meta-measured updates

I’ve been grinding down updates to meta-measured slowly but surely over these past few days. This was started a while back but slowed to a stop when I got distracted by work on meta-selinux. Last week my work to upgrade the SELinux toolstack was merged upstream so I’m re-focusing on getting meta-measured back in shape. This is a quick run down on the changes.

General Maintenance and Release Tracking

I haven’t been chasing upstream much so most of this work has just been maintenance. The kernel in OE has moved forward with 4.1 the new stable in master. The read-only root file system class was broken when I tried a fresh master build the other day. When jumping in to start a refresh, finding core features broken can be a bit discouraging. Instead of taking on this fix immediately I figured it would be best to create a branch to track the latest release (fido) and get that working first. I’ve always avoided tracking OE releases because I don’t want to give the impression that meta-measured is in any way “stable”, as if having my master branch broken on a regular basis wasn’t a good enough indicator.

Seriously though, I kinda dropped the “chasing master” ball. Having a branch that follows the latest release is a good way to make getting everything up to date and it’s a good insurance policy against future breakage in master. So win / win on that. Fido still has a functional readonly-rootfs class so, for the 2 other people out there who have kicked the tires on meta-measured, fall back to a release branch. My goal is to keep at least one release branch in working order.

There are two changes between fido and the current master that have an impact on meta-measured. The first is the upgrade to GCC5. For the trousers and tpm-tools packages this requires a patch that I’ve gratefully borrowed from the hardworking people over at the Debian project. The other is meta-intel nuking the meta-nuc layer. This is a pretty minor change and I’m now using the measured-intel-corei7-64 that extends the intel-corei7-64 machine from meta-intel on the master branch. Fido still has the NUC machine so I’ll stick to that for Fido.


The first external submission to meta-measured came in a few months back. This was to add systemd support to the trousers package. I had done something similar to this as part of some work to get meta-measured working with the Edison but it was in the BSP layer. It really shouldn’t have been in the BSP layer to begin and my implementation was a hack regardless. The patch I received that adds this feature directly to meta-measured was well done so I’ve added it directly and removed my hack from the BSP.

The only bit I didn’t like from the patch was a utility script that loaded every TPM module under /lib/modules/$(uname -r). This seems a bit heavy handed given that modern Linux kernels autoload these modules when the device is detected. Pretty minor change though and this is now in meta-measured proper.

IMA and TPM2

I started playing around with configuring IMA a while back as a way to exercise the TPM2 that’s baked into the Minnowboard Max as part of PTT. I don’t have any specific plans to do much with IMA just yet but with the xattrs patches I pushed into meta-selinux I’m hoping to be able to support IMA appraisal. It would be a great use case and demonstration to show the utility of my xattr work with an OE image booting with IMA appraisal enforced from firstboot.

UEFI Breakage

I’ve been saving the bad news for last unfortunately. Somewhere in the changes that have been going on with OE, my bringing meta-measured up to date and flashing the firmware on my IVB NUC, measured-image-bootimg broke. I’m pretty sure this is a problem with the latest firmware for the NUC but that’s a guess. Grub2 comes up OK but tboot doesn’t seem to take over.

In prevous debugging I learned that tboot won’t log to VGA since UEFI doesn’t setup a text console for use by whatever executes after ExitBootServices() is called. It’s frame buffer only in UEFI world I guess. But tboot would still log to a serial device through direct I/O. Not this time though. Once Grub2 kicks off tboot my NUC is unresponsive and I get no additional output. Booting straight to the kernel from grub works fine but going the tboot route through multiboot2 isn’t working.

I’m pretty much out of debugging ideas here. My test system is getting a bit old and it’s the only UEFI system I have for use here so I’m writing this off as a loss for the time being. If anyone out there is testing this on a UEFI system I’d love to hear about whatever results you have to report.

Next steps

I’ve added the contributed systemd support to trousers but I haven’t enabled or tested systemd support for my reference images. This is next on my list of things to do. I’ve got trousers working on a systemd driven image previously in some work to wire a TPM up to an Edison system (more on this in the future hopefully) but I was working on on the reference Edison images. Stay tuned and hopefully I’ll have proper systemd support in the near future.

xattrs in OE rootfs part 2

This is an update on some work from a previous post. My xattr patches sat on the yocto mailing list waiting for meta-selinux maintainers to review them for about a month. I got a bit testy and even commented to another contributor off list about the possible need to fork given the lack of response from maintainers. Turns out that this contributor was using his gmail account but actually works for the same company as the maintainer. So about 24 hours later the maintainers magically reappeared and merged my patches!

I really have no interest in forking and maintaining meta-selinux so this was a win. Hopefully I didn’t look like too much of a jerk in the process … ¯_(ツ)_/¯ After a quick stint in a feature branch my xattr code was merged into meta-selinux master. This is only a step in the process though. These patches really belong in the openembedded-core repository. They can likely be moved with minimal effort on the technical side. Getting traction for these sorts of fringe features upstream however takes a bunch of time though, as demonstrated by the 2 months it took to get this into meta-selinux.

As a strategy I should probably prove out an additional use case beyond SELinux file labels. I did some work on meta-measured a while back to add basic IMA support. I really want to expand this to support IMA appraisal. I’m not a huge fan of local enforcement policies but this use case is a great example of build-time xattr usage that would demonstrate the utility of my xattr patches. This is all food for thought though at this point.

tboot 1.8.0 and UEFI

Version 1.8.0 of tboot was released a while back. This is a pretty big deal as the EFI support has been a long time coming. Anyone wanting to use tboot on a modern piece of hardware using EFI has been out of luck till now.

For the past week or so I’ve been slowly figuring out how to build an OE image with grub-efi, building the new version of tboot and then debugging an upgrade in meta-measured. My idea of a good time for sure.

As always the debugging was the hardest part, building the software was easy. For the most part tboot EFI “just worked” … after I figured out all the problems with kernel version and grub configuration. Hard parts were

  • realizing the Linux kernel image had to be the latest 3.14 version
  • debugging new kernel version
  • configuring grub
  • which modules needed to be built into grub

If you want the details you can see the full history on the meta-meausred github. The highlights are pretty simple:

multiboot2 in oe-core grub-efi

The grub-efi recipe in oe-core is a bit rigid. I’ve pushed a patch upstream that allows another layer (like meta-measured) to modify which grub modules are built into the grub EFI executable. It’s a tiny change but it makes all of the difference:

This lets us add modules to the grub EFI executable. I also had to cobble together a working grub multiboot2 configuration.

linux-yocto v3.14

Pairing this with the older 3.10 Yocto Linux kernel image will allow you to get through grub and tboot but the kernel will panic very early in the boot process. The newer 3.14 doesn’t suffer from this limitation.

The measured reference image in meta-measured used aufs to keep from having to mount the rootfs read/write. This is to keep the rootfs hash from changing across boots. I wrote the whole thing up a while back: Anyways aufs doesn’t work in 3.14 so I took the extra few minutes to migrate the image to use the read-only-rootfs IMAGE_FEATURE. This is a good thing regardless, aufs was being used as a shortcut. I hadn’t had the drive to fix this till it broke. Problem solved.

rough edges

I still haven’t figured out all of the details in grub and it’s configuration. The current configuration in meta-measured is sufficient to boot but something gets screwed up in setting up VGA output for tboot and the early kernel output. Currently grub displays an error message indicating that tboot won’t get a console and no VGA output will be shown till the kernel loads the DRM driver. Output is still available on the serial console so if you’ve got a reasonable test setup you can get all the data you need for debugging.

No lies, I’m a bit afraid of grub, guess I’ll have to get over it. The measured-image-bootimg has a menuentry for tboot and a normal linux boot. Booting the kernel using the linux and initrd grub commands provide normal VGA output but the multiboot2 config required by tboot does not. I take this to mean that grub is capable of doing all of the necessary VGA stuff but that it can’t pass this data through to tboot via multiboot2. More to come on this soon hopefully.

Till then, if you build this stuff and have feedback leave it here.

OE image package part 2

I spent the weekend in bed with a cold … and with a laptop hacking on ways to get OE rootfs images packaged and installed in other OE rootfs images. My solution isn’t great but it’s functional and it doesn’t require that every image be built in series. But before I get too far let’s go over what I set out to achieve and get a rough set of requirements:

  • I’m building a rootfs that itself contains other rootfs’. The inner rootfs’ will be VMs. The outer rootfs will be the host with the hypervisor (Xen dom0).
  • Build speeds are important so I’d like to share as much of the build infrastructure between VMs as possible.
  • Running builds in parallel is a good thing. Running all builds as serial operations is a non-starter. Bonus points for being able to distribute them across multiple hosts.
  • Having to implement a pile of shell script outside of bitbake to make this work means you’re doing it wrong. The script that automates this build should be doing little more than calling bitbake.

First things first: my solution isn’t perfect. It does work pretty well though and achieves much of the above. Below is a quick visual of what I intend for the end product to support:

rootfs image relationships

On the left is the simple case I’m working to support currently. The boxes represent the root file systems (rootfs) that bitbake is churning out. The lines pointing from one rootfs to another represent one rootfs being packaged in another. dom0 here would be a live image and it would boot the NDVM automatically. Naturally the NDVM rootfs must be contained within dom0 for this to work. The right hand side is an eventual goal.

To support what most people think of as a ‘distro’ you need an installer to lay things down on a physical disk and if users expect to be able to run arbitrary workloads / VMs then they’ll want the whole disk available. In this scenario the installer image rootfs will have the image packages for the VMs installed in it (including dom0!). The installer when do it’s thing laying dom0 down in a partition but it can also drop the supporting VMs images into another partition. After installation, dom0 is booted from physical media and it will be able to boot these supporting VMs.

Notice the two level hierarchical relationship between the rootfs images in the diagram. The rootfs’ on the lower part of the diagram are completely independent and thus can be built in parallel. This will make them easily distributed across multiple build systems. Now on to some of the methods I tried to realize this goal and eventually one that worked!

Changing DISTRO in a build tree

The first thing I played around with was rewriting my local.conf between image builds to change the DISTRO. I use a different DISTRO configs to make package customizations that differentiate my images. This would allow me to add a simple IMAGE_POSTPROCESS_COMMAND to copy service VM rootfs images into the outer image (again, dom0 or an installer).

I had hoped I’d be able to pull this off and just have bitbake magically pick up the differences so I could build multiple images in the same build tree. This would make my image builds serial but possibly very efficient. This caused several failures in my tests however so I decided it would be best to keep separate builds for my individual images. I should probably find the right mailing lists to help track down the root cause of this but I expect this is well outside of the ‘supported’ bitbake / OE use cases.

Copying data across build trees

As a fall-back I came up with a hack in which I copy the needed build artifacts (rootfs & kernel image) to a common location as a post processing step in the image recipe. I’ve encapsulated this in a bbclass in anticipation of using the same pattern for other VM images. I’ve called this class integral-image-export.bbclass:

inherit core-image

do_export() {
    manifest_install() {
        if [ ! -z "$1" ]; then
            install -m 0644 "$1" "$4"
            printf "%s *%sn" "$(sha256sum --binary $1 | awk '{ print $1 }')" "$2" >> $3

    # only do export if export dir is defined
    if [ ! -z "${INTEGRAL_EXPORT_DIR}" ]; then
        ROOT="${INTEGRAL_EXPORT_DIR}/${PN}-$(date --utc +%Y-%m-%dT%H:%M:%S.%NZ)"
        mkdir -p ${ROOT}
        manifest_install "${KERN_PATH}" "${KERN_FILE}" "${MANIFEST}" "${ROOT}"
        manifest_install "${ROOTFS}" "${FS_FILE}" "${MANIFEST}" "${ROOT}"

addtask export before do_build after do_rootfs

It lives here So by having my NDVM image inherit this class, and properly defining the INTEGRAL_EXPORT_DIR in my builds local.conf, the NDVM image recipe will copy these build artifacts out of the build tree.

Notice that the destination directory has an overly precise time stamp as part of its name. This is an attempt to create unique identifiers for images without having to track incrementing build numbers. Also worth noting is the manifest_install function. Basically this generates a file in the same format as the sha*sum utilities with the intent of those programs being able to verify the manifest.

Eventually I think it would be useful for a manifest to contain data about the meta layers that went into building the image and the hashes of the git commit checked out at the time of the build. This later bit will be useful if a build ever has to be recreated. Not something that’s necessary yet however.

Consuming exported images

After exporting these build artifacts we have to cope with other images that want to consume them. My main complaint about using a build script outside of my built tree to place images within one another is that I’d have to re-size existing file systems. Bitbake already builds file systems so resizing them from an external script seemed very ugly. Further changes to the images built by bitbake (ext3/iso/hddimg etc) would have to be coordinated with said external script. Very ugly indeed.

The most logical solution was to create a new recipe as a way to package the existing build artifacts into a package that can be consumed by an image. By ‘package’ I mean your typical ipk or rpm. This allows bitbake to continue to do all of the heavy lifting in image building for us. Assuming the relationships between images shown above, it allows the outer image to include the image package using the standard IMAGE_INSTALL mechanism. That feels borderline elegant compared to rewriting the generated file systems IMHO.

So from the last section we have builds that are pumping out build artifacts and for the case of our example we’ll say they land in /mnt/integral/image-$stamp where $stamp is a unique time stamp. On the other hand we need to create a recipe that consumes the artifacts (I’ll call it an ‘image package recipe’ from here out) in these directories. Typically in a bitbake recipe you’ll provide a URI to your source code in the SRC_URI variable and define the files that go into the image using FILES_${PN}. These are generally defined statically in the recipe. Our case is weird in that we want the image package recipe to grab the latest image exported by some other build. So we must dynamically generate these variables.

Though I’ve never seen these variables generated dynamically (aside from using the PN and PV variables in URIs) but it’s surprisingly easy. bitbake supports anonymous python functions that get run when the recipe is parsed. This happens before any tasks are executed so setting SRC_URI and PV in this function works quite well. The method for determining the latest images that our build has exported is a simple directory listing and sorting operation:

python() {
    import glob, os, subprocess

    # check for valid export dir
        bb.note ('INTEGRAL_EXPORT_DIR is empty')
        return 0
    if not os.path.isdir (INTEGRAL_EXPORT_DIR):
        bb.fatal ('INTEGRAL_EXPORT_DIR is set, but not a directory: {0}'.format (INTEGRAL_EXPORT_DIR))
        return 1

    PN = d.getVar ('PN', True)
    LIBDIR = d.getVar ('libdir', True)
    XENDIR = d.getVar ('XENDIR', True)
    VMNAME = d.getVar ('VMNAME', True)

    # find latest ndvm and verify hashes
    IMG_NAME = PN[:PN.rfind ('-')]
    DIR_LIST = glob.glob ('{0}/{1}*'.format (INTEGRAL_EXPORT_DIR, IMG_NAME))
    DIR_LIST.sort (reverse=True)
    DIR_SAVE = os.getcwd ()
    os.chdir (DIR_LIST [0])
        DEV_NULL = open ('/dev/null', 'w')
        subprocess.check_call ('sha256sum -c manifest', stdout=DEV_NULL, shell=True)
    except subprocess.CalledProcessError:
        return 1
        DEV_NULL.close ()
        os.chdir (DIR_SAVE)

    # build up SRC_URI and FILES_${PN} from latest NDVM image
    d.appendVar ('SRC_URI', 'file://{0}/*'. format (DIR_LIST [0]))
    d.appendVar ('FILES_{0}'.format (PN), ' {0}/{1}/{2}/*'.format (LIBDIR, XENDIR, VMNAME))

    # set up ${S}
    WORKDIR = d.getVar ('WORKDIR', True)
    d.setVar ('S', '{0}/{1}'.format (WORKDIR, DIR_LIST [0]))
    return 0

If you’re interested in the full recipe for this image package you can find it here:

The ‘manifest’ described above is also verified and processed. Using the file format of the sha256sum utility is a cheap approximation of the OE SRC_URI[sha256sum] metadata. This is a pretty naive approach to finding the “right” image to package as it doesn’t give the outer image much say over which inner image to pull in: It just grabs the latest. Some mechanism for the consuming image to specify which image it consumes would be useful.

So that’s about it. I’m pretty pleased with the outcome but time will tell how useful this approach is. Hopefully I’ll get a chance to see if it scales well in the future. Throw something in the comments if you get a chance to play around with this or have thoughts on the topic.

OE image package

Here’s a fun problem that I don’t yet have a solution to: I want to build a single image with OE. This image will be my dom0. I want to include other images in this image. That is to say I want to package service VMs as part of / in my dom0.

All of the research I’ve done up till now (all 30 minutes of it) points to this having never been done before. I could be using the wrong keywords but I the ones I tried turned up nothing on the respective OE and Yocto mailing lists. There seem to be a huge number of pitfalls here including things like changing the DISTRO_FEATURES in effect for the images as well as selecting image specific files for packages. On a few occasions I’ve used the distro name as a way to select specific configuration files like an fstab or interfaces.

What I want is to run bitbake once for the dom0 image and have it build all the other images and install them as packages in dom0. So I’d need to have recipes that actually package the images so they can be installed in another image. I think that will be the easy part.

The hard part will be making packages specific to each image with different files specific to the image. The only thing I can come up with for this is to play ugly tricks like building each VM image with a different MACHINE type but I’m not even sure if that will work. I guess all I can do for now is to experiment a bit and get on the mailing list to make sure I’m not duplicating work that’s already been done. This could get ugly.

Measured Launch on OE core

It’s been 4 months since my last post but I’ve been working on some fun stuff. Said work has progressed to the point where it’s actually worth talking about publically so I’m crawling out from under my favorite rock and putting it “out there”.

My last few bits of writing were about some random OpenEmbedded stuff, basically outlining things I was learning while bumbling my way through the OE basics. I’ve been reading through the meta-selinux and meta-virtualization layers and they’re a great place to learn. Over the winter Holiday here I had some extra vacation time from my day job to burn so I finally got serious about a project I’ve been meaning to start for way too long.


Over the past year I’ve been thinking a lot about the “right way” to measure a software system. We’ve implemented a measurement architecture on XT but this has a few down sides: First a system as large as XT is very difficult to use as a teaching tool. It’s hard to explain and show someone the benefits of measuring a system when your example is large, complex and the relevant bits are spread throughout the whole system. Even our engineers who know our build system inside and out often get lost in the details. Second the code belongs to Citrix and closed source software isn’t very useful to anyone except the people selling it.

So after reading through the meta-selinux and meta-xen layers a bunch and learning a good bit about writing recipes I’ve started work on a reference image for a “measured system”. I’m keeping the recipes that make up this work in a layer I call ‘meta-measured’. For this first post on the topic of measured systems I’ll stick to discussing the basic mechanics of it’s construction. This includes some data on the supporting recipes and some of the component parts necessary for booting it. Hopefully along the way I’ll be able to justify the work by discussing the potential benefits to system security but the theory and architecture discussions will be left for a later post.

get the source

If you’re interested in just building it and playing with the live image this is where you should start. Take a look and let me know what you think. Feedback would be much appreciated.

All of the work I’ve done to get this first bootable image working is up on my github. You can get there, from here: The ‘meta-measured’ layer is here: To automate setting up a build environment for this I’ve got another repo with a few scripts to checkout the necessary supporting software (bitbake / OE / meta-intel etc), a local.conf (which you may need to modify for your environment), and a script to build the ‘iso’ that can be written to a USB drive for booting a test system:

The best way to build this currently is to checkout the measured-build-scripts repo:

git clone git://

run the ‘’ script to populate the required git submodules and to clone the meta-measured layer:

cd measured-build-scripts

build the iso

If you try to run the ./ script next as you would think you should, the build will fail currently. It will do so while attempting to download the SINIT / ACM module for TXT / tboot because Intel hides the ACMs behind a legal terms wall with terms that must be accepted before the files can be downloaded. I’ve put the direct link to it in the recipe but the download fails unless you’ve got the right cookie in your browser so wget blows up. Download it yourself from here:, then drop the zip into your ‘download’ directory manually. I’ve got the local.conf with DL_DIR hardwired to /mnt/openembedded/downloads so you’ll likely want to change this to suit your environment.

Anyway I’ll sort out a way to fool the Intel lawyer wall eventually … I’m tempted to mirror these files since the legal notice seems to allow this but I don’t really have the bandwidth ATM. Once you’ve got this sorted, run the script. I typically tee the output to a file for debugging … this is some very ‘pre-alpha’ stuff so you should expect to debug the build a bit 🙂

./ | tee build.log

This will build a few images from the measured-image-bootimg recipe (tarballs, cpios, and an iso). The local.conf I’ve got in my build directory is specific to my test hardware so if you’ve got an Intel SugarBay system to test on then you can dump the ISO directly to a USB stick and boot it. If you don’t have a SugarBay system then you’ll have to do some work to get it booting since this measured boot stuff is closely tied to the hardware, though the ACMs I’ve packaged work for 2nd and 3rd gen i5 and i7 hardware (Sandy and Ivy Bridge).


I’ve organized the recipes that make up this work into two categories: Those that are specific to the TPM and those that are specific to TXT / tboot. Each of these two technologies requires some kernel configs so those are separated out into fragments like I’ve found in other layers. My test hardware has USB 3.0 ports which the base OE layers don’t seem to have yet. I’ve included this config in my oe-measured distro just so I can use the ports on the front of my test system.

The TPM recipes automate building the Trousers daemon, libtspi and some user space tools that consume the TSS interface. Recipes for the TPM software are pretty straight forward as most are autotools projects. Some work was required to get the trousers project separated into packages for the daemon and library.

The tboot recipes were a bit more work because tboot packages a bunch of utilites in the main tboot source tree so they had to be separated out into different packages (this work is still on-going). Further tboot doesn’t use autotools and they squash most compiler flags that the OE environment passes in. The compler flags required by tboot are static which stands at odds with OE and a cross-compiled environment that wants to change the path to everything including the compiler.

I’ve no clue if tboot will build properly on anything other than an Intel system. Further the issue of Intel hiding the ACMs required for their chipssets behind an EULA wall is annoying as the default OE fetcher won’t work.


My first instinct is always to to describe a system by construction: from the bottom up. In this case I think going top-down is a better approach so we’ll start with the rootfs and work backwards. The TPM recipes includes two images based on the core-image from OE core. That’s one initramfs image and one rootfs. The rootfs is just the core-image with the TPM kernel drivers, trousers daemon, tpm-tools and the tpm-quote-tools. I haven’t done much with this rootfs other than booting it up and see if TXT and the TPM works as expected.

There’s also an initramfs with the TPM kernel drivers, trousers daemon and the tpm-tools but not the quote tools. This is a very minimal initramfs with the TSS daemon loaded manually in the initrd script. It’s not expected that users will be using the tpm-tools interactively here but that’s what I’ve been doing for initial testing. Only the tpm_extendpcr tool (open source from Citrix) is used to extend a PCR with the sha1sum hash of the rootfs before the call to switch_root. This requires that the ‘coreutils’ package be included just for the one utility which bloats the initramfs unfortunately. Slimming this down should’t be too much work in the future. Anyway I think this is ‘the right way’ to extend the measurement chain from the initramfs up to the rootfs of the system.

The rest of the measruements we care about are taken care of by the components from the TXT recipes. There’s only one image in the TXT recipe group however. This is derived from the OE core live image and it’s intended to be ‘deployable’ in the lanugage of OE recipes. I think this means an hddimg or an ISO image, basically something you can ‘dd’ to disk and boot. Currently it’s the basis for a live image but could easily be used for something like an installer simply by switching out the rootfs.

This image is not a separate root filesystem but instead it’s an image created with the files necessary to boot the system: syslinux (configured with the mboot.c32 comboot module), tboot, acms and the initrd and the rootfs from the TPM recipes. tboot measures the bootloader config, all of the boot modules and a bunch of other stuff (see the README in the tboot sources for details). It stores these measurements in the TPM for us, creating the ‘dynamic root of trust for measurement’ (DRTM).

Once tboot has measured all of the modules, the initramfs takes over. The initramfs then measures the rootfs as described above before the switch to root. I’ve added a few kernel parameters to pass the name of the rootfs and the PCR where it’s measurement is to be stored.

If the rootfs is measured on each boot it must be mounted read-only to prevent its measurement from changing … yup even mounting a journaled file system read-write will modify the journal and change the filesystem. Creating a read-only image is a bit of work so for this first prototype I’ve used a bit of a short cut: I’ve mounted the rootfs read only, create a ramfs read write, then the two are combined in a unionfs. In this configuration when rootfs boots it looks like a read / write mount. Thus on each boot the measurements in the TPM are the same.

Next Steps

Measuring a system is all well and good but who cares? Measurements are only useful when they’re communicated to external parties. For now this image only takes measurements and these measurements are the same on each boot. That’s it. Where this can be most immediately useful is that these measurements can be predicted in the build.

The PCRs 0-7 are reserved for the BIOs and we have no way of predicting these values currently as they’re unique to the platform and that’s messy. The tboot PCRs however (17, 18 and 19 in the Legacy mapping currently used) can be calculated based on the hashing done by tboot (read their docs and The PCR value containing the measurement of the rootfs can be calculated quite simply as well.

For a reference live image this is interesting only in an academic capacity. As I suggest above, this image can be used as a template for something like an installer which would give the predictability of PCR values much deeper meaning: Consider an installer architecture where the installer itself is a very small rootfs that downloads the install package from a remote server (basically Debian’s netboot iso or a PXE boot setup). Assuming we have a method for exchanging system measurements (more future work) it would be very useful for the remote server to be able to evaluate measurements from the installer before releasing the install package.

This is probably a good place to wrap up this post. The meta-measured layer I’ve described is still very new and the images I’ve built are still usefuly only for ‘tire-kicking’. My next post will hopefully discuss predicting measurement values in the build system and other fun stuffs.

openembedded yocto native hello world

NOTE: I took the time to get to the bottom of the issue discussed in this post. There’s a new post here that explains the “right way” to use Makefiles with yocto. As always, the error in this post was mine 🙂

I’ve officially “drank the Kool-Aid” and I’m convinced openembedde and Yocto are pretty awesome. I’ve had a blast building small Debian systems on PCEngines hardware in the past and while I’m waiting for my Raspberry Pi to arrive I’ve been trying to learn the ins and outs of Yocto. The added bonus is that the XenClient team at Citrix uses openembedded for our build system so this work can also fall under the heading of “professional development”.

Naturally the first task I took on was way too complicated so I made a bunch of great progress (more about that in a future post once I get it stable) but then I hit a wall that I ended up banging my head against for a full day. I posted a cry for help on the mailing list and didn’t get any responses so I set out to remove as many moving parts as possible and find the root cause.

First things first read the Yocto development manual and the Yocto reference for whatever release you’re using. This is essential because no one will help you till you’ve read and understand these 🙂

So the software I’m trying to build is built using raw Makefiles, none of that fancy autotools stuff. This can be a bit of a pain because depending on the Makefiles, it’s not uncommon for assumptions to be made about file system paths. Openembedded is all about cross compiling so it wants to build and install software under all sorts of strange roots and some Makefiles just can’t handle this. I ran into a few of these scenarios but nothing I couldn’t overcome.

Getting a package for my target architecture wasn’t bad but I did run into a nasty problem when I tried to get a native package built. From the searches I did on the interwebs it looks like there have been a number of ways to build native packages. The current “right way” is simply to have your recipe extend the native class. Thanks to XorA for documenting his/her new package workflow for that nugget.


After having this method blow up for my recipe I was tempted to hack together some crazy work around. I really want to upstream the stuff I’m working on though and I figure having crazy shit in my recipe to work around my misunderstanding of the native class was setting the whole thing up for failure. So instead I went back to basics and made a “hello world” program and recipe (included at the end of this post) hoping to recreate the error and hopefully figure out what I was doing wrong at the same time.

It took a bit of extra work but I was able to recreate the issue with a very simple Makefile. First the error message:

NOTE: package hello-native-1.0-r0: task do_populate_sysroot: Started
ERROR: Error executing a python function in /home/build/poky-edison-6.0/meta-test/recipes-test/helloworld/
CalledProcessError: Command 'tar -cf - -C /home/build/poky-edison-6.0/build/tmp/work/i686-linux/hello-native-1.0-r0/sysroot-destdir///home/build/poky-edison-6.0/build/tmp/sysroots/i
686-linux -ps . | tar -xf - -C /home/build/poky-edison-6.0/build/tmp/sysroots/i686-linux' returned non-zero exit status 2 with output tar: /home/build/poky-edison-6.0/build/tmp/work
/i686-linux/hello-native-1.0-r0/sysroot-destdir///home/build/poky-edison-6.0/build/tmp/sysroots/i686-linux: Cannot chdir: No such file or directory
tar: Error is not recoverable: exiting now
tar: This does not look like a tar archive
tar: Exiting with failure status due to previous errors

ERROR: The stack trace of python calls that resulted in this exception/failure was:
ERROR:   File "sstate_task_postfunc", line 10, in 
ERROR:   File "sstate_task_postfunc", line 4, in sstate_task_postfunc
ERROR:   File "sstate.bbclass", line 19, in sstate_install
ERROR:   File "/home/build/poky-edison-6.0/meta/lib/oe/", line 59, in copytree
ERROR:     check_output(cmd, shell=True, stderr=subprocess.STDOUT)
ERROR:   File "/home/build/poky-edison-6.0/meta/lib/oe/", line 121, in check_output
ERROR:     raise CalledProcessError(retcode, cmd, output=output)
ERROR: The code that was being executed was:
ERROR:      0006:, d)
ERROR:      0007:    sstate_package(shared_state, d)
ERROR:      0008:
ERROR:      0009:
ERROR:  *** 0010:sstate_task_postfunc(d)
ERROR:      0011:
ERROR: (file: 'sstate_task_postfunc', lineno: 10, function: )
ERROR:      0001:
ERROR:      0002:def sstate_task_postfunc(d):
ERROR:      0003:    shared_state = sstate_state_fromvars(d)
ERROR:  *** 0004:    sstate_install(shared_state, d)
ERROR:      0005:    for intercept in shared_state['interceptfuncs']:
ERROR:      0006:, d)
ERROR:      0007:    sstate_package(shared_state, d)
ERROR:      0008:
ERROR: (file: 'sstate_task_postfunc', lineno: 4, function: sstate_task_postfunc)
ERROR: Function 'sstate_task_postfunc' failed
ERROR: Logfile of failure stored in: /home/build/poky-edison-6.0/build/tmp/work/i686-linux/hello-native-1.0-r0/temp/log.do_populate_sysroot.30718
Log data follows:
| NOTE: QA checking staging
| ERROR: Error executing a python function in /home/build/poky-edison-6.0/meta-test/recipes-test/helloworld/
| CalledProcessError: Command 'tar -cf - -C /home/build/poky-edison-6.0/build/tmp/work/i686-linux/hello-native-1.0-r0/sysroot-destdir///home/build/poky-edison-6.0/build/tmp/sysroots
/i686-linux -ps . | tar -xf - -C /home/build/poky-edison-6.0/build/tmp/sysroots/i686-linux' returned non-zero exit status 2 with output tar: /home/build/poky-edison-6.0/build/tmp/wo
rk/i686-linux/hello-native-1.0-r0/sysroot-destdir///home/build/poky-edison-6.0/build/tmp/sysroots/i686-linux: Cannot chdir: No such file or directory
| tar: Error is not recoverable: exiting now
| tar: This does not look like a tar archive
| tar: Exiting with failure status due to previous errors
| ERROR: The stack trace of python calls that resulted in this exception/failure was:
| ERROR:   File "sstate_task_postfunc", line 10, in 
| ERROR:   File "sstate_task_postfunc", line 4, in sstate_task_postfunc
| ERROR:   File "sstate.bbclass", line 19, in sstate_install
| ERROR:   File "/home/build/poky-edison-6.0/meta/lib/oe/", line 59, in copytree
| ERROR:     check_output(cmd, shell=True, stderr=subprocess.STDOUT)
| ERROR:   File "/home/build/poky-edison-6.0/meta/lib/oe/", line 121, in check_output
| ERROR:     raise CalledProcessError(retcode, cmd, output=output)
| ERROR: The code that was being executed was:
| ERROR:      0006:, d)
| ERROR:      0007:    sstate_package(shared_state, d)
| ERROR:      0008:
| ERROR:      0009:
| ERROR:  *** 0010:sstate_task_postfunc(d)
| ERROR:      0011:
| ERROR: (file: 'sstate_task_postfunc', lineno: 10, function: )
| ERROR:      0001:
| ERROR:      0002:def sstate_task_postfunc(d):
| ERROR:      0003:    shared_state = sstate_state_fromvars(d)
| ERROR:  *** 0004:    sstate_install(shared_state, d)
| ERROR:      0005:    for intercept in shared_state['interceptfuncs']:
| ERROR:      0006:, d)
| ERROR:      0007:    sstate_package(shared_state, d)
| ERROR:      0008:
| ERROR: (file: 'sstate_task_postfunc', lineno: 4, function: sstate_task_postfunc)
| ERROR: Function 'sstate_task_postfunc' failed
NOTE: package hello-native-1.0-r0: task do_populate_sysroot: Failed
ERROR: Task 3 (virtual:native:/home/build/poky-edison-6.0/meta-test/recipes-test/helloworld/, do_populate_sysroot) failed with exit code '1'
ERROR: 'virtual:native:/home/build/poky-edison-6.0/meta-test/recipes-test/helloworld/' failed

So even with the most simple Makefile I could cause a native recipe build to blow up. Here’s the Makefile:

.PHONY : all clean install uninstall


HELLO_src = hello.c
HELLO_bin = hello
HELLO_tgt = $(BINDIR)/$(HELLO_bin)

all : $(HELLO_bin)

$(HELLO_bin) : $(HELLO_src)

$(HELLO_tgt) : $(HELLO_bin)
	install -d $(BINDIR)
	install -m 0755 $^ $@

clean :
	rm $(HELLO_bin)

install : $(HELLO_tgt)

uninstall :
	rm $(BINDIR)/$(HELLO_tgt)

And here’s the relevant install method from the bitbake recipe:

do_install () {
    oe_runmake DESTDIR=${D} install

Notice I’m using the variable DESTDIR to tell the Makefile the root (not just /) to install things to. This should work right? It works for a regular package but not for a native one! This drove me nuts for a full day.

The solution to this problem lies in some weirdness in the Yocto native class when combined with the populate_sysroot method. The way I figured this out was by inspecting the differences in the environment when building hello vs hello-native. When building the regular package for the target architecture variables like bindir and sbindir were what I would expect them to be:


but when building hello-native they get a bit crazy:


This is a hint at the source of crazy path that staging is trying to tar up above in the error message. Further if you look in the build directory for a regular target arch package you’ll see your files where you expect in ${D}sysroot-destdir/usr/bin but for a native build you’ll see stuff in ${D}sysroot-destdir/home/build/poky-edison-6.0/build/tmp/sysroots/i686-linux/usr/bin. Pretty crazy right? I’m sure there’s a technical reason for this but it’s beyond me.

So the way you can work around this is by telling your Makefiles about paths like bindir through the recipe. A fixed do_install would look like this:

do_install () {
    oe_runmake DESTDIR=${D} BINDIR=${D}${bindir} install

For more complicated Makefiles you can probably specify a PREFIX and set this equal to the ${prefix} variable but YMMV. I’ll be trying this out to keep my recipes as simple as possible.

If you want to download my example the recipe is here. This will pull down the hello world source code and build the whole thing for you.

OE-Core Yocto gcc timeout

I’ve been thrashing around trying to get the upstream OE to build an image for me. Today I finally made a concerted effort over a few hours to dive deep and do this right. It turns out I was using the “old” OE repos when I should have been using the “new” build system from the Yocto Project. Their documentation is excellent but still, my first build failed.

What’s this? The GCC recipe failing because of a network timeout? Oddly enough it actually downloaded some of the sources but not all of ’em.

| svn: REPORT of '/svn/gcc/!svn/vcc/default': Could not read response body: connection was closed by server (
NOTE: package gcc-cross-initial-4.6.1+svnr175454-r10: task do_fetch: Failed
ERROR: Task 5 (/home/build/poky-edison-6.0/meta/recipes-devtools/gcc/, do_fetch) failed with exit code '1'
ERROR: '/home/build/poky-edison-6.0/meta/recipes-devtools/gcc/' failed

At this point I just tried again and it failed in the same place but had checked out more of the code. A quick search turns up a similar error is common when checking out code from SVN servers over HTTP. Apache just has a tendency to timeout when checking out large repositories with mod-svn. The suggested fix is to increase the timeout value in your Apache configs … except these configs are on the GNU web servers and we can’t change them.

What we can change though is the protocol bitbake uses when getting the sources. Just change the proto from ‘http’ to ‘svn’ in the SRC_URI in (found at /meta/recipes-devtools/gcc/ and we’re almost good. It’ll look like this when you’re done.

SRC_URI = "svn://;module=${BRANCH};proto=svn

It still timed out for me a few times but it ran for much longer than the HTTP protocol option. HTTP timed out after about 10 minutes, SVN made it almost an hour before timing out … You’d think there would be a tarball of these sources mirrored somewhere so we didn’t have to kill the GNU SVN servers on every fresh build. Something to look into I guess. Either way gcc is building now, hopefully I’ll have a build running soon …

UPDATE: With some advice from Scott below I used the poky distro by including: DISTRO="poky" in my local.conf file. As promised bitbake then doesn’t try to check out the gcc svn repository directly from Instead it grabs a tarball from one ob the Yocto mirrors and the build takes mere minutes. Thanks Scott!