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698 lines
18 KiB
Perl
Executable File
698 lines
18 KiB
Perl
Executable File
#!/usr/bin/perl
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# File: guest-gdb
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#
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# Purpose: Wraps a GNU Debugger instance around a program. Watches for
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# invocations of a gdb() function to handle gdb commands from the program.
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# Reports information about local variables when signals are detected.
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#
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# Usage: guest-gdb [executable]
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#
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# If [executable] is omitted, it will default to `prog`. Don't forget to
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# compile with -g for debugging symbols.
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# The DEBUG environment variable can be set to an integer value to enable
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# internal debugging output. Set it to 1 for minimal debugging; to 2 to
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# also dump the parsed GDB/MI data structures.
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# SPDX-FileCopyrightText: 2022 Pragmatic Software <pragma78@gmail.com>
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# SPDX-License-Identifier: MIT
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use 5.020;
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use warnings;
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use strict;
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use feature qw(signatures);
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no warnings qw(experimental::signatures);
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use IPC::Open2;
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use JSON::XS;
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use Data::Dumper;
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use Encode qw(decode encode);
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# set debug flag from DEBUG env or here
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my $debug = $ENV{DEBUG} // 0;
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# output from gdb will be prefixed with GDB_PREFIX and suffixed with GDB_SUFFIX.
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# e.g., to wrap gdb output with <>'s set GDB_PREFIX to "<" and GDB_SUFFIX to ">".
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use constant {
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GDB_PREFIX => "\n",
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GDB_SUFFIX => "\n\n",
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};
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# files to read stdin and write stdout
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use constant {
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INPUT_FILENAME => '.input',
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OUTPUT_FILENAME => '.output',
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};
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# GDB/MI message types
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use constant {
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STATUS => '+',
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EXEC => '*',
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NOTIFY => '=',
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CONSOLE => '~',
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TARGET => '@',
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LOG => '&',
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RESULT => '^',
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};
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# send a command to gdb
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sub gdb_send($in, $command) {
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print STDERR "-> $command\n" if $debug;
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print $in "$command\n";
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}
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# read a line from gdb
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sub gdb_read($out) {
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my $line;
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while ($line = <$out>) {
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chomp $line;
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print STDERR "<- [$line]\n" if $debug;
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next if $line eq '(gdb) '; # ignore gdb prompt
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last;
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}
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return undef if not defined $line;
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return parse_gdbmi_output($line);
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}
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# send a command to gdb and return all ~console and ^result output
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sub gdb_send_and_read_console($context, $command, $report_error = 1) {
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gdb_send($context->{gdb_input}, $command);
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my $gdb = $context->{gdb_output};
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my @console;
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my $output;
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while ($output = gdb_read_console($gdb)) {
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push @console, $output;
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last if $output->{_type} eq RESULT;
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}
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if ($report_error && $output->{_type} eq RESULT && $output->{_class} eq 'error') {
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print_gdb_output($context, $output->{msg});
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}
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return \@console;
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}
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# send a command to gdb and return only the ^result output
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sub gdb_send_and_read_result($context, $command, $report_error = 1) {
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gdb_send($context->{gdb_input}, $command);
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my $gdb = $context->{gdb_output};
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my $output;
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while ($output = gdb_read($gdb)) {
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last if $output->{_type} eq RESULT;
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}
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if ($report_error && $output->{_class} eq 'error') {
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print_gdb_output($context, $output->{msg});
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}
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return $output;
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}
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# alias to send_and_read_result
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*gdb_send_and_discard = \&gdb_send_and_read_result;
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# read line from gdb, discarding types other than ~console or ^result
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sub gdb_read_console($out) {
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my $output;
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while ($output = gdb_read($out)) {
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last if $output->{_type} eq RESULT;
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last if $output->{_type} eq CONSOLE;
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}
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return $output;
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}
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# read and discard all output until ^result is reached
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sub gdb_read_result($out) {
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my $output;
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while ($output = gdb_read($out)) {
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last if $output->{_type} eq RESULT;
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}
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return $output;
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}
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# convert gdb/mi text to hashtable, converting to JSON first if necessary
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sub gdbmi_to_hash($text, $makejson = 1) {
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# convert to JSON first if necessary (gdb/mi is nearly JSON already!)
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$text =~ s/"(?:[^"\\]|\\.)*"(*SKIP)(*F)|([\w-]+)=/"$1":/g if $makejson;
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# decode gdb octal escapes
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# (sometimes \\123, othertimes \123 and I can't be arsed to investigate
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# when and why the backslashes double up)
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$text =~ s/\\+(\d{3})/$1 >= 0x20 ? chr oct $1 : "\\\\$1"/ge;
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# escape malformed unicode
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my $octets = decode('UTF-8', $text, sub { sprintf '\\\\x%02X', shift });
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$text = encode('UTF-8', $octets, Encode::FB_CROAK);
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# escape invalid JSON characters
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$text =~ s/([\x10-\x1f])/sprintf '\\\\x%02X', ord $1/ge;
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# return hashtable decoded from json
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my $result = eval { decode_json("{$text}") };
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if ($@) {
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print "Error parsing GDB/MI: $@ (input: $text)\n";
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exit 1;
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}
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return $result;
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}
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sub parse_gdbmi_output($line) {
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my ($type, $text) = $line =~ /^\d*(.)(.*)/;
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my $class = 'none';
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my $makejson = 0;
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if ($type =~ /[+*=]/) {
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($class, $text) = split /,/, $text, 2;
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$makejson = 1 if length $text;
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} elsif ($type eq RESULT) {
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($class, $text) = split /,/, $text, 2;
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$text //= '';
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$makejson = 1 if length $text;
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} else {
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$text = "\"_text\":$text";
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}
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my $output = gdbmi_to_hash($text, $makejson);
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if (exists $output->{_text}) {
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chomp $output->{_text};
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}
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$output->{_type} = $type;
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$output->{_class} = $class;
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print STDERR Dumper($output), "\n" if $debug >= 2;
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return $output;
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}
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# get local variables at current frame
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sub get_locals($context) {
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# use `info locals` gdb command
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my $console = gdb_send_and_read_console($context, "info locals");
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my @locals;
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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if ($output->{_text} =~ /([^=]+)\s+=\s+(.*)/) {
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push @locals, [$1, $2];
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}
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}
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return \@locals;
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}
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# compare two lists of locals and returns list containing just the
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# newly modified locals
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sub compare_locals($old, $new) {
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# build hashtable of left-side locals for easier access
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my %ht;
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foreach my $local (@$old) {
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my ($ident, $value) = @$local;
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$ht{$ident} = $value;
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}
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# check for modified locals and add to modified list
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my @modified;
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foreach my $local (@$new) {
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my ($ident, $value) = @$local;
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if (!exists $ht{$ident} || $ht{$ident} ne $value) {
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push @modified, [$ident, $value];
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}
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}
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return \@modified;
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}
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sub locals_to_string($locals) {
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my @strings;
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foreach my $local (@$locals) {
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my ($ident, $value) = @$local;
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push @strings, "$ident = $value";
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}
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return join '; ', @strings;
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}
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sub args_to_string($args) {
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my @strings;
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foreach my $arg (@$args) {
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push @strings, "$arg->{name}=$arg->{value}";
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}
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return join ', ', @strings;
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}
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# determine on which line numbers the main() function begins and ends
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sub get_main_start_end($context) {
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gdb_send_and_discard($context, 'set listsize unlimited');
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my ($start, $end);
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# use `info functions` to find where main starts
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my $console = gdb_send_and_read_console($context, 'info functions -q ^main$');
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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($start) = $output->{_text} =~ /^(\d+)/;
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}
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$console = gdb_send_and_read_console($context, 'list main');
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# gdb shows extra context surrounding main, so we have to parse the output
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# and count the braces to find the true end of main()
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my $braces = 0;
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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# we have already found end; don't parse output
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last if $end;
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my ($line, $code) = split /\t/, $output->{_text};
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# this line isn't part of main() yet
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next if $line < $start;
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# blank out contents of string and char literals so we don't count
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# any braces within
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$code =~ s/(?:\"((?:\\\"|(?!\").)*)\")/'"' . ('-' x length $1) . '"'/ge;
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$code =~ s/(?:\'((?:\\\'|(?!\').)*)\')/"'" . ('-' x length $1) . "'"/ge;
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my @chars = split //, $code;
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foreach my $char (@chars) {
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if ($char eq '{') {
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$braces++;
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} elsif ($char eq '}') {
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$braces--;
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if ($braces == 0) {
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$end = $line - 1;
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last;
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}
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}
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}
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}
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return ($start, $end);
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}
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sub get_backtrace($context) {
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my $console = gdb_send_and_read_console($context, "bt");
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my @backtrace;
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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$output->{_text} =~ /in (\w+) (.*) at/;
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push @backtrace, { func => $1, args => $2 };
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}
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return \@backtrace;
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}
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# returns the source line at a given line number
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sub get_lineno($context, $lineno) {
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my $console = gdb_send_and_read_console($context, "list $lineno,$lineno", 0);
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my $line;
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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($line) = $output->{_text} =~ /\t\s+(.*)/;
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}
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return $line;
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}
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sub handle_breakpoint_hit($context, $data) {
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if ($data->{frame}->{func} eq 'main') {
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if ($data->{frame}->{line} == $context->{main_end}) {
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$context->{locals_end} = get_locals($context);
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}
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}
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elsif ($data->{frame}->{func} eq 'gdb') {
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my $command = $data->{frame}->{args}->[0]->{value};;
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# strip gdb junk from command
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$command =~ s/^.*?"//;
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$command =~ s/"$//;
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dispatch_user_command($context, $command);
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}
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gdb_send_and_discard($context, "cont");
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}
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# gdb commands invoked by end-users
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sub dispatch_user_command($context, $command) {
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state %commands = (
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'ptype' => \&cmd_ptype,
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'whatis' => \&cmd_whatis,
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'print' => \&cmd_print,
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'dump' => \&cmd_print,
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# special PBot command
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'print_last_statement' => \&cmd_print_last_statement,
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);
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$command = unescape($command);
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# move out of gdb() function to caller
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gdb_send_and_discard($context, "up");
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my ($cmd, $args) = split /\s+/, $command, 2;
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if (not exists $commands{$cmd}) {
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cmd_gdb($context, $command);
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} else {
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$commands{$cmd}->($context, $args);
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}
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}
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sub cmd_gdb($context, $command) {
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my $console = gdb_send_and_read_console($context, "$command");
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my $text = '';
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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$text .= "$output->{_text}\n";
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}
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print_gdb_output($context, $text);
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}
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sub cmd_ptype($context, $args) {
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my $console = gdb_send_and_read_console($context, "ptype $args");
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my $text = '';
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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if ($output->{_text} =~ /type\s*=\s*(.*)/) {
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$text .= "$args = $1"
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} else {
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$output->{_text} =~ s/^\s+//;
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$text .= " $output->{_text}";
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}
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}
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print_gdb_output($context, $text);
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}
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sub cmd_whatis($context, $args) {
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my $console = gdb_send_and_read_console($context, "whatis $args");
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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if ($output->{_text} =~ /type\s*=\s*(.*)/) {
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print_gdb_output($context, "$args = $1");
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}
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}
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}
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sub cmd_print($context, $args) {
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my $console = gdb_send_and_read_console($context, "print $args");
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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if ($output->{_text} =~ /^\$\d+\s*=\s*(.*)/) {
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print_gdb_output($context, "$args = $1");
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}
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}
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}
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sub cmd_print_last_statement($context, $args) {
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# invoke the last statement
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my $console = gdb_send_and_read_console($context, "print $args");
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# don't print last statement if there was program output
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return if -s OUTPUT_FILENAME;
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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if ($output->{_text} =~ /^\$\d+\s*=\s*(.*)/) {
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print_gdb_output($context, "no output: $args = $1");
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}
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}
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}
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sub handle_program_exit($context, $data) {
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if (not -s OUTPUT_FILENAME) { # -s gets size of file
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my $locals = locals_to_string($context->{locals_end});
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if (length $locals) {
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print_gdb_output($context, "no output: $locals");
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}
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}
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if (exists $data->{'exit-code'} && $data->{'exit-code'} != 0) {
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$context->{'exit-code'} = oct $data->{'exit-code'};
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}
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_exit($context);
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}
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sub handle_program_signal($context, $data) {
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my $locals = locals_to_string(get_locals($context));
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my $args = args_to_string($data->{frame}->{args});
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my $text = "Program received signal $data->{'signal-name'}, $data->{'signal-meaning'} ";
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$text .= "in $data->{frame}->{func} ($args) ";
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my $line;
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if (exists $data->{frame}->{line}) {
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if ($line = get_lineno($context, $data->{frame}->{line})) {
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$text .= "at statement: $line ";
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}
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}
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my $backtrace = get_backtrace($context);
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shift @$backtrace; # remove current frame
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foreach my $trace (@$backtrace) {
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my $console = gdb_send_and_read_console($context, "up");
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foreach my $output (@$console) {
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last if $output->{_type} eq RESULT;
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if ($output->{_text} =~ /^\d+\t\s+(.*)/) {
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$line = $1;
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}
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}
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$text .= "called by $trace->{func} $trace->{args} " if $trace->{func};
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$text .= "at statement: $line " if $line;
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}
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if (length $locals) {
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$text .= "<local variables: $locals>"
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} else {
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$text =~ s/\s+$//;
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}
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print_gdb_output($context, $text);
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_exit($context);
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}
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sub unescape($text) {
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state %unescape = (
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"\\n" => "\n",
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"\\t" => "\t",
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"\\\\" => "\\",
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"\\\"" => '"',
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);
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$text =~ s/(\\n|\\t|\\\\|\\")/$unescape{$1}/g;
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return $text;
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}
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# dispatch output from gdb commands to handlers
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sub dispatch_gdbmi_output($context, $output) {
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state %dispatch = (
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STATUS , \&handle_status_async_output,
|
||
EXEC , \&handle_exec_async_output,
|
||
NOTIFY , \&handle_notify_async_output,
|
||
CONSOLE , \&handle_console_stream_output,
|
||
TARGET , \&handle_target_stream_output,
|
||
LOG , \&handle_log_stream_output,
|
||
RESULT , \&handle_result_output,
|
||
);
|
||
|
||
$dispatch{$output->{_type}}->($context, $output);
|
||
}
|
||
|
||
# (+) status-async-output contains on-going status information about the progress
|
||
# of a slow operation. It can be discarded.
|
||
sub handle_status_async_output($context, $output) {
|
||
}
|
||
|
||
# (*) exec-async-output contains asynchronous state change on the target (stopped,
|
||
# started, disappeared).
|
||
sub handle_exec_async_output($context, $output) {
|
||
if ($output->{_class} eq 'stopped') {
|
||
my $reason = $output->{reason};
|
||
|
||
if ($reason eq 'breakpoint-hit') {
|
||
handle_breakpoint_hit($context, $output);
|
||
}
|
||
elsif ($reason eq 'exited-normally' || $reason eq 'exited') {
|
||
handle_program_exit($context, $output);
|
||
}
|
||
elsif ($reason eq 'signal-received') {
|
||
handle_program_signal($context, $output);
|
||
}
|
||
}
|
||
}
|
||
|
||
# (=) notify-async-output contains supplementary information that the client should
|
||
# handle (e.g., a new breakpoint information).
|
||
sub handle_notify_async_output($context, $output) {
|
||
}
|
||
|
||
# (~) console-stream-output is output that should be displayed as is in the console.
|
||
# It is the textual response to a CLI command.
|
||
sub handle_console_stream_output($context, $output) {
|
||
if ($output->{_text} =~ /^Reading symbols/) {
|
||
perform_preamble($context);
|
||
run_program($context);
|
||
}
|
||
}
|
||
|
||
# (@) target-stream-output is the output produced by the target program.
|
||
sub handle_target_stream_output($context, $output) {
|
||
}
|
||
|
||
# (&) log-stream-output is output text coming from GDB’s internals, for instance
|
||
# messages that should be displayed as part of an error log.
|
||
sub handle_log_stream_output($context, $output) {
|
||
}
|
||
|
||
# (^) result-output "done" | "running" | "connected" | "error" | "exit"
|
||
sub handle_result_output($context, $output) {
|
||
}
|
||
|
||
sub start_timeout($context, $timeout) {
|
||
$SIG{ALRM} = sub {
|
||
print_prog_output($context, "[gdb time-out]\n");
|
||
_exit($context);
|
||
};
|
||
alarm $timeout;
|
||
}
|
||
|
||
sub _exit($context) {
|
||
close $context->{prog_output};
|
||
|
||
open my $fh, '<', OUTPUT_FILENAME or die "could not open ".OUTPUT_FILENAME." for read: $!\n";
|
||
my $output = do { local $/; <$fh> };
|
||
close $fh;
|
||
|
||
print STDOUT "$output";
|
||
|
||
exit ($context->{'exit-code'} // 0);
|
||
}
|
||
|
||
# send text to OUTPUT_FILENAME file
|
||
sub print_prog_output($context, $text) {
|
||
print { $context->{prog_output} } $text;
|
||
$context->{prog_output}->flush();
|
||
}
|
||
|
||
# send gdb output to OUTPUT_FILENAME file, wrapped with prefix and suffix
|
||
sub print_gdb_output($context, $text) {
|
||
print { $context->{prog_output} } GDB_PREFIX . $text . GDB_SUFFIX;
|
||
$context->{prog_output}->flush();
|
||
}
|
||
|
||
sub perform_preamble($context) {
|
||
gdb_send_and_discard($context, "set charset UTF-8");
|
||
gdb_send_and_discard($context, "set print sevenbit-strings on");
|
||
|
||
# get start and end line numbers for main() function
|
||
my ($start, $end) = get_main_start_end($context);
|
||
|
||
$context->{main_start} = $start;
|
||
$context->{main_end} = $end;
|
||
|
||
# break on main start and end so we can get locals
|
||
gdb_send_and_discard($context, "break $start");
|
||
gdb_send_and_discard($context, "break $end");
|
||
|
||
# break on gdb() function so we can pass along user-submitted gdb commands
|
||
gdb_send_and_discard($context, "break gdb");
|
||
gdb_send_and_discard($context, "set print null-stop on");
|
||
}
|
||
|
||
sub shellquote_args_to_string(@args) {
|
||
my $string = '';
|
||
|
||
foreach my $arg (@args) {
|
||
$arg =~ s/'/'"'"'/g;
|
||
$string .= "'$arg' ";
|
||
}
|
||
|
||
return $string;
|
||
}
|
||
|
||
sub run_program($context) {
|
||
my $cmdline_args = shellquote_args_to_string(@ARGV);
|
||
gdb_send($context->{gdb_input}, "run $cmdline_args < ".INPUT_FILENAME." >> ".OUTPUT_FILENAME);
|
||
}
|
||
|
||
sub main {
|
||
# first command-line argument can override file to debug
|
||
my $prog = shift @ARGV // './prog';
|
||
|
||
# start gdb and grab references to its input and output streams
|
||
open2(my $out, my $in, "LIBC_FATAL_STDERR=1 MALLOC_CHECK_=1 gdb -i mi3 -q -nx $prog");
|
||
|
||
my $context = {
|
||
gdb_output => $out, # gdb output stream
|
||
gdb_input => $in, # gdb input stream
|
||
};
|
||
|
||
# open OUTPUT_FILENAME file to send gdb output
|
||
unlink OUTPUT_FILENAME;
|
||
open($context->{prog_output}, '>>:encoding(UTF-8)', OUTPUT_FILENAME) or die "Could not open ".OUTPUT_FILENAME." for append: $!";
|
||
|
||
# time-out after a few seconds
|
||
start_timeout($context, 8);
|
||
|
||
# handle gdb output
|
||
while (my $output = gdb_read($out)) {
|
||
dispatch_gdbmi_output($context, $output);
|
||
}
|
||
}
|
||
|
||
main();
|