#!/usr/bin/perl -w

use Getopt::Std;

use constant MINROMSIZE => 8192;
use constant MAXROMSIZE => 262144;

use constant PCI_PTR_LOC => 0x18;	# from beginning of ROM
use constant PCI_HDR_SIZE => 0x18;
use constant PNP_PTR_LOC => 0x1a;	# from beginning of ROM
use constant PNP_HDR_SIZE => 0x20;
use constant PNP_CHKSUM_OFF => 0x9;	# bytes from beginning of PnP header
use constant PNP_DEVICE_OFF => 0x10;	# bytes from beginning of PnP header
use constant PCI_VEND_ID_OFF => 0x4;	# bytes from beginning of PCI header
use constant PCI_DEV_ID_OFF => 0x6;	# bytes from beginning of PCI header
use constant PCI_SIZE_OFF => 0x10;	# bytes from beginning of PCI header

use constant UNDI_PTR_LOC => 0x16;	# from beginning of ROM
use constant UNDI_HDR_SIZE => 0x16;
use constant UNDI_CHKSUM_OFF => 0x05;

use strict;

use vars qw(%opts);

use bytes;

sub getromsize ($) {
	my ($romref) = @_;
	my $i;

	print STDERR "BIOS extension ROM Image did not start with 0x55 0xAA\n"
		if (substr($$romref, 0, 2) ne "\x55\xaa");
	my $size = ord(substr($$romref, 2, 1)) * 512;
	for ($i = MINROMSIZE; $i < MAXROMSIZE and $i < $size; $i *= 2) { }
	print STDERR "$size is a strange size for a boot ROM\n"
		if ($size > 0 and $i > $size);
	return ($size);
}

sub addident ($) {
	my ($romref) = @_;

	return (0) unless (my $s = $opts{'i'});
	# include the terminating NUL byte too
	$s .= "\x00";
	my $len = length($s);
	# Put the identifier in only if the space is blank
	my $pos = length($$romref) - $len - 2;
	return (0) if (substr($$romref, $pos, $len) ne ("\xFF" x $len));
	substr($$romref, $pos, $len) = $s;
	return ($pos);
}

sub pcipnpheaders ($$) {
	my ($romref, $identoffset) = @_;
	my ($pci_hdr_offset, $pnp_hdr_offset);

	$pci_hdr_offset = unpack('v', substr($$romref, PCI_PTR_LOC, 2));
	$pnp_hdr_offset = unpack('v', substr($$romref, PNP_PTR_LOC, 2));
	# Sanity checks
	if ($pci_hdr_offset < PCI_PTR_LOC + 2
		or $pci_hdr_offset > length($$romref) - PCI_HDR_SIZE
		or $pnp_hdr_offset < PNP_PTR_LOC + 2
		or $pnp_hdr_offset > length($$romref) - PNP_HDR_SIZE
		or substr($$romref, $pci_hdr_offset, 4) ne 'PCIR'
		or substr($$romref, $pnp_hdr_offset, 4) ne '$PnP') {
		$pci_hdr_offset = $pnp_hdr_offset = 0;
	} else {
		printf "PCI header at %#x and PnP header at %#x\n",
			$pci_hdr_offset, $pnp_hdr_offset if $opts{'v'};
	}
	if ($pci_hdr_offset > 0) {
		my ($pci_vendor_id, $pci_device_id);
		# if no -p option, just report what's there
		if (!defined($opts{'p'})) {
			$pci_vendor_id = unpack('v', substr($$romref, $pci_hdr_offset+PCI_VEND_ID_OFF, 2));
			$pci_device_id = unpack('v', substr($$romref, $pci_hdr_offset+PCI_DEV_ID_OFF, 2));
			printf "PCI Vendor ID %#x Device ID %#x\n",
				$pci_vendor_id, $pci_device_id;
		} else {
			substr($$romref, $pci_hdr_offset + PCI_SIZE_OFF, 2)
				= pack('v', length($$romref) / 512);
			($pci_vendor_id, $pci_device_id) = split(/,/, $opts{'p'});
			substr($$romref, $pci_hdr_offset+PCI_VEND_ID_OFF, 2)
				= pack('v', oct($pci_vendor_id)) if ($pci_vendor_id);
			substr($$romref, $pci_hdr_offset+PCI_DEV_ID_OFF, 2)
				= pack('v', oct($pci_device_id)) if ($pci_device_id);
		}
	}
	if ($pnp_hdr_offset > 0) {
		if (defined($identoffset)) {
			# Point to device id string at end of ROM image
			substr($$romref, $pnp_hdr_offset+PNP_DEVICE_OFF, 2)
				= pack('v', $identoffset);
		}
		substr($$romref, $pnp_hdr_offset+PNP_CHKSUM_OFF, 1) = "\x00";
		my $sum = unpack('%8C*', substr($$romref, $pnp_hdr_offset,
			PNP_HDR_SIZE));
		substr($$romref, $pnp_hdr_offset+PNP_CHKSUM_OFF, 1) = chr(256 - $sum);
	}
}

sub undiheaders ($) {
	my ($romref) = @_;
	my ($undi_hdr_offset);

	$undi_hdr_offset = unpack('v', substr($$romref, UNDI_PTR_LOC, 2));
	# Sanity checks
	if ($undi_hdr_offset < UNDI_PTR_LOC + 2
		or $undi_hdr_offset > length($$romref) - UNDI_HDR_SIZE
		or substr($$romref, $undi_hdr_offset, 4) ne 'UNDI') {
		$undi_hdr_offset = 0;
	} else {
		printf "UNDI header at %#x\n", $undi_hdr_offset if $opts{'v'};
	}
	if ($undi_hdr_offset > 0) {
		substr($$romref, $undi_hdr_offset+UNDI_CHKSUM_OFF, 1) = "\x00";
		my $sum = unpack('%8C*', substr($$romref, $undi_hdr_offset,
			UNDI_HDR_SIZE));
		substr($$romref, $undi_hdr_offset+UNDI_CHKSUM_OFF, 1) = chr(256 - $sum);
	}
}

sub writerom ($$) {
	my ($filename, $romref) = @_;

	open(R, ">$filename") or die "$filename: $!\n";
	print R $$romref;
	close(R);
}

sub checksum ($$) {
	my ($romref, $romsize) = @_;

	substr($$romref, 6, 1) = "\x00";
	my $sum = unpack('%8C*', substr($$romref, 0, $romsize));
	substr($$romref, 6, 1) = chr(256 - $sum);
	# Double check
	$sum = unpack('%8C*', substr($$romref, 0, $romsize));
	if ($sum != 0) {
		print "Checksum fails\n"
	} elsif ($opts{'v'}) {
		print "Checksum ok\n";
	}
}

sub makerom () {
	my ($rom, $romsize, $stubsize);

	getopts('3xni:p:s:v', \%opts);
	$ARGV[0] or die "Usage: $0 [-s romsize] [-i ident] [-p vendorid,deviceid] [-n] [-x] [-3] rom-file\n";
	open(R, $ARGV[0]) or die "$ARGV[0]: $!\n";
	# Read in the whole ROM in one gulp
	my $filesize = read(R, $rom, MAXROMSIZE+1);
	close(R);
	defined($filesize) and $filesize >= 3 or die "Cannot get first 3 bytes of file\n";
	print "$filesize bytes read\n" if $opts{'v'};
	# If PXE image, just fill the length field and write it out
	if ($opts{'x'}) {
		substr($rom, 2, 1) = chr((length($rom) + 511) / 512);
		writerom($ARGV[0], \$rom);
		return;
	}
	# Size specified with -s overrides value in 3rd byte in image
	# -s 0 means round up to next 512 byte block
	if (defined($opts{'s'})) {
		if (($romsize = oct($opts{'s'})) <= 0) {
			# NB: This roundup trick only works on powers of 2
			$romsize = ($filesize + 511) & ~511
		}
	} else {
		# Shrink romsize down to the smallest power of two that will do
		for ($romsize = MAXROMSIZE;
		     $romsize > MINROMSIZE and $romsize >= 2*$filesize;
		     $romsize /= 2) { }
	}
	if ($filesize > $romsize) {
		print STDERR "ROM size of $romsize not big enough for data, ";
		# NB: This roundup trick only works on powers of 2
		$romsize = ($filesize + 511) & ~511;
		print "will use $romsize instead\n"
	}
	# Pad with 0xFF to $romsize
	$rom .= "\xFF" x ($romsize - length($rom));
	# If this is a stub ROM, don't force header size to the full amount
	if (!$opts{'n'}) {
		if ($romsize >= 128 * 1024) {
			print "Warning: ROM size exceeds extension BIOS limit\n";
		}
		substr($rom, 2, 1) = chr(($romsize / 512) % 256);
	} else {
		$stubsize = ord(substr($rom, 2, 1)) * 512;
		print "Stub size is $stubsize\n" if $opts{'v'};
	}
	print "ROM size is $romsize\n" if $opts{'v'};
	# set the product string only if we don't have one yet
	my $pnp_hdr_offset = unpack('v', substr($rom, PNP_PTR_LOC, 2));
	my $identoffset = substr($rom, $pnp_hdr_offset+PNP_DEVICE_OFF, 2) eq "\0\0" ? addident(\$rom) : undef;
	pcipnpheaders(\$rom, $identoffset);
	undiheaders(\$rom);
	# 3c503 requires last two bytes to be 0x80
	substr($rom, MINROMSIZE-2, 2) = "\x80\x80"
		if ($opts{'3'} and $romsize == MINROMSIZE);
	checksum(\$rom, $opts{'n'} ? $stubsize : $romsize);
	writerom($ARGV[0], \$rom);
}

sub modrom () {
	my ($rom);

	getopts('p:v', \%opts);
	$ARGV[0] or die "Usage: $0 [-p vendorid,deviceid] rom-file\n";
	open(R, $ARGV[0]) or die "$ARGV[0]: $!\n";
	# Read in the whole ROM in one gulp
	my $filesize = read(R, $rom, MAXROMSIZE+1);
	close(R);
	defined($filesize) and $filesize >= 3 or die "Cannot get first 3 bytes of file\n";
	print "$filesize bytes read\n" if $opts{'v'};
	pcipnpheaders(\$rom, undef);
	undiheaders(\$rom);
	checksum(\$rom, ord(substr($rom, 2, 1)) * 512);
	writerom($ARGV[0], \$rom);
}

# Main routine. See how we were called and behave accordingly
if ($0 =~ m:modrom(\.pl)?$:) {
	modrom();
} else {
	makerom();
}
exit(0);