conform/linknamespace.pl

   1 #!/usr/bin/perl
   2
   3 # Check that use of symbols declared in a given header does not result
   4 # in any symbols being brought in that are not reserved with external
   5 # linkage for the given standard.
   6
   7 # Copyright (C) 2014-2017 Free Software Foundation, Inc.
   8 # This file is part of the GNU C Library.
   9
  10 # The GNU C Library is free software; you can redistribute it and/or
  11 # modify it under the terms of the GNU Lesser General Public
  12 # License as published by the Free Software Foundation; either
  13 # version 2.1 of the License, or (at your option) any later version.
  14
  15 # The GNU C Library is distributed in the hope that it will be useful,
  16 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  18 # Lesser General Public License for more details.
  19
  20 # You should have received a copy of the GNU Lesser General Public
  21 # License along with the GNU C Library; if not, see
  22 # <http://www.gnu.org/licenses/>.
  23
  24 use GlibcConform;
  25 use Getopt::Long;
  26
  27 GetOptions ('header=s' => \$header, 'standard=s' => \$standard,
  28             'flags=s' => \$flags, 'cc=s' => \$CC, 'tmpdir=s' => \$tmpdir,
  29             'stdsyms=s' => \$stdsyms_file, 'libsyms=s' => \$libsyms_file,
  30             'readelf=s' => \$READELF);
  31
  32 # Load the list of symbols that are OK.
  33 %stdsyms = ();
  34 open (STDSYMS, "<$stdsyms_file") || die ("open $stdsyms_file: $!\n");
  35 while (<STDSYMS>) {
  36   chomp;
  37   $stdsyms{$_} = 1;
  38 }
  39 close (STDSYMS) || die ("close $stdsyms_file: $!\n");
  40
  41 # The following whitelisted symbols are also allowed for now.
  42 #
  43 # * Bug 17576: stdin, stdout, stderr only reserved with external
  44 # linkage when stdio.h included (and possibly not then), not
  45 # generally.
  46 #
  47 # * Bug 18442: re_syntax_options wrongly brought in by regcomp and
  48 # used by re_comp.
  49 #
  50 @whitelist = qw(stdin stdout stderr re_syntax_options);
  51 foreach my $sym (@whitelist) {
  52   $stdsyms{$sym} = 1;
  53 }
  54
  55 # Return information about GLOBAL and WEAK symbols listed in readelf
  56 # -s output.
  57 sub list_syms {
  58   my ($syms_file) = @_;
  59   open (SYMS, "<$syms_file") || die ("open $syms_file: $!\n");
  60   my ($file) = $syms_file;
  61   my (@ret) = ();
  62   while (<SYMS>) {
  63     chomp;
  64     if (/^File: (.*)/) {
  65       $file = $1;
  66       $file =~ s|^.*/||;
  67       next;
  68     }
  69     s/^\s*//;
  70     # Architecture-specific st_other bits appear inside [] and disrupt
  71     # the format of readelf output.
  72     s/\[.*?\]//;
  73     my (@fields) = split (/\s+/, $_);
  74     if (@fields < 8) {
  75       next;
  76     }
  77     my ($bind) = $fields[4];
  78     my ($ndx) = $fields[6];
  79     my ($sym) = $fields[7];
  80     if ($bind ne "GLOBAL" && $bind ne "WEAK") {
  81       next;
  82     }
  83     if ($sym !~ /^\w+$/) {
  84       next;
  85     }
  86     push (@ret, [$file, $sym, $bind, $ndx ne "UND"]);
  87   }
  88   close (SYMS) || die ("close $syms_file: $!\n");
  89   return @ret;
  90 }
  91
  92 # Load information about GLOBAL and WEAK symbols defined or used in
  93 # the standard libraries.
  94 # Symbols from a given object, except for weak defined symbols.
  95 %seen_syms = ();
  96 # Strong undefined symbols from a given object.
  97 %strong_undef_syms = ();
  98 # Objects defining a given symbol (strongly or weakly).
  99 %sym_objs = ();
 100 @sym_data = list_syms ($libsyms_file);
 101 foreach my $sym (@sym_data) {
 102   my ($file, $name, $bind, $defined) = @$sym;
 103   if ($defined) {
 104     if (!defined ($sym_objs{$name})) {
 105       $sym_objs{$name} = [];
 106     }
 107     push (@{$sym_objs{$name}}, $file);
 108   }
 109   if ($bind eq "GLOBAL" || !$defined) {
 110     if (!defined ($seen_syms{$file})) {
 111       $seen_syms{$file} = [];
 112     }
 113     push (@{$seen_syms{$file}}, $name);
 114   }
 115   if ($bind eq "GLOBAL" && !$defined) {
 116     if (!defined ($strong_undef_syms{$file})) {
 117       $strong_undef_syms{$file} = [];
 118     }
 119     push (@{$strong_undef_syms{$file}}, $name);
 120   }
 121 }
 122
 123 # Determine what ELF-level symbols are brought in by use of C-level
 124 # symbols declared in the given header.
 125 #
 126 # The rules followed are heuristic and so may produce false positives
 127 # and false negatives.
 128 #
 129 # * All undefined symbols are considered of signficance, but it is
 130 # possible that (a) any standard library definition is weak, so can be
 131 # overridden by the user's definition, and (b) the symbol is only used
 132 # conditionally and not if the program is limited to standard
 133 # functionality.
 134 #
 135 # * If a symbol reference is only brought in by the user using a data
 136 # symbol rather than a function from the standard library, this will
 137 # not be detected.
 138 #
 139 # * If a symbol reference is only brought in by crt*.o or libgcc, this
 140 # will not be detected.
 141 #
 142 # * If a symbol reference is only brought in through __builtin_foo in
 143 # a standard macro being compiled to call foo, this will not be
 144 # detected.
 145 #
 146 # * Header inclusions should be compiled several times with different
 147 # options such as -O2, -D_FORTIFY_SOURCE and -D_FILE_OFFSET_BITS=64 to
 148 # find out what symbols are undefined from such a compilation; this is
 149 # not yet implemented.
 150 #
 151 # * This script finds symbols referenced through use of macros on the
 152 # basis that if a macro calls an internal function, that function must
 153 # also be declared in the header.  However, the header might also
 154 # declare implementation-namespace functions that are not called by
 155 # any standard macro in the header, resulting in false positives for
 156 # any symbols brought in only through use of those
 157 # implementation-namespace functions.
 158 #
 159 # * Namespace issues can apply for dynamic linking as well as static
 160 # linking, when a call is from one shared library to another or uses a
 161 # PLT entry for a call within a shared library; such issues are only
 162 # detected by this script if the same namespace issue applies for
 163 # static linking.
 164
 165 @c_syms = list_exported_functions ("$CC $flags", $standard, $header, $tmpdir);
 166 $cincfile = "$tmpdir/undef-$$.c";
 167 $cincfile_o = "$tmpdir/undef-$$.o";
 168 $cincfile_sym = "$tmpdir/undef-$$.sym";
 169 open (CINCFILE, ">$cincfile") || die ("open $cincfile: $!\n");
 170 print CINCFILE "#include <$header>\n";
 171 foreach my $sym (sort @c_syms) {
 172   print CINCFILE "void *__glibc_test_$sym = (void *) &$sym;\n";
 173 }
 174 close CINCFILE || die ("close $cincfile: $!\n");
 175 system ("$CC $flags -D_ISOMAC $CFLAGS{$standard} -c $cincfile -o $cincfile_o")
 176   && die ("compiling failed\n");
 177 system ("LC_ALL=C $READELF -W -s $cincfile_o > $cincfile_sym")
 178   && die ("readelf failed\n");
 179 @elf_syms = list_syms ($cincfile_sym);
 180 unlink ($cincfile) || die ("unlink $cincfile: $!\n");
 181 unlink ($cincfile_o) || die ("unlink $cincfile_o: $!\n");
 182 unlink ($cincfile_sym) || die ("unlink $cincfile_sym: $!\n");
 183
 184 %seen_where = ();
 185 %files_seen = ();
 186 %all_undef = ();
 187 %current_undef = ();
 188 foreach my $sym (@elf_syms) {
 189   my ($file, $name, $bind, $defined) = @$sym;
 190   if ($bind eq "GLOBAL" && !$defined) {
 191     $seen_where{$name} = "[initial] $name";
 192     $all_undef{$name} = "[initial] $name";
 193     $current_undef{$name} = "[initial] $name";
 194   }
 195 }
 196
 197 while (%current_undef) {
 198   %new_undef = ();
 199   foreach my $sym (sort keys %current_undef) {
 200     foreach my $file (@{$sym_objs{$sym}}) {
 201       if (defined ($files_seen{$file})) {
 202         next;
 203       }
 204       $files_seen{$file} = 1;
 205       foreach my $ssym (@{$seen_syms{$file}}) {
 206         if (!defined ($seen_where{$ssym})) {
 207           $seen_where{$ssym} = "$current_undef{$sym} -> [$file] $ssym";
 208         }
 209       }
 210       foreach my $usym (@{$strong_undef_syms{$file}}) {
 211         if (!defined ($all_undef{$usym})) {
 212           $all_undef{$usym} = "$current_undef{$sym} -> [$file] $usym";
 213           $new_undef{$usym} = "$current_undef{$sym} -> [$file] $usym";
 214         }
 215       }
 216     }
 217   }
 218   %current_undef = %new_undef;
 219 }
 220
 221 $ret = 0;
 222 foreach my $sym (sort keys %seen_where) {
 223   if ($sym =~ /^_/) {
 224     next;
 225   }
 226   if (defined ($stdsyms{$sym})) {
 227     next;
 228   }
 229   print "$seen_where{$sym}\n";
 230   $ret = 1;
 231 }
 232
 233 exit $ret;