dh_dwz

#!/usr/bin/perl

=head1 NAME

dh_dwz - optimize DWARF debug information in ELF binaries via dwz

=cut

use strict;
use warnings;
use File::Find;
use Debian::Debhelper::Dh_Lib;

our $VERSION = DH_BUILTIN_VERSION;

=head1 SYNOPSIS

B<dh_dwz> [S<I<debhelper options>>] [B<-X>I<item>] [S<B<--> I<params>>]

=head1 DESCRIPTION

B<dh_dwz> is a debhelper program that will optimize the (uncompressed)
size of the DWARF debug information in ELF binaries.  It does so by
running L<dwz(1)> on all the ELF binaries in the package.

=head1 OPTIONS

=over 4

=item B<--dwz-multifile>, B<--no-dwz-multifile>

Whether L<dwz(1)> should generate a I<multifile> from the ELF binaries
in the same package.  When enabled, if a package ships at least 2 ELF
binaries, B<dh_dwz> will instruct L<dwz(1)> to generate a multifile
for the package.

By default, B<dh_dwz> will attempt to create a multifile but will
continue without if L<dwz(1)> does not create one (but succeeds anyway).
This commonly happens when the debug files do not contain debug
symbols (e.g. a missing -g to the compiler) or when the debug
symbols are compressed (see Debian bug #931891).  If B<--dwz-multifile>
is passed, then B<dh_dwz> will abort with an error if L<dwz(1)> does
not create a multifile.

Note this options may not work if a package contains more ELF binaries
than can fit on a single command line.  If this becomes a problem,
please pass B<--no-dwz-multifile> to work around the issue.

The generated multifile will be compressed with B<objcopy
--compress-debug-sections>.

Note for B<udeb> packages: B<dh_dwz> will never generate multifiles
for B<udeb> packages.  It will still use B<dwz> to reduce the
file size of debug files if it finds any.

=item B<-X>I<item>, B<--exclude=>I<item>

Exclude files that contain I<item> anywhere in their filename from being
stripped. You may use this option multiple times to build up a list of
things to exclude.

=item B<--> I<params>

Pass I<params> to L<dwz(1)> when it processes ELF binaries.  This is
mostly useful for setting memory related parameters (e.g. -l and -L).

=back

=head1 NOTES

If the B<DEB_BUILD_OPTIONS> environment variable contains B<nostrip>,
nothing will be stripped, in accordance with Debian policy (section
10.1 "Binaries").

While this tool technically does not remove debug information from
binaries, it is still skipped when the B<DEB_BUILD_OPTIONS>
environment variable contains B<nostrip>.  This is because B<nostrip>
is often used to optimize build times (e.g. for "build and
test"-cycles) rather than optimizing for size.

=cut

my $create_multifile = 'auto';

init(options => {
	'dwz-multifile!' => \$create_multifile,
});

# This variable can be used to turn off stripping (see Policy).
exit 0 if get_buildoption('nostrip');

my @elf_files;

sub testfile {
	my $fn = $_;
	return if -l $fn; # Always skip symlinks.

	# See if we were asked to exclude this file.
	# Note that we have to test on the full filename, including directory.
	if (excludefile($fn)) {
		$File::Find::prune = 1 if -d _;
		return;
	}
	return if -d _;
	# Do not process output files from dwz
	return if index($fn, '/debug/.dwz/') > -1;
	if (is_so_or_exec_elf_file($fn)) {
		push(@elf_files, $fn);
	}
	return;
}

for my $package (@{$dh{DOPACKAGES}}) {
	my $tmp = tmpdir($package);

	next if not -d $tmp;

	@elf_files = ();
	find({
			wanted => \&testfile,
			no_chdir => 1,
		 }, $tmp);
	next if not @elf_files;
	# Consistent order;
	@elf_files = sort(@elf_files);
	my ($unique_files, $hardlinks) = find_hardlinks(@elf_files);
	if ($create_multifile and @{$unique_files} > 1 and not is_udeb($package)) {
		my $objcopy = cross_command($package, 'objcopy');
		my $ma_dir = dpkg_architecture_value('DEB_HOST_MULTIARCH');
		my $dwz_dir = "usr/lib/debug/.dwz/${ma_dir}";
		my $m = "${dwz_dir}/${package}.debug";
		my @dwz_options = ("-m${tmp}/${m}", "-M/${m}");
		install_dir("${tmp}/${dwz_dir}");
		doit('dwz', @dwz_options, @{$dh{U_PARAMS}}, '--', @{$unique_files});
		if ( -f "${tmp}/${m}") {
			doit($objcopy, '--compress-debug-sections', "${tmp}/${m}");
		} else {
			error("dwz failed to create a multifile as requested") if $create_multifile ne 'auto';
			warning("No dwz multifile created, but not explicitly requested either so ignoring it.");
			warning("Common issues include no debug information at all (missing -g) and");
			warning("compressed debug information (#931891).");
			# Clean up after ourselves to avoid leaving empty directories in packages
			doit('rmdir', '-p', '--ignore-fail-on-non-empty', "${tmp}/usr/lib/debug/.dwz/${ma_dir}");
		}
	} else {
		xargs($unique_files, 'dwz', @{$dh{U_PARAMS}}, '--');
	}


	# Now change over any files we can that used to be hard links so
	# they are again.
	for my $hardlink (keys %{$hardlinks}) {
		my $target = $hardlinks->{$hardlink};
		# Remove old file.
		rm_files($hardlink);
		# Make new hardlink.
		doit('ln', '-f', $target, $hardlink);
	}
}

=head1 SEE ALSO

L<debhelper(7)>

This program is a part of debhelper.

=head1 AUTHOR

Niels Thykier <niels@thykier.net>

=cut