There’s an updated version of the Stray Event Scanner tool available from the download page. Release notes can also be found there; mostly they’re to do with improvements to the command-line version of the tool.
Archive for August, 2008
As I mentioned, about a week ago I visited a customer site to find out if our Stray Event Scanner tool actually did the trick, on their codebase. That customer has kindly said I can post some results here.
Results were mixed!
|Proportion of this customer’s codebase scanned||5% (estimate).|
|False positives reported by the tool||47|
|Of which||are things I might be able to fix||37|
|are intrinsic limitations||8|
|are already fixed in a later development version of the tool||2|
|Interestingly, 35 of these false-positives were in one smallish area of code. It seems that some Symbian OS code conforms to the norms expected by the tool, whilst some code really gets is unnecessarily overexcited. All the rest of the code we scanned only produced 12 false-positives.|
|Real bugs found by the tool||14|
|Of which||tool was precise about the problem||6|
|tool was wrong, or vague, about the specific problem but did identify the right bit of faulty code||8|
|Actual bugs filed in this customer’s defect-tracking system||10 (because the other four were duplicates)|
Conclusions. Good things first…
- As expected, the tool found plenty of bugs. Nearly all of these bugs were real problems which could cause E32USER-CBase 46 panics under some circumstances, which are awful to diagnose.
- In fact one of them was a duplicate of an existing E32USER-CBase 46 bug, which they’d been searching for for some time, but had been unable to find. Result!
- The tool broadly worked as planned. There were no hopeless incompatibilities with their source code.
- With the exception of that one component, there were far fewer false-positives than I realised.
- There were lots of false-positives in that one component. Many of these will be impossible to remove using the current analysis method.
- In some cases the tool was not very accurate about specifying exactly what was wrong with the code. It would identify the right area of code, but a lot of examination and thought was required to identify whether there really was a problem there. Again, there’s not much that can be done about this: stray event problems are intrinsically complicated and somebody technically experienced will be required to analyse the results.
- See how many of those false-positives I can remove easily
- Fix a few other minor bugs that cropped up
- Decide whether the tool is ready to leave the beta stage!
One of the things which would make Macrobug’s life much easier is if Symbian OS had DTrace or an equivalent. DTrace is a dynamic tracing framework which allows arbitrary APIs and function calls to be instrumented at run-time without any changes to any code. That way, the Macrobug tools would be able to hook in and monitor what’s happening inside the device without any changes to the kernel or application binaries.
Such days are probably some way away, but I can look forward to it!
Meanwhile, just as an example of how great DTrace is on a real system, I’ve just used it to diagnose a problem with my Mac. Macs include a backup mechanism known as Time Machine. This does incremental backups, in my case onto a RAIDed NAS server sitting elsewhere in my house (which in turn has parts of it rsync’ed to an off-site backup regularly).
Time Machine backs up automatically every hour in the background, and keeps as many incremental backups as it can fit onto the backup disk. There’s therefore an incentive for the backups to be smallish, as then your history will go back further. I found that most Macs seem to back up about 1-3 MB every hour, whereas mine always backed up 105-110MB. What was this mysterious file which was changing every hour that seemed to be 105MB big?
To diagnose this, I used Apple’s whizzy DTrace front-end, known as Instruments, to attach to the “backupd” process which does the time machine backups. I used some preset DTrace probes which can instrument the APIs used to read and write files, thus giving me lists of all the reads and writes, including their sizes, filenames, and even call stacks. And there’s even a nice UI to look at the results:
The mysterious 105MB file turned out to be the article database for my RSS reader. It appears that they store all the articles in one file (messages.db) instead of many small ones. So, each time it refreshes (more than once per hour) the file changes, and Time Machine chooses to back it up.
So, the solution is simple – check whether there’s a fixed version of Vienna, or move to a new RSS reader, or tell Time Machine to ignore this file.
As for Symbian, perhaps there will be something like DTrace one day! I can’t wait!
PIPS is Symbian’s newish POSIX API layer. On the whole it’s pretty good; the APIs work well, although there is not much support for “related issues” such as building using GNU autoconf, link-by-name, and interfacing with other Symbian code.
However, PIPS 1.3 doesn’t work on Motorola phones. This means a customer of mine can’t release their software for Motorola devices, and the same will apply to many others I’m sure.
So, for the record, here’s Motorola’s explanation:
“We found that PIPS 1.3 is not supported with Motorola Z8 devices as no manufacturing capabilities are supported with Z8 in order to install PIPS 1.3 Software applications.We no longer intend to support with Z8.”
“However we are evaluating to support with our future UIQ devices for PIPS 1.3 Software application installation. Hopefully we will support.”
That’s nice, then!
(In all fairness, contrary to what Motorola Developer Support say above, I’ve been told from other sources that this is a temporary situation, and PIPS should work again on all Motorola phones – including the Z8 – in due course.)
There are two interesting things about this release.
The first is that an indexer bug has been fixed to work with templated types. Symbian OS descriptors are usually templated types, and so this is a big deal. It means a lot of features now work with Symbian APIs which previously didn’t – such as the call hierarchy, F3 to open definition, etc.
Just like in previous Carbide.c++ versions, when Carbide can’t understand your code, the code is shown in grey. The difference is that in previous Carbide builds it was probably a Carbide bug, whereas now it’s 99% likely to be a bug in your code. Several times now I’ve thought to myself, “oh, that code looks fine, Carbide must be imagining it” and sure enough, the indexer is right, I’ve messed something up.
For those reasons alone I wholeheartedly recommend joining the Carbide.c++ 2.0 beta and using the new version.
The second thing is the presence of a new perspective in Carbide.c++ – a Qt perspective. A few months ago, you might have noticed Nokia bought Trolltech, the makers of Qt. At the time there was speculation about what Nokia would do. Would they port Qt on top of S60? Would they replace S60? Would they start to make Linux/QT phones?
Well, the first answers are beginning to appear in this version of Carbide.c++. For example, the Qt perspective has editors for Qt actions, properties, objects, slots and widgets. That seems a lot to me, and although these views appear to belong to a com.trolltech.qtcppdesigner package and therefore aren’t produced by the Carbide.c++ team, it looks like a lot of the effort in Carbide.c++ 2.0 has gone into Qt work as well as Symbian work. I may be wrong!
Also, the Qt perspective doesn’t show the Symbian Project Navigator view. There’s nothing in that view which is specific to Symbian UIs – it’s all about the Symbian build system. That suggests to me that whatever Qt stuff is going to be happening in Carbide.c++ 2.0, it will not involve the Symbian build system, which in turn means it’s based on Linux (or something) rather than Symbian.
Again, I may be wrong, but that’s my prediction. It looks to me like Carbide.c++ is going to turn into a dual-purpose tool: Qt/Linux as well as S60/Symbian, rather than Qt-on-Symbian. It will be interesting to find out if I’m completely off the mark.
(Incidentally, this leads onto another vague interest of mine – getting the cross-platform make system cmake to generate Symbian OS MMP and bld.inf files. I vaguely plan to investigate that one day, but haven’t yet. I believe that KDE uses cmake, which suggests it’s popular in the Qt world. If there is any crossover, perhaps that’s been done somewhere already.)
This clears up a few bugs, displays the conditions more nicely, and makes things quicker. Use Carbide’s built-in software update to fetch the new version.
A customer has given me a contract to deploy my tools on their codebase, to see whether they come up with useful results. After that, maybe they’ll talk about licencing the tool… very exciting! But of course I’ve failed to fix all the things I had wanted to fix in the time leading up to this demonstration, so I know it won’t meet their criteria, quite. Sugar!