The Tor Browser: tools/rb/fix-linux-stack.pl@97036ab72558 (annotated)

tools/rb/fix-linux-stack.pl@97036ab72558 (annotated)

tools/rb/fix-linux-stack.pl

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rwxr-xr-x

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 #!/usr/bin/perl
 # vim:sw=4:ts=4:et:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 # $Id: fix-linux-stack.pl,v 1.16 2008/05/05 21:51:11 dbaron%dbaron.org Exp $
 #
 # This script uses addr2line (part of binutils) to process the output of
 # nsTraceRefcnt's Linux stack walking code.  This is useful for two
 # things:
 #  (1) Getting line number information out of
 #      |nsTraceRefcnt::WalkTheStack|'s output in debug builds.
 #  (2) Getting function names out of |nsTraceRefcnt::WalkTheStack|'s
 #      output on optimized builds (where it mostly prints UNKNOWN
 #      because only a handful of symbols are exported from component
 #      libraries).
 #
 # Use the script by piping output containing stacks (such as raw stacks
 # or make-tree.pl balance trees) through this script.
 use strict;
 use IPC::Open2;
 use File::Basename;
 # XXX Hard-coded to gdb defaults (works on Fedora).
 my $global_debug_dir = '/usr/lib/debug';
 # We record several things for each file encountered.
 #
 # - {pipe_read}, {pipe_write}: these constitute a bidirectional pipe to an
 #   addr2line process that gives symbol information for a file.
 #
 # - {cache}: this table holds the results of lookups that we've done
 #   previously for (pre-adjustment) addresses, which lets us avoid redundant
 #   calls to addr2line.
 #
 # - {address_adjustment}: addr2line wants offsets relative to the base address
 #   for shared libraries, but it wants addresses including the base address
 #   offset for executables.  This holds the appropriate address adjustment to
 #   add to an offset within file.  See bug 230336.
 #
 my %file_infos;
 sub set_address_adjustment($$) {
     my ($file, $file_info) = @_;
     # find out if it's an executable (as opposed to a shared library)
     my $elftype;
     open(ELFHDR, '-|', 'readelf', '-h', $file);
     while (<ELFHDR>) {
         if (/^\s*Type:\s+(\S+)/) {
             $elftype = $1;
             last;
         }
     }
     close(ELFHDR);
     # If it's an executable, make adjustment the base address.
     # Otherwise, leave it zero.
     my $adjustment = 0;
     if ($elftype eq 'EXEC') {
         open(ELFSECS, '-|', 'readelf', '-S', $file);
         while (<ELFSECS>) {
             if (/^\s*\[\s*\d+\]\s+\.text\s+\w+\s+(\w+)\s+(\w+)\s+/) {
                 # Subtract the .text section's offset within the
                 # file from its base address.
                 $adjustment = hex($1) - hex($2);
                 last;
             }
         }
         close(ELFSECS);
     }
     $file_info->{address_adjustment} = $adjustment;
 }
 # Files sometimes contain a link to a separate object file that contains
 # the debug sections of the binary, removed so that a smaller file can
 # be shipped, but kept separately so that it can be obtained by those
 # who want it.
 # See http://sources.redhat.com/gdb/current/onlinedocs/gdb_16.html#SEC154
 # for documentation of debugging information in separate files.
 # On Fedora distributions, these files can be obtained by installing
 # *-debuginfo RPM packages.
 sub separate_debug_file_for($) {
     my ($file) = @_;
     # We can read the .gnu_debuglink section using either of:
     #   objdump -s --section=.gnu_debuglink $file
     #   readelf -x .gnu_debuglink $file
     # Since readelf prints things backwards on little-endian platforms
     # for some versions only (backwards on Fedora Core 6, forwards on
     # Fedora 7), use objdump.
     # See if there's a .gnu_debuglink section
     my $have_debuglink = 0;
     open(ELFSECS, '-|', 'readelf', '-S', $file);
     while (<ELFSECS>) {
         if (/^\s*\[\s*\d+\]\s+\.gnu_debuglink\s+\w+\s+(\w+)\s+(\w+)\s+/) {
             $have_debuglink = 1;
             last;
         }
     }
     close(ELFSECS);
     return '' unless ($have_debuglink);
     # Determine the endianness of the shared library.
     my $endian = '';
     open(ELFHDR, '-|', 'readelf', '-h', $file);
     while (<ELFHDR>) {
         if (/^\s*Data:\s+.*(little|big) endian.*$/) {
             $endian = $1;
             last;
         }
     }
     close(ELFHDR);
     if ($endian ne 'little' && $endian ne 'big') {
         print STDERR "Warning: could not determine endianness of $file.\n";
         return '';
     }
     # Read the debuglink section as an array of words, in hexidecimal.
     open(DEBUGLINK, '-|', 'objdump', '-s', '--section=.gnu_debuglink', $file);
     my @words;
     while (<DEBUGLINK>) {
         if ($_ =~ /^ [0-9a-f]* ([0-9a-f ]{8}) ([0-9a-f ]{8}) ([0-9a-f ]{8}) ([0-9a-f ]{8}).*/) {
             push @words, $1, $2, $3, $4;
         }
     }
     close(DEBUGLINK);
     while (@words[$#words] eq '        ') {
         pop @words;
     }
     if ($#words < 1) {
         print STDERR "Warning: .gnu_debuglink section in $file too short.\n";
         return '';
     }
     my @chars;
     while ($#words >= 0) {
         my $w = shift @words;
         if ($w =~ /^([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})$/) {
             push @chars, $1, $2, $3, $4;
         } else {
             print STDERR "Warning: malformed objdump output for $file.\n";
             return '';
         }
     }
     my @hash_bytes = map(hex, @chars[$#chars - 3 .. $#chars]);
     $#chars -= 4;
     my $hash;
     if ($endian eq 'little') {
         $hash = ($hash_bytes[3] << 24) | ($hash_bytes[2] << 16) | ($hash_bytes[1] << 8) | $hash_bytes[0];
     } else {
         $hash = ($hash_bytes[0] << 24) | ($hash_bytes[1] << 16) | ($hash_bytes[2] << 8) | $hash_bytes[3];
     }
     # The string ends with a null-terminator and then 0 to three bytes
     # of padding to fill the current 32-bit unit.  (This padding is
     # usually null bytes, but I've seen null-null-H, on Ubuntu x86_64.)
     my $terminator = 1;
     while ($chars[$terminator] ne '00') {
         if ($terminator == $#chars) {
             print STDERR "Warning: missing null terminator in " .
                          ".gnu_debuglink section of $file.\n";
             return '';
         }
         ++$terminator;
     }
     if ($#chars - $terminator > 3) {
         print STDERR "Warning: Excess padding in .gnu_debuglink section " .
                      "of $file.\n";
         return '';
     }
     $#chars = $terminator - 1;
     my $basename = join('', map { chr(hex($_)) } @chars);
     # Now $basename and $hash represent the information in the
     # .gnu_debuglink section.
     #printf STDERR "%x: %s\n", $hash, $basename;
     my @possible_results = (
         dirname($file) . $basename,
         dirname($file) . '.debug/' . $basename,
         $global_debug_dir . dirname($file) . '/' . $basename
     );
     foreach my $result (@possible_results) {
         if (-f $result) {
             # XXX We should check the hash.
             return $result;
         }
     }
     return '';
 }
 sub get_file_info($) {
     my ($file) = @_;
     my $file_info = $file_infos{$file};
     unless (defined $file_info) {
         my $debug_file = separate_debug_file_for($file);
         $debug_file = $file if ($debug_file eq '');
         my $pid = open2($file_info->{pipe_read}, $file_info->{pipe_write},
                         '/usr/bin/addr2line', '-C', '-f', '-e', $debug_file);
         set_address_adjustment($file, $file_info);
         $file_infos{$file} = $file_info;
     }
     return $file_info;
 }
 # Ignore SIGPIPE as a workaround for addr2line crashes in some situations.
 $SIG{PIPE} = 'IGNORE';
 select STDOUT; $| = 1; # make STDOUT unbuffered
 while (<>) {
     my $line = $_;
     if ($line =~ /^([ \|0-9-]*)(.*) ?\[([^ ]*) \+(0x[0-9A-F]{1,8})\](.*)$/) {
         my $before = $1; # allow preservation of balance trees
         my $badsymbol = $2;
         my $file = $3;
         my $address = hex($4);
         my $after = $5; # allow preservation of counts
         if (-f $file) {
             my $file_info = get_file_info($file);
             my $result = $file_info->{cache}->{$address};
             if (not defined $result) {
                 my $address2 = $address + $file_info->{address_adjustment};
                 my $out = $file_info->{pipe_write};
                 my $in = $file_info->{pipe_read};
                 printf {$out} "0x%X\n", $address2;
                 chomp(my $symbol = <$in>);
                 chomp(my $fileandline = <$in>);
                 if (!$symbol || $symbol eq '??') { $symbol = $badsymbol; }
                 if (!$fileandline || $fileandline eq '??:0') {
                     $fileandline = $file;
                 }
                 $result = "$symbol ($fileandline)";
                 $file_info->{cache}->{$address} = $result;
             }
             print "$before$result$after\n";
         } else {
             print STDERR "Warning: File \"$file\" does not exist.\n";
             print $line;
         }
     } else {
         print $line;
     }
 }

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tools/rb/fix-linux-stack.pl@97036ab72558 (annotated)

tools/rb/fix-linux-stack.pl