Intel Blog: Why Target Variation Matters (finding a Xen bug)


Simics and other simulation solutions are a great way to add more variation to your software testing. I have just documented a nice case of this on my blog at the Intel Developer Zone (IDZ), where the Simics team found a bug in how Xen deals with MPX instructions when using VT-x.  Thanks to running on Simics, where scenarios not available in current hardware are easy to set up.

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Reverse Debug with Hardware in the Loop

reverse iconLast year (2015), a paper called “Don’t Panic: Reverse Debugging of Kernel Drivers” was presented at the ESEC/FSE (European Software Engineering Conference and the ACM SIGSOFT Symposium on the Foundations of Software Engineering) conference. The paper was written by Pavel Dovgalyuk, Denis Dmitriev, and Vladimir Makarov from the Russian Academy of Sciences. It describes a rather interesting approach to Linux kernel device driver debug, using a deterministic variant of Qemu along with record/replay of hardware interactions.  I think this is the first published instance of using reverse debugging in a simulator together with real hardware.

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First post on the Intel Software and Services Blog

intel sw small I have posted my first blog post to the Intel Software and Services blog channel. The Intel Software and Services blog is one channel in the Intel corporate blog you find at  Other bloggers on the Software and Services channel write about security, UEFI, cloud, graphics, open source software, and other topics. Intel has a large software development community, and we produce quite a bit of software – and we do write about the innovations that come out of Intel that rely on software.

On my part, I will be posting more materials on simulation at Intel, as part of my role as a simulation evangelist on the Software and Service blog channel.


Breaking and Detecting Simulators and Emulators

binary codeI have read a few news items and blog posts recently about how various types of software running on top of virtual machines and emulators have managed to either break the emulators or at least detect their presence and self-destruct. This is a fascinating topic, as it touches on the deep principles of computing: just because a piece of software can be Turing-equivalent to a piece of hardware does not mean that software that goes looking for the differences won’t find any or won’t be able to behave differently on a simulator and on the real thing.

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Busy Writing a Book About Simics

once upon a time - squaredFor the past six months I have not been doing much blogging at all, neither here nor on the Wind River blog.  The reason is that I have been directing my writing energy into writing a text book about Simics together with Daniel Aarno at Intel.  Last year, Daniel and I worked on an Intel Technology Journal issue on Simics.  The ITJ issue was kind of a first step on the way to the book, collecting several articles about Simics usage at Intel and elsewhere.  The book itself will be much more of a detailed description of Simics and how it works and why it works the way it works.

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Intel Technology Journal on Simics

Simics_ITJ_180-wideThe September 2013 issue of the Intel Technology Journal (which actually arrived in December) is all about Simics. Daniel Aarno of Intel and I served as the content architects for the issue, which meant that we managed to contributed articles from various sources, and wrote an introductory article about Simics and its usage in general. It has taken a while to get this journal issue out, and now that it is done it feels just great! I am very happy about the quality of all the ten contributed articles, and reading the final versions of them actually taught me some new things you could do with Simics! I already wrote about the issue in a Wind River blog post, so in this my personal blog I want to be a little bit more, well, personal.

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S4D Paper on Transporting Bugs with Checkpoints

I have a paper about “Transporting Bugs with Checkpoints” to be presented at the S4D (System, Software, SoC and Silicon Debug) conference in Southampton, UK, on September 15 and 16, 2010. The core concept presented is to leverage Simics checkpointing to capture and move a bug from the bug reporter to the responsible developer. It is a fairly simple idea, but getting it to work efficiently does require that some things are done right. See the longer Wind River blog posting about this topic for a few more details.

Wind River Blog: Interview with a Virtualization Researcher

Past Friday, I posted a new blog post in my Wind River blog. It is an interview the PhD student Girish Venkatasubramanian from the University of Florida. He is doing research on virtual machines/hypervisors and how they can be implemented more efficiently by making fairly small changes to the architecture of memory management units.

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FLOSS Weekly on Xen: Some Background Missing

flossweeklyFLOSS Weekly recently ran an interview with the creator of the Xen project, Ian Pratt from the University of Cambridge (and now working for Citrix since they bought Xensource). Since I happen to like virtual things, even the so-much-talked-about-it-hurts IT/server/desktop virtualization world this was a must-listen. It was a good show, but lacking some in the humble background department.

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Cadence on Virtual Prototypes instead of Host Execution

Cadence technical blogger Jason Andrews wrote a short piece a couple of days ago on his perception that host-based execution is becoming unncessary thanks to fast virtual platforms. In “Is Host-Code Execution History“, he tells the story of a technique from long time ago where a target program was executed directly on the host, and memory accesses captured and passed to a Verilog simulator. The problem being solved was the lack of a simulator for the MIPS processor in use, and the solution was pretty fast and easy to use. Quite interesting, and well worth a read.

However, like all host-compiled execution (which I also like to call API-level simulation) it suffered from some problems, and virtual platforms today might offer the speed of host-compiled simulation without all the problems.

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What is Efficiency when Cores are Free?

More from the SiCS multicore days 2008.

There were some interesting comments on how to define efficiency in a world of plentiful cores. The theme from my previous blog post called “Real-Time Control when Cores Become Free” came up several times during the talks, panels, and discussions. It seems that this year, everybody agreed that we are heading to 100s or 1000s of “self-respecting” cores on a single chip, and that with that kind of core count, it is not too important to keep them all busy at all times at any cost. As I stated earlier, cores and instructions are now free, while other aspects are limiting, turning the classic optimization imperatives of computing on its head. Operating systems will become more about space-sharing than time-sharing, and it might make sense to dedicate processing cores to the sole job of impersonating peripheral units or doing polling work. Operating systems can also be simplified when the job of time-sharing is taken away, even if communications and resource management might well bring in some new interesting issues.

So, what is efficiency in this kind of environment?

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Google Chrome and Parallel Browsing

Everybody seems to think the launch of the Google Chrome browser is very important and cool. Probably because Google itself is considered important and cool. I am a bit more skeptical about the whole Google thing, they seem to building themselves into a pretty dangerous monopoly company… but there are some interesting architectural and parallel computing aspects to Chrome — and Internet Explorer 8, it turns out.

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Virtual Platforms for Late Hardware and the Winds of History

As might be evident from this blog, I do have a certain interest in history and the history of computing in particular. One aspect where computing and history collide in a not-so-nice way today is in the archiving of digital data for the long term. I just read an article at Forskning och Framsteg where they discuss some of the issues that use of digital computer systems and digital non-physical documents have on the long-term archival of our intellectual world of today. Basically, digital archives tend to rot in a variety of ways. I think virtual platform technology could play a role in preserving our digital heritage for the future.

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Freescale QorIQ P4080 is out — with Simics support

Only half an hour ago, the embargoes lifted. Freescale announced its new QorIQ series of multicore (and some single- and dual-core) processors. For the top-end of that line, the P4080, Freescale and Virtutech (where I work, remember) have developed a virtual platform solution to help Freescale customers get to working products faster. The virtual platform is available now, and is already running several operating systems including VxWorks, QNX, and a variety of Linuxes. Apart from the fairly large scale of this SoC, the really new part of the virtual platform is the so-called Hybrid solution, where the fast models are combined with detailed models from Freescale themselves. This creates a cycle-level detailed model with validated timing, “from the source” — but without the performance issues of having to run everything at great level of detail. Rather, you use the fast model to steer the simulation of a workload to an interesting spot, and then turn up the level of detail then and there. You can also select which components of the chip are actually detailed and which parts are modeled with the fast functional models, avoiding the incredible slow-down of running and entire virtual platform at a great level of detail.

If you happen to be at the FTF in Orlando, do come by and look at the demos!

I have been involved in this work for the past year, and it is wonderful to finally see it coming out and be able to talk about it.

The 1970 rule strikes again: Virtual Platform Principles in 1967

Being a bit of a computer history buff, I am often struck by how most key concepts and ideas in computer science and computer architecture were all invented in some form or the other before 1970. And commonly by IBM. This goes for caches, virtual memory, pipelining, out-of-order execution, virtual machines, operating systems, multitasking, byte-code machines, etc. Even so, I have found a quite extraordinary example of this that actually surprised me in its range of modern techniques employed. This is a follow-up to a previous post, after having actually digested the paper I talked about earlier.

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Virtual Platform by Virtualization Extensions — 1969

By means of a trip down virtualization history, I found a real gem in 1969 paper called A program simulator by partial interpretation, by Kazuhiro Fuchi, Hozumi Tanaka, Yuriko Manago, Toshitsugu Yuba of the Japanese Government Electrotechnical Laboratory. It was published at the second symposium on Operating systems principles (SOSP) in 1969. It describes a system where regular target instructions are directly interpreted, and any privileged instructions are trapped and simulated. Very similar to how VmWare does it for x86, or any other modern virtualization solution.

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VMM Detection Myths and Realities from a Simics and Embedded Perspective

It must have been Google Alerts that send me a link to the HOTOS 2007 (Hot Topics in Operating Systems) paper by Tal Garfinkel, Keith Adams, Andrew Warfield, and Jason Franklin called Compatibility is not Transparency: VMM Detection Myths and Realities. This paper is slightly less than a year old today, so it is old by blog standards and quite recent by research paper standards. It deals with the interesting problem of whether a virtual machine can be made undetectable by software running on it — and software that is trying to detect it. Their conclusion is that it is not feasible, and I agree with that. The reason WHY that is the case can use some more discussion, though… and here is my take on that issue from a Simics/embedded systems virtualization perspective.

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AMP vs Virtualization

It just dawned on me recently (and it sure must have been obvious to those working with configuring AMP — Assymtric Multiprocessing Systems) that in an AMP setup, the operating systems involved actually know about each other and have to account for the fact that they are sharing a single processor chip with other operating systems. So you cannot just take two single-core operating system images from an existing multiple-processor (local memory) solution and put them on a single chip and things just work. You do need to prepare the boot process and find a way to nicely share the common I/O devices, timers, accelerator engines and other resources on the chip. This is materially different from a virtualized setup.

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Fastscale minimal virtual machines — beautiful simple idea

A company called Fastscale Technologies has a product that is simple in concept and yet very powerful. Instead of using complete installs of heavy operating systems like Linux or Windows to run applications on virtual machines, they offer tools that provide minimal operating system configurations that are tailored to the needs of a particular application. Since only that application is going to be run on the virtual machine, this is sufficient. According to press reports, this means that you can run several times more virtual machines on a given host, compared to default OS installs. And boot an order of a magnitude faster.

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Real-Time in Sweden (RTiS) 2007

RTiS 2007 just took place in Västerås, Sweden. It is a biannual event where Swedish real-time research (and that really means embedded in general these days) presents new results and summarizes results from the past two years. For someone who has worked in the field for ten years, it really feels like a gathering of friends and old acquaintances. And always some fresh new faces. Due to a scheduling conflict, I was only able to make it to day one of two.

I presented a short summary of a paper I and a colleague at Virtutech wrote last year together with Ericsson and TietoEnator, on the Simics-based simulator for the Ericsson CPP system (see the publications page for 2006 and soon for 2007). I also presented the Simics tool and demoed it in the demo session. Overall, nice to be talking to the mixed academic-industrial audience.

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