        syms[name][["local","global"][globl]] = True
+    # Note: we could filter out e.g. debug_* symbols by looking for
+    # value in the debug_macro sections.
+    return syms
+
+(oprog, nprog) = ({}, {})
+
+def walker(paths):
+    prog = {}
+    for path in paths:
+        if os.path.isdir(path):
+            for r, dirs, files in os.walk(path):
+                for f in files:
+                    # TODO: maybe extract .a to a tmpdir and walk that, too
+                    # maybe /there/foolib.a(file.o) as name?
+                    if not f.endswith(".o"): continue
+                    p = os.path.join(r, f)
+                    prog[os.path.normpath(p)] = get_symbols(p)
+                for d in dirs:
+                    tem = prog.copy()
+                    tem.update(walker([os.path.join(r, d)]))
+                    prog = tem
+        else:
+            prog[os.path.normpath(path)] = get_symbols(path)
+    return prog
+
+def resolve(prog):
+    x = prog.keys()
+    use = set()
+    # for each unique pair of different files
+    for (f, g) in ((f,g) for f in x for g in x if f != g):
+        refs = set()
+        # for each defined symbol
+        for s in (s for s in prog[f] if prog[f][s].get("def") and s in prog[g]):
+            if prog[g][s].get("use"):
+                refs.add(s)
+        for s in refs:
+            # Prune externally referenced symbols as speed optimization only
+            for i in (i for i in x if s in prog[i]): del prog[i][s]
+        use |= refs
+    return use
+
+oprog = walker(odir)
+oused = resolve(oprog)
+for (i,s) in ((i,s) for i in oprog.keys() for s in oprog[i] if oprog[i][s]):
+    if oprog[i][s].get("def") and not oprog[i][s].get("use"):
+        print("%s: Symbol '%s' declared extern but never referenced externally"
+            % (i,s))
+
+