2014-05-31

Restoring EFI NVRAM boot entries with rEFInd and Rufus

So, you reinstalled Windows, and it somehow screwed the nice EFI entry you had that booted your meticulously crafted EFI system partition? You know, the one you use with rEFInd or ELILO or whatever, to multiboot Linux, Windows, etc., and that has other goodies such as the EFI shell...

Well, here's how you can sort yourself out (shamelessly adapted from the always awesome and extremely comprehensive Arch Linux documentation):
  • Download the latest rEFInd CD-R image from here.
  • Extract the ISO and use Rufus to create a bootable USB drive. Make sure that, when you create the USB, you have "GPT partition scheme for UEFI computer" selected, under "Partition scheme and target system type".
  • Boot your computer in UEFI mode, and enter the EFI BIOS to select the USB as your boot device
  • On the rEFInd screen select "Start EFI shell".
  • At the 2.0 Shell > prompt type:
    bcfg boot dump

    This should confirm that some of your old entries have been unceremoniously wiped out by Windows.
  • Find the disk on which your old EFI partition resides by issuing something like:
    dir fs0:\efi

    NB: you can use the map command to get a list of all the disks and partitions detected during boot.
  • Once you have the proper fs# information (and provided you want to add an entry that boots into a rEFInd installed on your EFI system partition under EFI\refind\refind_x64.efi), issue something like:
    bcfg boot add 0 fs0:\EFI\refind\refind_x64.efi rEFInd
    Note: If needed you can also use bcfg boot rm # to remove existing entries.
  • Confirm that your entry has been properly installed as the first option, by re-issuing bcfg boot dump. Then remove the USB, reset your machine, and you should find that everything is back to normal.
NOTE: Make sure you use the latest rEFInd if you want an EFI shell that includes bcfg. Not all EFI shells will contain that command!

2014-05-30

RTF - Where's the FM?

I mean a hands-on manual on how to create an Rich Text Format file from scratch, not the friggin' 200 pages  specs! Plus, only Microsoft would provide a 200 pages Word Document as an executable... Oh well, it's not like I never saw IBM (or was it Intel?) providing some source code as a PDF file with page numbering.

Man, what a struggle to figure out how to get Arabic RTF content to properly display in an app's Rich Edit control.

If you try to be smart and have Wordpad produce your RTF for you, and even if you set your Arabic text to use an Unicode font, you end up with something like:

{\rtf1 ... {\fonttbl{\f0\fnil\fcharset0 Courier New;}{\f1\fnil\fcharset178 @Arial Unicode MS;}}
\pard\ltrpar\f0 Some blurb\f1\rtlch\lang1025\'da\'e3\'d1 \'c7\'e1\'d5\'e3\'cf\b0\f0\ltrch\lang6153\par
}
...which results in UTTER GARBAGE on screen in place of the Arabic!

I can't help but ask: what is the point of using an Unicode font, really, if that insanely dumb word processor that is Wordpad still insists on living in the 1980s, and switches codepages to insert ASCII codepoints instead?

So here's what you actually want to do, manually:
  • remove the \lang switch
  • insert pure Unicode codepoints using \u
But of course, it wouldn't be as backwards as possible if Microsoft didn't also force you to specify Unicode codepoints in decimal, with no means whatsoever of specifying hex instead. So even if you know the Arabic UTF-16 sequence you want to insert, you will have to spend some time doing your decimal conversions, to, at last, get the properly working:

{\rtf1 ... {\fonttbl{\f0\fnil\fcharset0 Courier New;}{\f1\fnil\fcharset178 @Arial Unicode MS;}}
\pard\ltrpar\f0 Some blurb\f1\rtlch\u1575?\u1604?\u1589?\u1605?\u1583? \u1593?\u1605?\u1585?\ltrch\f0\
}

Heed my advice: If you design your format around the idea that no human will ever need to edit some data in a hurry in it, you're designing it all wrong...

As an aside, the above is also the reason why little-endian is an utter abomination that should be banned from the face of this earth: If I'm in a computer-controlled commercial airplane, that's lost all input, and, on account of the ground approaching fast, I'm in a bit of a hurry to figure out from a memory dump where the automatic pilot might store its altitude, to manually alter it, you bet that I'm gonna hope that whoever designed that plane picked a big-endian CPU, to slightly increase the probability of myself and all the other passengers not ending up as a pancake...

First rule of designing anything is to design with the idea that humans will always need to interact with your stuff, in ways that you'll never be able to devise.

So, Microsoft, next time you want to design something like RTF, please RTFM of Design rules and try to make it just a bit easier on people who need to manually interact with your stuff...

2014-05-29

Compiling and installing Grub2 for standalone USB boot

The goal here, is to produce the necessary set of files, to be written to an USB Flash Drive using dd (rather than using the Grub installer), so that it will boot through Grub 2.x and be able to process an existing grub.cfg that sits there.

As usual, we start from nothing. I'll also assume that you know nothing about the intricacies of Grub 2 with regards to the creation of a bootable USB, so let me start with a couple of primers:

  1. For a BIOS/USB boot, Grub 2 basically works on the principle of a standard MBR (boot.img), that calls a custom second stage (core.img), which usually sits right after the MBR (sector 1, or 0x200 on the UFD) and which is a flat compressed image containing the Grub 2 kernel plus a user hand-picked set of modules (.mod).
    These modules, which get added to the base kernel, should usually limit themselves to the ones required to access the set of file systems you want Grub to be able to read a config file from and load more individual modules (some of which need to be loaded to parse the config, such as normal.mod or terminal.mod).
    As you may expect, the modules you embed with the Grub kernel and the modules you load from the target filesystem are exactly the same, so you have some choice on whether to add them to the core image or load them from the filesystem.
     
  2. You most certainly do NOT want to use the automated Grub installer in order to boot an UFD. This is because the Grub installer is designed to try to boot the OS it is running from, rather than try to boot a random target in generic fashion. Thus, if you try to follow the myriad of quick Grub 2 guides you'll find floating around, you'll end up nowhere in terms of booting a FAT or NTFS USB Flash Drive, that should be isolated of everything else.
With the above in mind, it's time to get our hands dirty. Today, I'm going to use Linux, because my attempts to try to build the latest Grub 2 using either MinGW32 or cygwin failed miserably (crypto compilation issue for MinGW, Python issue for cygwin on top of the usual CRLF annoyances for shell scripts due to the lack of a .gitattributes). I sure wish I had the time to produce a set of fixes for Grub guys, but right now, that ain't gonna happen ⇒ Linux is is.

First step is to pick up the latest source, and, since we like living on the edge, we'll be using git rather than a release tarball:

git clone git://git.savannah.gnu.org/grub.git

Then, we bootstrap and attempt to configure for the smallest image size possible, by disabling NLS (which I had hoped would remove anything gettext but turns out not to be the case - see below).

cd grub
./autogen.sh
./configure --disable-nls
make -j2

After a few minutes, your compilation should succeed, and you should find that in the grub-core/ directory, you have a boot.img, kernel.img as well as a bunch of modules (.mod).

As explained above, boot.img is really our MBR, so that's good, but we're still missing the bunch of sectors we need to write right after that, that are meant to come from a core.img file.

The reason we don't have a core.img yet is because it is generated dynamically, and we need to tell Grub exactly what modules we want in there, as well as the disk location we want the kernel to look for additional modules and config files. To do just that, we need to use the Grub utility grub-mkimage.

Now that last part (telling grub that it should look at the USB generically and in isolation, and not give a damn about our current OS or disk setup) is what nobody on the Internet seems to have the foggiest clue about, so here goes: We'll want to tell Grub to use BIOS/MBR mode (not UEFI/GPT) and that we'll have one MBR partition on our UFD containing the boot data that's not included in boot.img/core.img and that it may need to proceed. And with BIOS setting our bootable UFD as the first disk (whatever gets booted is usually the first disk BIOS will list), we should tell Grub that our disk target is hd0. Furthermore, the first MBR partition on this drive will be identified as msdos1 (Grub calls MBR-like partitions msdos#, and GPT partitions gpt#, with the index starting at 1, rather than 0 as is the case for disks).

Thus, if we want to tell Grub that it needs to look for the first MBR partition on our bootable UFD device, we must specify (hd0,msdos1) as the root for our target.
With this being sorted, the only hard part remaining is figure out the basic modules we need, so that Grub has the ability to actually identify and read stuff on a partition that may be FAT, NTFS or exFAT. To cut a long story short, you'll need at least biosdisk and part_msdos, and then a module for each type of filesystem you want to be able to access. Hence the complete command:

cd grub-core/
../grub-mkimage -v -O i386-pc -d. -p\(hd0,msdos1\)/boot/grub biosdisk part_msdos fat ntfs exfat -o core.img

NB: If you want to know what the other options are for, just run ../grub-mkimage --help
Obviously, you could go crazy adding more file systems, but the one thing you want to pay attention is the size of core.img. That's because if you want to keep it safe and stay compatible with the largest choice of disk partitioning tools, you sure want to have core.img below 32KB - 512 bytes. The reason is there still exists a bunch of partitioning utilities out there that default to creating their first partition on the second "track" of the disk. And for most modern disks, including flash drives, a track will be exactly 64 sectors. What this all means is, if you don't want to harbour the possibility of overflowing core.img onto your partition data, you really don't want it to be larger than 32256 or 0x7E00 bytes.
OK, so now that we have core.img, it's probably a good idea to create a single partition on our UFD (May I suggest using Rufus to do just that? ;)) and format it to either FAT/FAT32, NTFS or exFAT.

Once this is done, we can flat-copy both the MBR, a.k.a. boot.img, and core.img onto those first sectors. The one thing you want to pay attention to here is, while copying core.img is no sweat, because we can just use a regular 512 byte sector size, for the MBR, you need to make sure that only the first 446 bytes of boot.img are copied, so as not to overwrite the partition data that also resides in the MBR and that has already been filled. So please pay close attention to the bs values below:

dd if=boot.img of=/dev/sdb bs=446 count=1
dd if=core.img of=/dev/sdb bs=512 seek=1 # seek=1 skips the first block (MBR)

Side note: Of course, instead of using plain old dd, one could have used Grub's custom grub-bios-setup like this:

../grub-bios-setup -d. -b ./boot.img -c ./core.img /dev/sdb

However, the whole point of this little post is to figure out a way to add Grub 2 support to Rufus, in which we'll have to do the copying of the img files without being able to rely on external tools. Thus I'd rather demonstrate that a dd copy works just as good as the Grub tool for this.
After having run the above, you may think that all that's left is copying a grub.cfg to /boot/grub/ onto your USB device, and watch the magic happen... but you'll be wrong.

Before you can even think about loading a grub.cfg, and at the very least, Grub MUST have loaded the following modules (which you'll find in your grub-core/ directory and that need to be copied on the target into a /boot/grub/i386-pc/ folder):
  • boot.mod
  • bufio.mod
  • crypto.mod
  • extcmd.mod
  • gettext.mod
  • normal.mod
  • terminal.mod
As to why the heck we still need gettext.mod, when we made sure we disabled NLS, and also why we must have crypto, when most usages of Grub don't care about it, your guess is as good as mine...

Finally, to confirm that everything works, you can add echo.mod to the list above, and create a /boot/grub/grub.cfg on your target with the following:

insmod echo
set timeout=5

menuentry "test" {
    echo "hello"
}

Try it, and you should find that your Grub 2 config is executing at long last, whether your target filesystem in FAT, NTFS or exFAT, and you can now build custom bootable Grub 2 USBs on top of that. Isn't that nice?

FINAL NOTE: In case you're using this to try boot an existing Grub 2 based ISO from USB (say Aros), be mindful that, since we are using the very latest Grub code, there is a chance that the modules from the ISO and the kernel we use in core may have some incompatibility. Especially, you may run into the obnoxious:

error: symbol 'grub_isprint' not found.

What this basically means is that there is a mismatch between your Grub 2 kernel version and Grub 2 module. To fix that you will need to use kernel and modules from the same source.