Tuesday, December 10, 2013

Effective Terminal Windows

This one's for all the terminal junkies out there.

I have a tendency to open about 10-20 terminal windows at a time, and it gets hard to track which terminal is in use for which ongoing project. The defaults for my distro are to put a ridiculously long and useless title on the terminal, and the prompt shows the entire working directory. Titles get really long when the directory structure is nested more than 8 or so levels. I did a little searching and found the right set of configuration commands for bash to make my terminal titles and prompts more useful for me. Now my title shows the current working directory name, and the prompt shows at most 6 levels (the current directory and its 5 ancestors).

Add the following after the definition of PS1 in .bashrc to get my configuration:

# If this is an xterm set the title to the current directory name
case "$TERM" in

# cut off really deep prompts

Thursday, October 3, 2013

Software product country of origin (COO)

Late last year, US Customs (CBP) issued an advisory ruling regarding how to determine the COO for software products when software is developed partially in a country not listed in the Trade Agreements Act as a designated country. For example, China is not a designated country. A fair description has been written up here. The ruling provides a template for labeling the COO as a designated country despite using source code developed in a non-designated country.

The reason software companies would want to certify their product's COO as a designated country is so they could sell their software to the US Government. The main problem is that competitors (or whistleblowers) can sue under the False Claims Act. Significant damages can be awarded if the court finds the COO is not correct.

Now the companies that want to label their software COO as a designated country can get a better chance at either defending such claims or getting a binding ruling from CBP. These companies are scrambling to hire law firms to determine if the advisory ruling can help, to seek a binding ruling from CBP, and to otherwise gather evidence to use to back COO claims. I consulted for BlankRome LLP to help them with just such a task. In particular, I examined their client's software development processes to help determine whether and how they fit the template, and to see what evidence there is to claim that the software product is "Made in the USA" despite the fact that much of the software, in terms of source code, has been written in China. While the details of my engagement (who, what, how) are covered by an NDA, I can give some high-level intuition on the issue.

At first blush, it seems counter-intuitive that the bulk of software can be written in one country, while the end product claims to be another. The defensible stance, however, is to claim that the creativity and human knowledge required to make the software comes out of the design, requirements specifications, and testing/validation. The key seems to be that experts in the US should be involved in making decisions both about how the software is written and in selecting the code modules to use.

Thursday, May 30, 2013

Congratulations RTEMS GSoC 2013 Students

Congratulations to the accepted students in GSoC 2013 for the RTEMS Project! We had many fine applicants again this year, and were able to accept 9 students to do projects with us this summer. In alphabetical order by project name, we accepted these students/projects:
  • Shubham Somani
    • Application Configuration GUI for RTEMS.
  • Deng Hengyi
    • Atomic Operations and SMP lock debug tool for RTEMS
  • Dhananjay M Balan
    • Better debugging support for RTEMS in GDB.
  • Hesham Moustafa AL-matary
    • Enhance low-level API of libmm (Memory Protection & Caches)
  • Philipp E
    • Paravirtualization layer in RTEMS
  • Jin Yang
    • Porting CAN driver, LinCAN, to RTEMS
  • Peng Fan
    • RTEMS Runtime Loader
  • Sree Harsha Konduri
    • SMP Aware Scheduler
  • Vipul Nayyar
    • Unified APIs
These are all important, ambitious projects that will be of great benefit to RTEMS if successful, and will definitely teach the students a lot about project management and open source development.

Thursday, May 9, 2013

Who's calling me? Visualizing function callers

My problem today was to determine and visualize the set of functions (callers) that call another set of functions (callees). For this purpose, I knew the callees function names all started with the same word, say "Callee", and that none of the caller's names start with Callee. For C programs, namespaces are often formed by a coding convention that specifies the format of function names and groups related functions by a common "first name".

I found a simple tool, egypt, that relies on gcc and GraphViz to generate a visualization of a program's static call graph. A call graph is a natural way to visualize what I need, but my requirements are slightly different than the usual. Normally a call graph will include all of the directed edges from callers to callees in an entire program or subset of its functions. What I need is just the nodes of immediate callers of the Callee functions, that is, the subgraph induced by the caller and callee vertices in the call graph.

For my needs, the tool lacks the ability to specify a set of vertices and generate the subgraph they induce. The induced subgraph could be found if I could:
  • specify terminal nodes (callees)
  • filter nodes that do not have an edge to terminal nodes
Rather than implement this ability, I realized I could wrap egypt with a bit of shell code to produce the graph(s) I want.

egypt processes RTL dumps produced by gcc. It outputs a call graph for the RTL dump files passed in. The first thing to do then is to compile the project to visualize using gcc with the -fdump-rtl-expand flag. This produces the *.expand files required by egypt. My first attempt was using gcc 4.4.7, which dumps all of the .expand files in the root directory of the build. For projects with multiple source files having the same name, the .expand files overwrite each other. I switched to gcc 4.7.1 because it dumps the .expand files in the same directory as the .o files are generated. Then, I revisited some old tricks to gather the .expand files into a separate directory for analysis while keeping the project's directory structure.

Now, if I just wanted the callgraph of the Callees, I could easily grep for the .expand files containing functions that start with Callee and pass them to egypt. However, to get the subgraph of caller->Callee is trickier. What I did was to use egypt on each of the .expand files individually and filter the output for edges to a Callee. This gives exactly the set of nodes and edges I need. Then I just need to wrap the output similarly to how egypt does to produce a graph file for GraphViz. The resulting script looks something like,
echo "digraph callgraph {"
files=`find . -name "*.expand"`
for f in $files
  egypt --include-external $f | grep Callee_ \
        | grep -v Callee_.*-\> | grep -v Callee_.*\"\;
echo "}"
The --include-external is necessary to force egypt to produce caller nodes for which it does not find a definition. The second line of greps are to exclude any calls originating from Callee, and to discard any uncalled Callee. Redirect the output of the script to a file, say callgraph.dot, and then it can be processed with one of the layout engines in the dot tools, like
$> dot -Teps -o callgraph-neato.eps callgraph.dot

As an example, I processed the RTEMS Supercore Scheduler package. For this package, the Callee is _Scheduler. I processed the output with the circo drawing filter.
Supercore Scheduler Callers, with Scheduling Functions filled in Grey

Some further improvements could be made. It might also be interesting to visualize the paths (open walks) that end at the Callees. Also, the egypt tool works only on the static call graph, so indirect function calls e.g. through function pointers are not captured. Making use of dynamic profiling tools that generate a call graph, such as gprof or callgrind, could improve the accuracy of the visualization.

Tuesday, May 7, 2013

Software Licenses with RTEMS

The RTEMS license is a modified version of the GPL version 2 that includes an exception to permit including headers and linking against RTEMS object files statically. Normally, the GPL can only be linked statically with other GPL code, or rather, linking statically with GPL code would cause your code to become GPL code. The LGPL is not a suitable alternative, because it either requires use of a shared library that can be re-linked, or release of the linked (application) code. And newer versions (GPL version 3) are completely unsuitable for embedded systems due to the relinking restriction which is technically challenging.

A problem for RTEMS is there are no copyleft licenses that are compatible with the RTEMS license. Thus, RTEMS Project has to reject any code that uses the GPL or LGPL, even though RTEMS seems to use the GPL itself---this is because of the exception for static linking, and also because an upstream GPL version 2 project could at any time switch to GPL version 3 and become totally unusable. In practice, RTEMS can only accept original code contributed under the RTEMS License and code that has a permissive license.

I could not find any license that provides the copyleft protection of a software project while still allowing static linking of proprietary software. Maybe there is some subtle legal or technical issue that I do not understand, but it seems like such a license ought to exist somewhere that protects the free software while permitting applications to use it; a sort-of "Embedded GPL".

Some things that RTEMS could do better include:
  • Collect all of the copyright and license disclaimers for users
  • Collect all of the advertising restrictions, or move those encumbered files to a secondary repository
  • Switch from the GPL + linking exception, but to what I do not know
Update 5/8/13: Identified that RTEMS uses version 2 of the GPL, and give some background on why RTEMS has not and will never switch to version 3.

Friday, April 19, 2013

Generating interrupts with a gem5 device

Today I extended my work of adding a device to gem5 by causing the device to generate an interrupt. Interrupts seem to be architecture-specific in gem5, so I needed to include some X86-specific functionality. I copied the approach taken in gem5 for the x86 keyboard interrupts, but with IRQ 3 (because it was available) for my device.

The following files should help recreate this effort:
  • device.diff - apply to gem5 to create simple device.
  • interrupt.diff -  apply to gem5 with device.diff to add interrupt.
  • mydev.c - device driver Linux kernel module.

Thursday, February 28, 2013

Adding a simple io device to gem5

Last time, I added custom pseudo-instructions in gem5. Today, I add a device in gem5 and then use the device from within a simulated (linux-x86_64) system.

Adding a device to gem5 is lightly documented in the ASPLOS tutorial and gem5 wiki. I would suggest starting with the tutorial, and read about the memory system as well.

Devices are located in gem5/src/dev/ subtree, with architecture-specific files located in subdirectories. The IsaFake device, which I found before the ASPLOS tutorial, was useful for starting. To create a simple device, I copied isa_fake.[cc|hh] to mydev.[cc|hh], and copied BadDevice.py to MyDevice.py. Then I copied the parameters for IsaFake from Device.py into the parameters of MyDevice.py, and added mydev.cc and MyDevice.py to the SConscript. After renaming (search-replace IsaFake/BadDevice with MyDevice, isa_fake with mydev, etc), I needed to add the device to the system. I'm working with x86, so I attached it in the x86/Pc.py file, with:

from MyDevice import MyDevice
    my_device = MyDevice(pio_addr=x86IOAddress(0xe000), pio_size=8)
        self.fake_floppy.pio = bus.master
        self.my_device.pio = bus.master
        self.pciconfig.pio = bus.default

After compiling and running gem5 the device is listed in the m5out/config.ini file.

Accessing the device requires a device driver. To learn about writing drivers, read a good book. For this driver, a simple kernel module will do.
#include <linux kernel.h>
#include <linux module.h>
#include <linux errno.h>
#include <linux ioport.h>
#include <asm io.h>

#define BASE 0xe000
#define SIZE 0x08

int init_module(void)
  int t1;
  if ( ! request_region(BASE, SIZE, "mydev") ) {
    printk( KERN_INFO "unable to get io port at 0x%8X\n", BASE );
    return -ENODEV;

  /* a little test */
  t1 = inl(BASE);
  printk( KERN_INFO "read %d\n", t1 );

  outl(0, BASE);
  t1 = inl(BASE);
  printk( KERN_INFO "read %d\n", t1 );
  return 0;

void cleanup_module(void)
  release_region(BASE, SIZE);

Compile the module against the Linux kernel, boot gem5, get the module into the simulated system (e.g. with m5 readfile), and insert the module. With the default parameters from the IsaFake device, the write is ignored and the device returns -1 whenever it is read.

I did not get I/O memory working, but for now I/O ports are fine for me.

Tuesday, February 12, 2013

Add a pseudo instruction to gem5

An important aspect of many computer architecture projects is to modify an instruction set, often to extend the instructions with a new instruction that implements a proposed feature. I'm working on moving some of my research to the GEM5 open source simulator, but first I need to get an idea of the level of effort involved. My first move is to figure out how to add new instructions.

GEM5, being designed especially for computer architecture research, has a well-defined set of pseudo instructions that can be extended to serve my purposes. However, there are not really any instructions on how to extend these instructions. The few emails that I could find about pseudo instructions basically just said go look at what is implemented and extend it. So that is what I did. For posterity, I'll relay my findings here. Maybe they will be helpful to others, or to myself in the future.

The pseudo instructions are useful for implementing functional simulator features that can use a multiple-register instruction. The main drawback is that the pseudo instructions are not integrated tightly with the pipeline and are executed non-speculatively, so if the rate of your new instruction is quite high, the cost could be misleading if doing performance evaluations of the new feature. For my work, the pseudo instruction is fine; I have previously done a very similar implementation for functional simulation with Simics/GEMS.

Adding a new pseudo instruction (for X86)

I'm interested primarily in the X86 full-system simulation capabilities of GEM5 at the moment, so my effort is in that area. However, the pseudo instructions have implementations in the other architectures, and most of the following will translate directly to them.
  • Overwrite a reserved opcode in src/arch/x86/isa/decoder/two_byte_opcodes.isa near the other pseudo instructions (look for m5panic).
  • Add the instruction’s functional simulation implementation in src/sim/pseudo_inst.cc
  • Add the function prototype in src/sim/pseudo_inst.hh. The function prototype will define the available registers for parameters and return values based on the compiler’s calling conventions for the architecture.
  • Create an m5op for easily emitting the instruction in compiled code.
    • Add function number in util/m5/m5ops.h
    • Add function prototype in util/m5/m5op.h
    • Instantiate a TWO_BYTE_OP in m5op_x86.S
I have written a simple example that implements addition as a pseudo instruction. The patch may bit-rot, but the idea should be easy enough to follow.

To use the new pseudo instruction call the function declared in util/m5/m5op.h. Then (cross-)compile your source code with the m5 utilities like:
  gcc -o foo foo.c -I ${GEM5}/util/m5 ${GEM5}/util/m5/m5op_x86.S

To get your code into the simulation, you can
  • add the binary to the disk image 
    • sudo mount -o loop,offset=32256 /dist/m5/system/disks/linux-x86.img /mnt/tmp
    • cp foo /mnt/tmp/bin
  •  or read it directly into the simulation 
    • build/X86/gem5.debug configs/example/fs.py -r 1 --script=foo
    • m5term localhost 3456
    • m5 readfile > foo
    • chmod +x foo
    • ./foo
Adding to the disk image requires restarting the simulation, whereas if you have a checkpoint loaded you can read the file in directly using m5 readfile.

Executing the pseudo instruction on real hardware

You can also use your new pseudo-instruction in real hardware by providing an illegal instruction handler (SIGILL handler) that emulates the functionality of the instruction. This may be useful for debugging purposes, since native hardware can run the emulation code much faster than the simulator will. I have written a simple example that shows how to handle the illegal instruction signal that gets caused when the pseudo instruction is executed. This sample example will execute in both GEM5 and natively (on a 64-bit X86).

I guess that covers it for now. Happy hacking!

Monday, February 11, 2013


I previously wrote about booting RTEMS on M5 (Now gem5) SPARC_FS. I am following up on this work in preparation for the release of RTEMS 4.11, which will hopefully be coming soon. I compiled RTEMS (with two small patches) and booted two samples on gem5 and on Simics Niagara.

On the simulator side, the instructions I gave previously continue to work for booting both OpenSolaris and RTEMS. I updated some of the links in the prior post to reflect the change in host to Oracle for the OpenSPARC tools. One issue I did not notice at first is that the port for the console to connect m5term to the gem5 simulator is port 3457.

I successfully built and booted hello and ticker with the niagara BSP. There are a few patches that need to be applied to RTEMS, but hopefully I can get those patches committed before releasing 4.11. Ideally, the RTEMS 4.11 will be able to compile and boot with gem5, giving the RTEMS community an open-source simulator for testing.

Interestingly, the ticker appears to count time. I'll have to take a look at how gem5 simulates the (s)tick register. Simics does not simulate the timer with any accuracy.

I think Qemu would be a nice target simulator for some future endeavors, but I do not have the time to investigate the feasibility of running RTEMS on the Qemu Sparc64.

Thursday, February 7, 2013


I finally learned how to use screen, a terminal windowing program that can detach so its windows run as a background task. When you detach, screen returns you to your shell. Detaching allows me to start work on a server from my lab workstation in a screen session, detach screen, logout and turn off my workstation, go home, and resume the same screen session from home.

Start screen with
$> screen
Once inside screen, the windows act mostly like a terminal, but now you can issue commands to screen using Ctrl-a and a command key. The useful keys that I have been using are:
  • Create a window (Ctrl-a c)
  • Next (Ctrl-a n) or Previous (Ctrl-a p) window.
  • Detach (Ctrl-a d)
To start screen with a previously detached session, first find the session with:
$> screen -ls 
There are screens on:
    11999.pts-0.localhost    (Attached)
    17129.pts-3.localhost    (Detached)
$> screen -r 17129.pts-3.localhost
The -r flag resumes the detached screen session.

Detaching is useful especially for long-running programs or for conserving the state of many terminal windows.

Thursday, January 24, 2013

Profiling C++ applications: class composition

In the latter half of last year, my research went down an OOP path especially in the direction of C++; both the hardware containers project and my thesis touch elements of OOP concepts. With the hardware containers we were interested in how C++ developers use inheritance, composition, and encapsulation. For my thesis work, I was interested in how applications use the STL; I wrote an appendix in my thesis describing this aspect. For this post, my focus is on the hardware containers work, which is in my paper pipeline waiting for submission.

I found 21 free and commercial (oxymoron?) open-source C++ programs for this investigation: dimacs-sq, Dijkstra's algorithm; Opal and GEM5, processor simulators; Geant4, physics particle simulator; FlightGear, flight simulator; Wesnoth, video game; OpenCV, computer vision library; Boost, library for C++; MySQL, database server; LibreOffice, office productivity suite; Doxygen, documentation generation; Haiku, OS based on BeOS; ReactOS, OS based on Windows NT; Chromium, web browser; povray, soplex, dealII, namd, xalancbmk, astar, and omnetpp, C++ benchmarks from SPEC CPU 2006.

Using synthetic microbenchmarks, Eugen and I determined that the important C++ code behavior attributes that affect performance when using hardware containers are the ratio of private access specifiers to total number of class variables, depth of inheritance, number of objects a class includes by value, and number of public accessor methods that expose private variables. Nicely enough, all of these can be determined by examining source code: no need to run the C++ programs!

I used two tools to analyze the 21 programs: Understand by SciTools, and CCCC. The former is commercial and comes with an evaluation license, which was enough for me to get the data I wanted; the latter is open-source, which was good enough for me to modify to get data I wanted. I used Understand! to measure the ratio of private:class variables and the depth of inheritance, but the tool did not provide enough data for the objects included by value or for accessor methods. Ultimately I did not get any data for the latter, but I was able to hack CCCC to measure how many objects a class includes by value.

For the composition of classes I used my modifications to CCCC to count how many classes each class includes by value. On average, classes do not include very many objects of other classes by value (perhaps by reference), although large outliers exist. The chart shows the average number in orange, with one standard deviation as an error bar; the maximum among all the classes is in blue.

I used both CCCC and Understand to calculate the inheritance tree depth of these C++ programs. Using both tools showed some difference in the tool quality, since for a metric as simple as inheritance depth the two tools should get identical numbers. The following chart shows the maximum depth of the inheritance tree reported by each of the two tools with CCCC in blue and Understand in orange.


Although the tools occasionally agreed, vastly different numbers were obtained for lots of the programs. The maximum inheritance depth is less than 10 for almost all of these programs, with small (near 1) averages and standard deviations. Thus most classes are decoupled with small inheritance and composition factors, but some strong outliers do exist. For hardware containers, we can treat the outliers as a special case and make safe (enough) assumptions about an object's composition.

Tuesday, January 22, 2013

My new job

As of last week I have started my new full-time job as a Postdoctoral Research Scientist at GWU. I'm working with my thesis co-adviser, and my job is an expanded version of what I was doing before graduating. In addition to continuing my research, I will also be overseeing/assisting the research of some graduate students and writing grant proposals.

The appointment is for the next 18 months or so, and I'm excited about carrying forward the momentum I have in my research.

Looking back to 2012, forward to 2013

Of the many post ideas back-logged in my head, I wanted to recap the past year and perhaps look forward to the new year before making it out of January. For me, 2012 was a busy year in which I
  • Became a dad.
  • Defended my Ph.D. dissertation.
  • Dropped 20 pounds to 18% body fat, BMI 23.
  • Bicycled 2300 miles, ran another 160 or so.
  • Published 2 papers and a book chapter.
  • Continued RTEMS involvement as an admin and mentor for GSOC and GCI.
  • Went on a Caribbean cruise.
  • Bought my first car, a minivan.
  • Repaired/Improved my house: foundation crack sealed, water line repaired, water line replaced, water heater replaced, roof repairs, HVAC heat pump and blower replaced, ventilation ducts cleaned, and kitchen cabinets refaced.
For 2013 some of my goals, resolutions, and expectations are to
  • Turn 30. Done!
  • Get a job. Done, more on that soon.
  • Publish more.
  • Get more research funding.
  • Read more.
  • Learn a new (non-programming) language, probably ASL or suomi.
  • Continue RTEMS involvement.
  • Resume regular exercise. I cut way back after my daughter was born.
  • Finish a century ride, solo or supported. Current best: 88 miles.
  • Finish a half-marathon, solo or organized. Current best: 8 miles.
  • Take up swimming.
  • Go on a family vacation.
  • Build a "front porch."
  • Construct a new cat tower.
  • Get rid of stuff.
  • Be a better person.