l4-hackers

l4-hackers@os.inf.tu-dresden.de

2827 discussions

CfP: Microkernel and Component-based OS Devroom at FOSDEM 2024
by Martin Decky 15 Nov '23

15 Nov '23

Microkernel and Component-based OS Devroom at FOSDEM 2024 CALL FOR PARTICIPATION On-line version of this CfP: http://fosdem.microkernel.info/ The developers and users of several free and open source microkernel-based, unikernel-based and component-based operating systems will meet as part of FOSDEM 2024 [1] and will share a developer room. The devroom is currently looking for content in the form of talks and other activities related to microkernel-based, unikernel-based, component-based operating systems and similar areas. Possible topics of the devroom include, but are not limited to: * introduction of a specific OS or framework * design of subsystems and the general architecture of an OS * languages, tools and toolchains used * enabling support for hardware (architectures, device drivers) and programming languages * development processes, debugging * maintenance, testing and release engineering * safety, security and robustness * trends and challenges * research and open questions * community and governance * use cases, experiences and status updates * best practices and lessons learned * demos The devroom has been scheduled to Saturday February 3rd 2024 in the afternoon (Central European Time). This is a call for your participation. We kindly ask you to submit your proposals no later than on December 10th 2023 (End of Day, Anywhere on Earth). Please use the pretalx [2] web site to submit your proposals. Note that this is a new submission system and the user accounts from the previous submission system (pentabarf) have not been transferred. Make sure to select the Microkernel and Component-based OS as the track when submitting your proposal and include at least the following information: * title of your proposal * short abstract (one or two paragraphs) * duration (at least 15 minutes and no longer than 40 minutes) * your full name * your short bio You can specify your preferred time slot of your proposal and any other relevant information. The communication language of the devroom is English. Please note that the devroom has been allocated only a half of a day this year. Therefore the final decision on the duration of the talks will be made by the devroom organizers based on the number of accepted proposals. The official devroom schedule (along with the accepted talks) will be announced on December 15th 2023 on the devroom's mailing list [3] and the speakers will be notified via e-mail. The schedule will be published on the FOSDEM web site, too. About the Devroom Since the first Microkernel OS Devroom at FOSDEM 2012 [4], this devroom has been a part of each following FOSDEM (with slight variations of the name). The focus gradually widened to include component-based, unikernel-based and other operating systems. By now, it has become a somewhat institutionalized tradition for the open source operating systems community, a kind of "extended family meeting" and it is one of the places where microkernel and unikernel enthusiasts meet regularly. To this date, over two dozen projects have participated in one way or another. Many of the projects face similar challenges but come up with partially different solutions. Therefore, the goal of the devroom is to bring the various projects together, let them exchange ideas, cross-pollinate and socialize. As every previous year, the devroom will offer the "stage" both to established community members and to newcomers. We like to select the talks in an inclusive manner, while staying true to the main technical topics (system-level software, broadly speaking) and creating a balanced and unbiased schedule. We would like to keep the quality bar of the devroom same as in the previous years. Presenting at FOSDEM implies that the recordings of the talks will be published under Creative Commons license by FOSDEM. By submitting a proposal, the speaker agrees to have the talk made available publicly indefinitely. For organizational purposes, we also need contact information of the speakers of accepted talks. Microkernel Dinner It has also become a habit that the devroom participants dine together somewhere in Brussels. The year 2024 will not be any different, so there is going to be a dinner on Saturday night. We will inform you about the exact arrangements later. About FOSDEM FOSDEM [5] is a two-day conference organized by volunteers to promote the widespread use of free and open source software. FOSDEM is widely recognized as one of the largest and best such events worldwide. FOSDEM covers a wide spectrum of free and open source software and hardware projects and offers a platform for people to collaborate. To this end, FOSDEM has set up developer rooms (devrooms) where teams can meet and showcase their projects. Devrooms are a place for teams to discuss, hack and publicly present latest directions, lightning talks, news and proposals. Besides developer rooms, FOSDEM also offers main tracks, lightning talks, certification exams and project stands. In recent years, FOSDEM has been hosting more than 8000 developers annually at the ULB Solbosch Campus in Brussels, Belgium. The participation in FOSDEM is totally free, although the organizers gratefully accept donations and sponsorship. No registration is necessary. Attendees are expected to follow the FOSDEM's code of conduct [6]. Important Dates Recap * 2023-12-10: Deadline for proposal submission * 2023-12-15: Schedule published and speakers notified of acceptance * 2024-02-03: Devroom taking place Contact For any comments, questions and suggestions, please do not hesitate to use the devroom's mailing list [3] to contact the devroom organizers. The primary organizers of the devroom in 2024 are: * Martin Decky * Razvan Deaconescu References [1] https://fosdem.org/2024/ [2] https://pretalx.fosdem.org/fosdem-2024/cfp [3] https://lists.fosdem.org/listinfo/microkernel-devroom [4] https://archive.fosdem.org/2012/schedule/track/microkernel_os_devroom.html [5] https://fosdem.org/ [6] https://fosdem.org/2024/practical/conduct/

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L4Re: stack allocation of moderately large arrays
by Paul Boddie 13 Nov '23

13 Nov '23

Hello, Having seen a problem recur in programs running in L4Re just now involving arrays of a relatively large size allocated statically in functions - about 100000 bytes or so - I was wondering if there are any implicit limitations with this form of allocation in L4Re. Is it possible that programs have a limited stack size and that the stack does not expand? Here is an example of the kind of code that causes an unhandled exception: uint32_t Spi_gpio::send_units(uint32_t bytes, const uint8_t data[], uint8_t unit_size, uint8_t char_size) { uint32_t chars = bytes / unit_size; int dc[chars]; And the exception looks like this: Unhandled exception: PC=0x1019ca8 PFA=0xfffd075a LdrFlgs=0x0 The actual cause of the exception is an access to an element in the dc array. When I eventually get back to my own experiments with initiating programs in L4Re - not involved with the problem reported here - I intend to look more closely at program stack allocation and expansion strategies, so I suppose this is an appropriate prelude to such work. Thanks for any guidance that might be offered, as always! Paul

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L4Re: Input via UART fails with Ned involvement
by Paul Boddie 19 Sep '23

19 Sep '23

Hello, I have been trying to get some sensible behaviour from various programs running in L4Re that wish to read from standard input, hopefully using the UART, since standard output is successfully sent across the serial connection. However, it appears that Ned does something rather undesirable with the input stream. If I modify the hello example to use fgets and deploy it without Ned (the hello.cfg example in conf/examples), as long as some kind of serial initialisation has occurred, I can enter characters at the serial console and have the program read them. However, if I deploy the same code using Ned (the hello.cfg example in conf/examples), fgets repeatedly returns NULL. Strangely, if I follow the instructions in the L4Re documentation... https://l4re.org/doc/l4re_servers_ned.html#l4re_ned_interactive The ned-prompt program itself just prints "Cmd>" over and over again, failing to read anything. It is as if non-blocking I/O has been enabled, although ned- prompt appears to use readline, so I imagine that there is likely to be a somewhat different explanation. Attempting to enforce non-blocking input using fcntl in the hello example also does not help. Has anyone any suggestions as to why these things do not work? I have tried this on physical hardware as well as in QEMU. Thanks in advance, Paul

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L4Re uvmm guest OS
by Radu Aron 22 Aug '23

22 Aug '23

Hi, Is it possible to have a Windows guest OS running on top of L4Re? If so, could you provide some insight into how that could work? It seems like uvmm doesn't allow booting from an ISO image, or am I missing something?

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ARM TrustZone with UVMM
by Michael Willig 11 Jun '23

11 Jun '23

Hi all, I would like to try Fiasco/L4Re for a Mixed-Critical Xilinx UltraScale+ FPGA-MPSoC (the hardware accelerators on the FPGA should be virtualized/isolated for mixed-critical applications) Is there somewhere an example (or at least starting point) of an ARM Trustzone configuration of a Normal World VM and Secure World VM (with UVMM/Fiasco as hypervisor that also takes care of the ARM Trustzone configuration)? Best regards Micha

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L4Re: Allocating pinned memory and obtaining its physical address
by Paul Boddie 24 May '23

24 May '23

Hello, Sorry to be lazy and not dig too deeply into the documentation and code, but once upon a time it was possible to use the l4re_ma functions to allocate pinned memory. Then, one would use the dataspace protocol to obtain the physical address of the memory via the capability involved in memory allocation. This exercise would be sufficient to get into a position to initialise peripherals in a system-on-a-chip, setting registers with the physical memory addresses they would need for things like DMA. The initialisation of things like framebuffers would rely on this procedure. I see that the "phys" operation in the dataspace protocol was discarded some time ago, and now there is a "DMA space" abstraction instead: https://l4re.org/doc/group__api__l4re__c__dma.html Are there any examples of how I might obtain a physical address associated with a block of memory using this new API? Thanks in advance for any guidance that might be offered! Paul

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L4Re: Boot module copying and the MIPS Creator CI20
by Paul Boddie 21 May '23

21 May '23

Hello, As part of reviewing my earlier efforts getting L4Re running on various MIPS- based devices, I have been trying to get the bootstrap module to start the kernel on the MIPS Creator CI20, and here I encounter a strange problem. The bootstrap code appears to copy the different modules in the payload around in memory, and for the kernel, it finds the different sections at 0x2f4000 in physical memory (accessed via 0x802f4000), copying them into locations relative to the indicated module base address (for example, 0x1100000 or 0x2000000). From their new locations, each section of the kernel is then copied to its desired final address. So, the section of the kernel providing its entry point can be found at 0x2f4000 + 0xa411c, this being copied to base + 0xa411c, before finally being copied to 0x800d3000. However, the contents of memory at the final location (0x800d3000) are not correct, nor are they at the "staging" location of base + 0xa411c, even though they do correspond to the expected contents of the kernel binary at their original location. What I expect to see at the entry point is... 40806000 mtc0 zero,c0_status 000000c0 ehb What I see instead is... ffffffff bea3ffdf Apart from at the original location in the payload (0x2f4000 + 0xa411c). As far as I can tell, the second word is nonsense, and it is usually followed by more ffffffff words. So, it is as if copying failed for this particular section. Oddly, this only seems to affect the section of the kernel providing the entry point, and all other sections appear to be copied correctly from their original locations. One factor might be that this section is the last one that is copied. Does this seem like recognisable behaviour of some kind of misconfiguration? For the most part, I am just rebasing my old patches on the current L4Re and Fiasco versions, so I didn't expect a problem at this level. Regards, Paul

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building x86-32
by Lieutenant_Beaver＠web.de 11 Mar '23

11 Mar '23

3 3

GI Operating-Systems + Fault Tolerance Meeting
by Horst Schirmeier 26 Jan '23

26 Jan '23

Hello microkernel hackers from Dresden and afar, the German Society of Informatics (GI) has a Special Interest Group on Operating Systems ("Fachgruppe Betriebssysteme" [1]), with members from both academia and industry. This group meets twice a year to network and to discuss their current work. The upcoming spring meeting, organized together with GI's fault-tolerance SIG ("Fachgruppe Fehlertolerierende Rechensysteme" [2]) will be hosted by TU Dresden on March 06+07 (noon to noon). Please consider attending and/or submitting a talk (details below and on the following website): https://www.betriebssysteme.org/aktivitaeten/treffen/2023-dresden/ Best regards, Horst Schirmeier [1] https://betriebssysteme.org [2] https://fg-fers.gi.de/ === Topic: "Operating Systems and Dependable Systems" === Dependability – the totality of safety, security, availability, reliability, and maintainability – is a fundamental attribute of safety-critical hardware and software systems. In the automotive industry, for example, current trends in autonomous driving present entirely new challenges in marrying fault tolerance and maximum performance while keeping costs low. The answers to these research questions ultimately call for a comprehensive investigation of the interactions between applications, system software, and hardware. In this spirit, the joint spring meeting of the GI's "Operating Systems" (FGBS) and "Fault-Tolerant Computing Systems" (FERS) special interest groups will be focusing on novel approaches to the analysis, design, and evaluation of dependable systems and on the exchange of ideas between the two communities. Areas of interest for submissions include, but are not limited to: - Fault tolerance mechanisms at all layers of the system - Dependability and real-time - Isolation and integration mechanisms in software - Test, analysis, evaluation, and verification - Robust system architectures and HW/SW co-design - Practical and field reports on safety-critical systems and their applications - Models, development processes, and standards Contributions outside the main focus of the event are most welcome as well. Please submit either a one-page abstract (presentation only) or a 2- to 4-page unpublished paper (ACM conference style) in German or English. A program committee consisting of members of the two steering boards will review the submissions and decide on their acceptance. In case of acceptance, papers (2-4 pages) will be published in the digital library of the Gesellschaft für Informatik. We explicitly welcome presentations in English. The talks' language will be indicated in the program to facilitate non-German members' participation in our workshops in the future. The event will also be organized in a hybrid format. -- Prof. Dr.-Ing. Horst Schirmeier Professur für Betriebssysteme Technische Universität Dresden Fakultät Informatik 01062 Dresden Tel.: +49 (351) 463-38321 office: Andreas-Pfitzmann-Bau, R.3102 Nöthnitzer Str. 46, 01187 Dresden (Campus-Navigator: https://tud.link/seh0) https://tud.de/inf/os

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L4Re: uClibc and UTCB/TCR initialisation
by Paul Boddie 01 Oct '22

01 Oct '22

Hello, I have been working through reimplementing the mechanisms involved with launching programs in L4Re, managing to initiate programs apparently successfully under QEMU emulating amd64 and x86, but I have been less successful getting them to work under QEMU emulating a MIPS system (MIPS Malta). My arrangement of threads within tasks should be fairly similar to what L4Re normally employs to host and run programs, and I wrote it up here: "Gradual Explorations of Filesystems, Paging and L4Re" https://blogs.fsfe.org/pboddie/?p=2540 The pictures at the end summarise what has been done. I have a region mapper running in a thread in the same task as the program to be launched. The region mapper handles page faults and interacts with dataspaces on the program's behalf. Faults caused by the region mapper are handled by the initiating task. What I seem to have avoided previously but now experience is that after the region mapper has been started, it is able to service page faults, but after a certain point in the execution of the program of interest, the region mapper itself experiences an exception in the __pthread_cleanup_push_defer function within uClib's pthreads implementation, specifically at this line: buffer->__canceltype = THREAD_GETMEM(self, p_canceltype); Digging into this, I found that self is apparently zero. Since self is obtained from a call to thread_self which in turn obtains the user[0] member of the thread control register structure (providing the thread descriptor address), I can only conclude that either this member has not been initialised or that it has been overwritten by the other thread as it started up. Investigating uClibc startup, I notice that pthread initialisation does indeed involve a traversal of UTCB areas, zeroing user[0] in the supposedly free UTCB blocks. And with the region mapper having failed, the main program will also fail fairly quickly, with an exception typically occurring in the __pthread_initialize_minimal function, coincidentally just after this zeroing has occurred, just before a call to __libc_setup_tls. I have been looking for hints as to how this work is done in L4Re normally. Given that the region mapper and the program being run are normal programs that are executed via their conventional entry points, this resulting in the initialisation of the C library and threading for each payload, it seems that some measures must be in place to prevent this initialisation from causing conflicts in the UTCB area. For instance, I see that in the file... pkg/l4re-core/l4re_kernel/server/src/main.cc ... the __libc_alloc_initial_tls function is redefined to presumably override the weakly referenced version in uClibc, but if this were invoked it would probably cause uClibc to fail during initialisation, at least unless the zero page is going to be used (but it would need allocation somewhere else), so maybe it doesn't override anything after all. In any case, this function would only change some aspects of how __libc_setup_tls would work, so maybe it is a distraction. I did wonder if there was something specific about MIPS that would cause this failure, investigating the user-local register (ULR) used to hold UTCB-related information, but getting the UTCB address via the ULR would appear to work: otherwise, the region mapper would probably not start up. I also wondered about program initialisation issues, since I did experience problems on actual MIPS hardware related to various registers not being set up correctly, but the generated code seems fairly comprehensive in this regard these days (and maybe it was all along but I encountered a confounding phenomenon). Does anyone have any familiarity with how this actually works and might be able to indicate what I am doing wrong? As always, thanks for any help that can be offered! Paul

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