File Coverage

blib/lib/ELF/Writer.pm

Criterion	Covered	Total	%
statement	144	202	71.2
branch	43	132	32.5
condition	12	43	27.9
subroutine	28	32	87.5
pod	0	14	0.0
total	227	423	53.6

package ELF::Writer;
use Moo 2;
use Carp;
use IO::File;
use namespace::clean;

our $VERSION= '0.000_004';

# ABSTRACT: Encode elf files with pure-perl


sub _init_enum {
	my ($to_sym, $from_sym, @name_to_num)= @_;
	%$from_sym= @name_to_num;
	%$to_sym= reverse @name_to_num;
}


our (%class_to_sym, %class_from_sym);
_init_enum(\%class_to_sym, \%class_from_sym,
	'32bit' => 1,
	'64bit' => 2,
);

has class => ( is => 'rw', coerce => sub {
	my $x= $class_from_sym{$_[0]};
	defined $x? $x
		: (int($_[0]) == $_[0])? $_[0]
		: croak "$_[0] is not a valid 'class'"
});

sub class_sym {
	my $self= shift;
	$self->class($_[0]) if @_;
	my $v= $self->class;
	$class_to_sym{$v} || $v
}


our (%data_to_sym, %data_from_sym);
_init_enum(\%data_to_sym, \%data_from_sym,
	'2LSB' => 1,
	'2MSB' => 2,
);

has data => ( is => 'rw', coerce => sub {
	my $x= $data_from_sym{$_[0]};
	defined $x? $x
		: (int($_[0]) == $_[0])? $_[0]
		: croak "$_[0] is not a valid 'data'"
});

sub data_sym {
	my $self= shift;
	$self->data($_[0]) if @_;
	my $v= $self->data;
	$data_to_sym{$v} || $v
}


has header_version  => ( is => 'rw', default => sub { 1 } );


our (%osabi_to_sym, %osabi_from_sym);
_init_enum(\%osabi_to_sym, \%osabi_from_sym,
	'SystemV'  => 0,
	'HP-UX'    => 1,
	'NetBSD'   => 2,
	'Linux'    => 3,
	'Solaris'  => 6,
	'AIX'      => 7,
	'IRIX'     => 8,
	'FreeBSD'  => 9,
	'OpenBSD'  => 0x0C,
	'OpenVMS'  => 0x0D,
);

has osabi => ( is => 'rw', coerce => sub {
	my $x= $osabi_from_sym{$_[0]};
	defined $x? $x
		: (int($_[0]) == $_[0])? $_[0]
		: croak "$_[0] is not a valid 'osabi'"
});

sub osabi_sym {
	my $self= shift;
	$self->osabi($_[0]) if @_;
	my $v= $self->osabi;
	$osabi_to_sym{$v} || $v
}


has osabi_version   => ( is => 'rw', default => sub { 0 } );

our (%type_to_sym, %type_from_sym);
_init_enum(\%type_to_sym, \%type_from_sym,
	'none'        => 0,
	'relocatable' => 1,
	'executable'  => 2,
	'shared'      => 3,
	'core'        => 4,
);

has type => ( is => 'rw', coerce => sub {
	my $x= $type_from_sym{$_[0]};
	defined $x? $x
		: (int($_[0]) == $_[0])? $_[0]
		: croak "$_[0] is not a valid 'type'"
});

sub type_sym {
	my $self= shift;
	$self->type($_[0]) if @_;
	my $v= $self->type;
	$type_to_sym{$v} || $v
}


our (%machine_to_sym, %machine_from_sym);
_init_enum(\%machine_to_sym, \%machine_from_sym,
	'SPARC'       => 0x02,
	'i386'        => 0x03,
	'Motorola68K' => 0x04,
	'Motorola88K' => 0x05,
	'i860'        => 0x07,
	'MIPS-RS3000' => 0x08,
	'MIPS-RS4000' => 0xA0,
	'PowerPC'     => 0x14,
	'ARM'         => 0x28,
	'SuperH'      => 0x2A,
	'IA-64'       => 0x32,
	'x86-64'      => 0x3E,
	'AArch64'     => 0xB7,
);

has machine => ( is => 'rw', coerce => sub {
	my $x= $machine_from_sym{$_[0]};
	defined $x? $x
		: (int($_[0]) == $_[0])? $_[0]
		: croak "$_[0] is not a valid 'machine'"
});

sub machine_sym {
	my $self= shift;
	$self->machine($_[0]) if @_;
	my $v= $self->machine;
	$machine_to_sym{$v} || $v
}


has version         => ( is => 'rw', default => sub { 1 } );

has flags           => ( is => 'rw', default => sub { 0 } );

has entry_point     => ( is => 'rw' );


our $Magic= "\x7fELF";

sub elf_header_len {
	my $class= shift->class;
	return $class == 1? 52
		: $class == 2? 64
		: croak "Don't know structs for elf class $class";
}
our @Elf_Header_Pack= (
	'a4 C C C C C a7 S< S< L< L< L< L< L< S< S< S< S< S< S<', # 32-bit LE
	'a4 C C C C C a7 S> S> L> L> L> L> L> S> S> S> S> S> S>', # 32-bit BE
	'a4 C C C C C a7 S< S< L< Q< Q< Q< L< S< S< S< S< S< S<', # 64-bit LE
	'a4 C C C C C a7 S> S> L> Q> Q> Q> L> S> S> S> S> S> S>', # 64-bit BE
);
sub _elf_header_packstr {
	my ($self, $encoding)= @_;
	$encoding= $self->_encoding unless defined $encoding;
	$Elf_Header_Pack[ $encoding ];
}

sub segment_header_elem_len {
	my $class= shift->class;
	return $class == 1? 32
		: $class == 2? 56
		: croak "Don't know structs for elf class $class";
}
# Note! there is also a field swap between 32bit and 64bit
our @Segment_Header_Pack= (
	'L< L< L< L< L< L< L< L<',
	'L> L> L> L> L> L> L> L>',
	'L< L< Q< Q< Q< Q< Q< Q<',
	'L> L> Q> Q> Q> Q> Q> Q>',
);
sub _segment_header_packstr {
	my ($self, $encoding)= @_;
	$encoding= $self->_encoding unless defined $encoding;
	$Segment_Header_Pack[ $encoding ];
}

sub section_header_elem_len {
	my $class= shift->class;
	return $class == 1? 40
		: $class == 2? 64
		: croak "Don't know structs for elf class $class";
}
our @Section_Header_Pack= (
	'L< L< L< L< L< L< L< L< L< L<',
	'L> L> L> L> L> L> L> L> L> L>',
	'L< L< Q< Q< Q< Q< L< L< Q< Q<',
	'L> L> Q> Q> Q> Q> L> L> Q> Q>',
);
sub _section_header_packstr {
	my ($self, $encoding)= @_;
	$encoding= $self->_encoding unless defined $encoding;
	$Section_Header_Pack[ $encoding ];
}

# Returns a number 0..3 used by the various routines when packing binary data
sub _encoding {
	my $self= shift;
	my $endian= $self->data;
	my $bits=   $self->class;
	defined $endian && $endian > 0 && $endian < 3 or croak "Can't encode for data=$endian";
	defined $bits && $bits > 0 && $bits < 3 or croak "Can't encode for class=$bits";
	return ($bits-1)*2 + ($endian-1);
}


has segments => ( is => 'rw', coerce => \&_coerce_segments, default => sub { [] } );
sub segment_count { scalar @{ shift->segments } }
sub segment_list { @{ shift->segments } }


has sections => ( is => 'rw', coerce => \&_coerce_sections, default => sub { [] } );
sub section_count { scalar @{ shift->sections } }
sub section_list { @{ shift->sections } }

has section_name_string_table_idx => ( is => 'rw' );


sub serialize {
	my $self= shift;

	# Faster than checking bit lengths on every field ourself
	use warnings FATAL => 'pack';

	# Make sure all required attributes are defined
	defined($self->$_) || croak "Attribute $_ is not defined"
		for qw( class data osabi type machine header_version osabi_version version entry_point );

	# Clone the segments and sections so that our changes don't affect the
	# configuration the user built.
	my @segments= map { $_->clone } $self->segment_list;
	my @sections= map { $_->clone } $self->section_list;
	my $segment_table;
	my $section_table;

	# Now apply defaults and set numbering for diagostics of errors
	my $i= 0;
	for (@segments) {
		$_->_index($i++);
		$self->_apply_segment_defaults($_);

		# There can be one segment which loads the segment table itself
		# into the program's address space.  If used, we track the pointer
		# to that segment.  We also clear it's 'data' and set it's 'size'
		# to keep from confusing the code below.
		if ($_->type == 6) {
			croak "There can be only one segment of type 'phdr'"
				if defined $segment_table;
			$segment_table= $_;
			$segment_table->data(undef);
			$segment_table->size($self->segment_header_len * @segments);
		}
	}
	$i= 0;
	for (@sections) {
		$_->_index($i++);
		$self->_apply_section_defaults($_);
	}

	# Build a list of every defined range of data in the file,
	# and a list of every segment/section which needs automatically placed.
	my @defined_ranges;
	my @auto_offset;
	for (@segments, @sections) {
		# size is guaranteed to be defined by "_apply...defaults()"
		# Data might not be defined if the user just wanted to point the
		# segment at something, and offset might not be defined if the user
		# just wants it appended wherever.
		if (!defined $_->offset) {
			push @auto_offset, $_;
		}
		else {
			$_->offset >= 0 or croak $_->_name." offset cannot be negative";
			push @defined_ranges, $_
				if defined $_->data && length $_->data;
		}
	}

	if (@sections) {
		# First section must always be the NULL section.  If the user forgot this
		# then their indicies might be off.
		$sections[0]->type == 0
			or croak "Section 0 must be type NULL";
		# Sections may not overlap, regardless of whether the user attached data to them
		my $prev_end= 0;
		my $prev;
		for (sort { $a->offset <=> $b->offset } $self->section_list) {
			croak 'Section overlap between '.$_->_name.' and '.$prev->_name
				if $_->offset < $prev_end;
			$prev_end= $_->offset + $_->size;
		}
	}

	# Each segment and section can define data to be written to the file,
	# but segments can overlap sections.  Make sure their defined data doesn't
	# conflict, or we wouldn't know which to write.
	my $prev;
	my $prev_end= $self->elf_header_len;
	my $first_data;
	@defined_ranges= sort { $a->data_offset <=> $b->data_offset } @defined_ranges;
	for (@defined_ranges) {
		croak 'Data overlap between '.$_->_name.' and '.($prev? $prev->_name : 'ELF header')
			if $_->data_offset < $prev_end;
		$prev= $_;
		$prev_end= $_->data_offset + $_->size;
	}

	# For each segment or section that needs an offset assigned, append to
	# end of file.
	for (@auto_offset) {
		my $align= $_->_required_file_alignment;
		$prev_end= int(($prev_end + $align - 1) / $align) * $align;
		$_->offset($prev_end);
		push @defined_ranges, $_ if defined $_->data && length $_->data;
		$prev_end += $_->size;
	}

	# Now, every segment and section have an offset and a length.
	# We can now encode the tables.
	my @insert;
	if (@segments) {
		my $segment_table_data= '';
		$segment_table_data .= $self->_serialize_segment_header($_)
			for @segments;
		# The user might have defined this segment on their own.
		# Otherwise we just create a dummy to use below.
		if (!defined $segment_table) {
			$segment_table= ELF::Writer::Segment->new(
				align => 8,
				filesize => length($segment_table_data),
				data => $segment_table_data,
			);
			push @insert, $segment_table;
		} else {
			$segment_table->data($segment_table_data);
		}
	}
	if (@sections) {
		my $section_table_data= '';
		$section_table_data .= $self->_serialize_section_header($_)
			for @sections;

		$section_table= ELF::Writer::Segment->new(
			align => 8,
			filesize => length($section_table_data),
			data => $section_table_data,
		);
		push @insert, $section_table;
	}

	# Find a spot for the segment and/or section tables.
	# Due to alignment, there is probably room to squeeze the table(s) inbetween
	# other defined ranges.  Else, put them at the end.
	$prev_end= $self->elf_header_len;
	for (my $i= 0; @insert and $i <= @defined_ranges; ++$i) {
		my $align= $insert[0]->_required_file_alignment;
		$prev_end= int(($prev_end + $align-1) / $align) * $align;
		if ($i == @defined_ranges
			or $prev_end + $insert[0]->size <= $defined_ranges[$i]->data_offset
		) {
			$insert[0]->offset($prev_end);
			splice @defined_ranges, $i, 0, shift @insert;
		}
	}

	# Now, we can finally encode the ELF header.
	my $header= pack($self->_elf_header_packstr,
		$Magic, $self->class, $self->data, $self->header_version,
		$self->osabi, $self->osabi_version, '',
		$self->type, $self->machine, $self->version, $self->entry_point,
		($segment_table? $segment_table->offset : 0),
		($section_table? $section_table->offset : 0),
		$self->flags, $self->elf_header_len,
		$self->segment_header_elem_len, $self->segment_count,
		$self->section_header_elem_len, $self->section_count,
		$self->section_name_string_table_idx || 0,
	);
	# sanity check
	length($header) == $self->elf_header_len
		or croak "Elf header len mismatch";

	# Write out the header and each range of defined bytes, padded with NULs as needed.
	my $data= $header;
	for (@defined_ranges) {
		my $pad= $_->data_offset - length($data);
		$data .= "\0" x $pad if $pad;
		$data .= $_->data;
	}
	return $data;
}

sub _serialize_segment_header {
	my ($self, $seg)= @_;

	# Faster than checking bit lengths on every field ourself
	use warnings FATAL => 'pack';

	# Make sure all required attributes are defined
	defined $seg->$_ or croak "Attribute $_ is not defined"
		for qw( type offset virt_addr align );

	my $filesize= $seg->filesize;
	$filesize= length($seg->data) + $seg->data_offset
		unless defined $filesize;

	my $align= $seg->align;
	my $memsize= $seg->memsize;
	$memsize= int(($filesize + $align - 1) / $align) * $align
		unless defined $memsize;

	# 'flags' moves depending on 32 vs 64 bit, so changing the pack string isn't enough
	return $self->_encoding < 2?
		pack($self->_segment_header_packstr,
			$seg->type, $seg->offset, $seg->virt_addr, $seg->phys_addr || 0,
			$filesize, $memsize, $seg->flags, $seg->align
		)
		: pack($self->_segment_header_packstr,
			$seg->type, $seg->flags, $seg->offset, $seg->virt_addr,
			$seg->phys_addr || 0, $filesize, $memsize, $seg->align
		);
}

sub _serialize_section_header {
	my ($self, $sec)= @_;

	# Make sure all required attributes are defined
	defined $sec->$_ or croak "Attribute $_ is not defined"
		for qw( type name flags addr offset size link info addralign entsize );

	# Faster than checking bit lengths on every field ourself
	use warnings FATAL => 'pack';

	return pack($self->_section_header_packstr,
		$sec->name, $sec->type, $sec->flags, $sec->addr, $sec->offset,
		$sec->size, $sec->link, $sec->info, $sec->align, $sec->entry_size
	);
}


sub write_file {
	my ($self, $filename, $mode)= @_;
	$mode= 0755 unless defined $mode;
	require File::Temp;
	my ($fh, $tmpname)= File::Temp::tempfile( $filename.'-XXXXXX' );
	print $fh $self->serialize or croak "write: $!";
	close $fh or croak "close: $!";
	chmod($mode, $tmpname) or croak "chmod: $!";
	rename($tmpname, $filename) or croak "rename: $!";
}

# coerce arrayref of hashrefs into arrayref of objects
sub _coerce_segments {
	my $spec= shift;
	return [ map { (__PACKAGE__.'::Segment')->coerce($_) } @$spec ];
}

# coerce arrayref of hashrefs into arrayref of objects
sub _coerce_sections {
	my $spec= shift;
	return [ map { (__PACKAGE__.'::Section')->coerce($_) } @$spec ];
}

# Overridden by subclasses for machine-specific defaults
sub _apply_section_defaults {
	my ($self, $sec)= @_;
	# Undef type is "null" type 0
	my $type= $sec->type;
	defined $type
		or $sec->type($type= 0);
	my $offset= $sec->offset;
	my $size= $sec->size;

	if ($type == 0) { # 'null'
		# Ensure length and offset are zero
		$size= $sec->size(0) unless defined $size;
		$offset= $sec->offset(0) unless defined $offset;
		croak "null section should have offset=0 and size=0"
			if $offset || $size;
	}
	elsif ($type == 8) { # 'nobits'
		# Offset can be set but ensure size is zero
		$size= $sec->size(0) unless defined $size;
		croak "nobits section should have size=0"
			if $size;

	}
	else {
		# 'size' is required, but can be computed from 'data' and 'data_offset'.
		if (!defined $size) {
			defined $sec->data or croak "Section must define 'size' or 'data'";
			$sec->size($sec->data_start + length($sec->data));
		}
	}
}

# Overridden by subclasses for machine-specific defaults
sub _apply_segment_defaults {
	my ($self, $seg)= @_;
	# Undef type is "null" type 0
	my $type= $seg->type;
	defined $type
		or $seg->type($type= 0);
	my $offset= $seg->offset;
	my $filesize= $seg->filesize;

	if ($type == 0) { # 'null'
		# Ensure length and offset are zero
		$filesize= $seg->filesize(0) unless defined $filesize;
		$offset= $seg->offset(0) unless defined $offset;
		croak "null segment should have offset=0 and filesize=0"
			if $offset || $filesize;
	}
	else {
		# 'filesize' is required, but can be computed from 'data' and 'data_offset'
		if (!defined $filesize) {
			defined $seg->data or croak "Segment must define 'filesize' or 'data'";
			$filesize= $seg->filesize($seg->data_start + length($seg->data));
		}
		# Default memsize to filesize
		$seg->memsize($filesize) unless defined $seg->memsize;
	}
}

# Load last so make sure data is initialized
require ELF::Writer::Segment;
require ELF::Writer::Section;

1;

__END__