Unikraft releases v0.13.0 (Atlas)

In this blog post, we describe some of the new features available in Unikraft.

Unikraft v0.13.0 (Atlas) is out!

As usual, this release adds important fixes and comes with a bunch of new features!

In this blog post, we describe some of the new features available in Unikraft. For a full breakdown, please check out the changelog.

New Synchronization Primitives (#476)#

This feature began as a Google Summer of Code 2022 (GSoC22) project, and it was championed by Sairaj Kodilkar under the guidance of Marc Rittinghaus and Andra Paraschiv with support from Radu Nichita and Răzvan Deaconescu.

The release introduces an IRQ-safe API for spinlocks as well as an SMP-safe mutex and semaphore implementation. Previously, mutexes and semaphores only disabled interrupts for synchronization, which limited these primitives to uniprocessor systems. The new SMP-safe implementation uses atomic operations and spinlocks instead, making them ready for use in multicore environments. This is an important step towards full multicore support in Unikraft and part of our effort to introduce proper synchronization to the various Unikraft core libraries and subsystems. Along with this improvement, mutexes are changed to be non-recursive by default; this is to discourage the use of recursive synchronization, which usually increases complexity and is an indication of poor design. In addition, this allows possible future optimizations of the mutex implementation.

While correct synchronization is a complex topic in and of itself, achieving good performance scalability with increasing numbers of cores is even more challenging. To this end, developers need to be able to choose from a wide range of synchronization methods and SMP-safe data structures. This release adds SMP-safe reader-writer locks to uklock's repertoire of synchronization primitives. Reader-writer locks control access to a shared resource by allowing multiple readers or a single writer at a time, ensuring concurrent read operations and exclusive write operations. Employing reader-writer locks is thus more efficient for sychronizing data structures that, on average, experience more parallel reads than writes, for example when iterating over a list of virtual memory areas to resolve page faults.

More information on the changes related to synchronization in Unikraft can be found here:

Native Firecracker VMM Support (#760)#

This feature was championed by Marco Schlumpp with important input from Marc Rittinghaus, Sergiu Moga and Andrei Topala.

⚠️ This addition results in a breaking change to Unikraft's output binary artifact name.

This release introduces support for booting Unikraft on the Firecracker VMM. Compared to QEMU, this enables even faster boot times for Unikraft unikernels. This support was built on top of the boot code refactoring in the previous release, and therefore shares most of the code with the multiboot entry point used with QEMU.

Please note that currently Unikraft's virtio drivers do not work with Firecracker. This will be addressed with a future release.

Previously, when building for x86_64 and targeting KVM, the resulting binary artifact would be output, in the case of the helloworld application, as helloworld_kvm-x86_64. The new artifact name now includes the target VMM, so the result will be helloworld_qemu-x86_64, or helloworld_fc-x86_64 in the case of Firecracker.

posix-environ: Handling Environmental Variables (#868)#

This feature was championed by Simon Kuenzer with support from Răzvan Deaconescu, Eduard Mihăilescu and Job Paardekooper.

This release introduces the handling of environment variables with the posix-environ library. The environment variables vector environ can be populated at compile time and at runtime if uklibparam is configured as part of a build. The library provides POSIX-conformant getters and setters, like getenv() and setenv().

The variables provided at compile-time are configurable with make menuconfig under Library Configuration --> posix-environ --> Compiled-in environment variables. 16 slots are available and the initial environ vector is created with the filled slots.

Additionally, the configuration option Parse kernel command line arguments enables setting further initial environment variables via the kernel command line. In this mode, the parameter env.vars accepts an array of strings that is appended to the compile-time initialized vector.

As example, the following command line snippet sets the variables PATH, UID, GID, and LD_LIBRARY_PATH=/lib:

env.vars=[ "PATH=/bin" "UID=0" "GID=0" "LD_LIBRARY_PATH=/lib" ] --

Rewriting uklibparam (#867)#

This feature was championed by Simon Kuenzer with input from Alexander Jung and Răzvan Deaconescu.

Unikraft's library parameter parser was originally rewritten to provide support for environment variables via the kernel command line (see posix-environ).

Besides ensuring an allocation-free and TLS-free implementation for early boot code, uklibparam now relies on pre-processed argument vectors, as with ukargparse. This avoids duplicated processing of quotes while naturally enabling support for single quotes ('), double quotes ("), and nested quoting. Also, arrays of strings are supported by this release.

A new set of registration macros simplifies the registration process and introduces the ability to specify a description that is displayed with the help kernel command:

Usage of command line:
Special commands:
help Print this help summary
Available parameters:
env.vars Environment variables (array[8] of charp)
vfs.rootfs rootfs (charp)
vfs.rootdev rootdev (charp)
vfs.rootopts rootopts (charp)
vfs.rootflags rootflags (u64)
Numbers can be passed in decimal, octal ("0" as prefix), or hexadecimal ("0x" as prefix).
Valid boolean values for 'true' are: "true", "on", "yes", a non-zero number.
Valid boolean values for 'false' are: "false", "off", "no", a zero number (e.g., "0").
Boolean parameters that are passed without a value will be set to 'true'.
Array parameters can be passed with multiple 'PREFIX.PARAMETER=VALUE' tokens,
using a list: 'PREFIX.PARAMETER=[ VALUE0 VALUE1 ... ]', or a combination of both.
Please refer to the application manual or application help for application arguments.

To use this, a library only needs to include uk/libparam.h, declare the variables, and register those with uklibparam. The following example demonstrates how this is done with C code:

#include <stddef.h> /* NULL */
#include <uk/libparam.h>
/* Declarations with default values */
static char *myvar="My parameter";
static char *myvec[4]={ NULL };
/* Registration to uklibparam
* NOTE: The macro automatically removes the registration if
* lib/uklibparam is excluded from the configuration.
UK_LIBPARAM_PARAM(myvar, charp, "My variable");
UK_LIBPARAM_PARAM_ARR(myvar, charp, 4, "My C-string vector");

The following command line snippet sets the variables myvar and myvec:

mylib.myvar="Banana" mylib.myvec=[ "I" "am" "very" "hungry!" ] --

Alternatively, arrays can be filled with multiple tokens or a combination of array syntax and tokens; for example:

mylib.myvar="Banana" mylib.myvec="I" mylib.myvec="am" mylib.myvec=[ "very" "hungry!" ] --

app-elfloader Updates#

This work was championed by Simon Kuenzer with extensive support from Andra Paraschiv, Cosmin Vancea and Răzvan Deaconescu.

This release includes updates that enhance and simplify the use of app-elfloader. app-elfloader is used to run unmodified Linux ELFs with Unikraft, via the syscall_shim.

The file has been updated with detailed instructions on configuring, building, running and debugging app-elfloader. A helper debugger script allows the use of debugging symbols in the application, in the loader and in the standard C library.

For dynamic applications, explicit loading of the Linux dynamic linker / loader was required. Recent updates don't require that, and the path to the actual dynamic ELF can be passed to the running Unikraft instance. app-elfloader parses the .interp section to obtain information about the dynamic linker / loader, typically located in /lib64/ on a typical Linux system. The dynamic linker / loader, which needs to be part of the filesystem of the running Unikraft instance, is then loaded and invoked to load dependent libraries and to do dynamic symbol resolution.

Up until now, the executable (or the explicit dynamic linker / loader) was passed as part of the initial ramdisk, using the -initrd argument of the qemu-system command. With these recent changes, the executable can be part of the running instance's filesystem. The filesystem path is passed as an argument when running app-elfloader. Finally, executing applications is now simplified by using the companion [run-app-elfloader repository], consisting of wrapper scripts and pre-built images.

Application Compatibility Updates#

The work under this banner is the result of continuous effort from Marc Rittinghaus, Simon Kuenzer, Răzvan Deaconescu, Ioan Țeugea, Florin Postolache, Andra Paraschiv, Marco Schlumpp and Cosmin Vancea.

Multiple applications are tested using the binary-compatibility mode, i.e. running unmodified Linux ELFs on top of Unikraft, by trapping in the Unikraft syscall_shim; this is done using app-elfloader. ELFs must be PIE (Position-Independent Executables). Two repositories store pre-built applications: dynamic-apps and static-pie-apps, for dynamic and static PIE apps, respectively.

Running these applications revealed (1) incompatibilities between the Linux ABI expected by applications and Unikraft and (2) incomplete, missing or faulty system calls; both issues are now fixed. Applications in the dynamic-apps and static-pie-apps repositories are now working with Unikraft by employing app-elfloader.

As part of the effort, the dynamic-apps repository was created. And the static-pie-apps repository was enriched with new applications. Focus is on dynamic PIE apps, since they are the default applications on Linux distributions; they can simply be picked up, together with dependent libraries, configuration files and support files, and provided inside a filesystem to be run with Unikraft by using app-elfloader.

Existing applications can be quickly tested by using the companion run-app-elfloader repository:

$ ./
Usage: ./ [-l] <app>
Possible apps:
bc bc_static bzip2 client client_go client_go_static client_static echo gzip
gzip_static haproxy helloworld helloworld_cpp helloworld_cpp_static
helloworld_go helloworld_go_static helloworld_rust helloworld_rust_static_gnu
helloworld_rust_static_musl helloworld_static ls nginx nginx_static openssl
python redis redis7 redis_static server server_go server_go_static
server_static sqlite3 sqlite3_static
-l - use dynamic loader explicitly
$ ./ helloworld
Hello, World!

Newlib Support in the Latest Unikraft Version#

This feature was championed by Eduard Vintilă, with support from Maria Sfîrăială, Răzvan Deaconescu and Teodor Țeugea.

Since the introduction of Musl as the default standard C library (libc) for Unikraft, in release 0.11.0, Newlib support was deprioritized. With this release, Newlib support is now updated to the most recent Unikraft version.

Updates to lib-newlib and to the companion threading library lib-pthread-embedded were related to the recent updates of Unikraft and lib-lwip: new scheduling API, Musl-imported functions, timing.

Most Unikraft application repositories are currently configured to use, by default, Musl, though they can be configured to use Newlib instead.

Documentation Updates#

This feature was championed by Ștefan Jumărea, with extensive support from Radu Nichita, Maria Sfîrăială, Răzvan Deaconescu, Delia Pavel and Eduard Vintilă.

As usual with every release, we have significantly updated our documentation. Most of the updates have to do with documenting existing features that has little or sometimes no docmentation, and were often driven by support for hatckathon and tutorial events.

Documentation updates are pushed to the core unikraft repository and in the docs repository repos -- the latter also stores website information.

In the core unikraft repository, documentation consists of (1) files in internal libraries, such as vfscore; and (2) Doxygen-style comments in header and source code files, such as ramfs, that are then exported (or will be) to Unikraft's website, as official API documentation.

For the docs repository, most changes consist of updates to hackathon sessions for the hackathons taking place during this time. Two important additions to documentation are related to binary compatibility and to building and running complex applications.

Community Activities#

Full Day Hackathon at UPB in March#

We took the time to do another full day hackathon! The hackathon took place on 11th of March 2023. Everyone interested could join us in-person, at University POLITEHNICA of Bucharest, and online, on our Discord server.

We had all kind of community members joining, from beginners to more experienced people, adding features, reviewing, debugging or making their first steps in Unikraft. And the project provided the all essential pizza :)

Full-day Hackathon at UPB, 2023
Full-day Hackathon at UPB, 2023

Athens Hackathon#

On the 30th and 31st of March 2023, we organized our first hackathon in Greece, with support from Nubificus, the High Speed Communication Networks Lab (HSCN) and the Computing Systems Lab (CSLab) of the National Technical University of Athens (ICCS/NTUA)!

For two days, the participants were introduced to the Unikraft universe and had the opportunity to become part of our community and to submit their first contributions. Michalis Pappas, Răzvan Deaconescu and Ștefan Jumărea provided help on-site, with other senior community members offering online support.

You can find the hackathon sessions and challenges on the Athens Hackathon page.

Athens Hackathon, 2023
Athens Hackathon, 2023

Amsterdam Hackathon#

We continued our hackathon season with the Amsterdam Unikraft Hackathon, organized on the 15th and 16th of April 2023, together with Vrije Universiteit Amsterdam (VUA) and VUSec.

This time, Răzvan Deaconescu was joined by Hugo Lefeuvre on-site, with other community members keeping in touch online.

For full hackathon contents, check the Amsterdam Hackathon page.

Amsterdam Hackathon, 2023
Amsterdam Hackathon, 2023

Porto Hackathon#

The show must go on! We then moved to Porto for the next Unikraft hackathon, organized in collaboration with Faculdade de Engenharia Universidade do Porto and University of Porto Faculty of Engineering ACM Student Chapter. The hackathon took place on Wednesday and Thursday, May 10-11, 2023.

Ștefan Jumărea and Eduard Vintilă were present on-site, with other community members providing support online, on Discord.

You can find more about this on the Porto hackathon page.

Porto Hackathon, 2023
Porto Hackathon, 2023

Google Summer of Code 2023#

The results of the project selection for this year edition of Google Summer of Code are here: 5 projects proposed by Unikraft have been selected!

Here is the list of students that will work together with us in the next few months, together with their projects:

We are looking forward to start mentoring our students, and we can't wait for the great features we are going to develop together!

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