Review Request 119498: Report crashes of KDE apps in Apple OS X (2) (fix drkonqi)

[Ian Wadham]

> On July 27, 2014, 11:17 a.m., Thomas Lübking wrote:
> > drkonqi/gdbhighlighter.cpp, line 74
> > <https://git.reviewboard.kde.org/r/119498/diff/1/?file=293510#file293510line74>
> >
> >     an abort is not a crash ;-)
> >     
> >     If you hit this assert, the looked up (lineNr - 1) is somehow out of bounds, ie. there's no line with a key >= (lineNr -1) in the map.
> >     
> >     This should likely never happen on any system.
> >     Can you check what the lineNr actually is as compared to
> >     
> >        qDebug() << lineNr << lines.keys();
> >        
> >     ?
> 
> Ian Wadham wrote:
>     I did at one time have a few qDebug() statements to try and find what was wrong with the algorithm. AFAICT it is trying to match one or more lines in (const QString& text) with single (possibly long) lines of backtrace in QMap<int, BacktraceLine>. I think it failed if one backtrace line was formatted into three text lines or maybe if the last backtrace line was formatted into two text lines. AFAICT (there is a real dearth of explanatory comments) the code is merely introducing pretty colours, etc. into the formatted text. As such, it should not abort Dr Konqi and lose the crash report.
> 
> Thomas Lübking wrote:
>     Of course it should not crash.
>     
>     The point is that the assert explicitly tells you that there's something wrong with the code.
>     Skippping it won't fix the issu - that's like puting duct tape over a warning sign on your cars dashboard to fix "no cooling water".
>     
>     
>     Since the lines map seems only used to map lines to textblocks, i assume the issue is that the lines are eg. not "\n" terminated in gdb output on OSX (no idea, though) and the only item in the map is that for the key "0"
>     
>     In this case that'd be the issue to fix.

Please spare me the motoring analogies. To me, the ASSERT at this point, is like bringing the car to a screeching halt or running it into the nearest fence, simply because the glovebox light will not come on. I am a real-time and O/S programmer from way back and have designed and written a few crash procedures for different systems. They need to be rugged and simple (unlike Dr Konqi IMHO) and to succeed no matter what. This used to be called failsafe programming, graceful failure or graceful degradation. If an ASSERT and abort technique has to be used in RT programming, to prevent potential database corruption, it needs to be backed by an appropriate recovery and restart procedure.

Actually I think lines.end() is a legitimate return from lines.lowerBound(lineNr - 1) in Dr K's algorithm (see http://qt-project.org/doc/qt-5/qmap.html#lowerBound coding examples). The lineNr can actually get ahead of the number of lines in the map by by too much, if there are several multi-line entries in QString& text. Using an ASSERT looks like lazy programming to me (Thinks: "I cannot see what to do in this case, so I'll put in an ASSERT and see if it actually happens in practice." ???). My solution is to re-use the last entry from the QMap. Another might be to use "return;" instead of the ASSERT, leaving the last bit of the highlighting incomplete, but not losing the valuable backtrace data.

A better (more rugged) approach might be:

    get a line from "text"
    if it is from the left-hand end of a backtrace entry (i.e. not a continuation line)
        get the next backtrace entry
        if past last entry
            return
    re-format the line from "text"

I would have used something like that in my patch, but I do not know enough about the format of backtrace data to get the first "if" condition right. How would I?

Re "\n" characters, they occur as expected in the content of "QString& text" on Apple OS X.


- Ian


-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://git.reviewboard.kde.org/r/119498/#review63254
-----------------------------------------------------------


On July 27, 2014, 9:16 a.m., Ian Wadham wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/119498/
> -----------------------------------------------------------
> 
> (Updated July 27, 2014, 9:16 a.m.)
> 
> 
> Review request for KDE Software on Mac OS X, KDE Runtime, kdelibs, and Michael Pyne.
> 
> 
> Repository: kde-runtime
> 
> 
> Description
> -------
> 
> When a KDE app crashes in Apple OS X, it just disappears from the screen. At the most, the user is invited to report the crash to Apple. AFAIK this has been a problem in KDE on Apple OS X for years, leading to frustration with KDE among Apple users and MacPorts developers and an attitude among KDE developers of "Why does nobody report the problem(s) on bugs.kde.org?"
> 
> It is my strong belief that the failure to report crashes of KDE apps in Apple OS X also exists in Frameworks.
> 
> So far I have identified a number of portability bugs in KDE on Apple OS X: 1 in KCrash, 1 in kdeinit4 and 5 in Dr Konqi. Three patches for Dr Konqi are submitted in this review. Patches for KCrash and kdeinit4 are submitted in part 1 of this review, against kdelibs. I am still investigating the other two problems in Dr Konqi - and there could be more than two...
> 
> In this review we have three portability problems:
> 
> 1. On Apple OS X, Dr Konqi's dialog box hides itself underneath the main window of the app that has just crashed, so is effectively useless. This appears to be because Dr Konqi is started by a Linux/Unix method (fork() + exec()?). If an app is started with the Apple OS X "open" command, it always appears on top. The patch just raises the dialog box.
> 
> 2. When formatting the backtrace output, Dr Konqi crashes (with an ASSERT) on the last line. This appears to be an error in the algorithm used (i.e. also a bug in Linux KDE), but the patch is treating it as an Apple OS X portability problem for now.
> 
> 3. Dr Konqi checks whether the user can save cookies in kcookiejar and, if not, stops reporting the crash. On Apple OS X, cookies would be kept in another browser (e.g. Safari or Firefox) and not in KDE's default browser (Konqueror) and cookie jar. IMHO, Dr K should report the crash no matter what, as long as it can connect to bugs.kde.org and log in.
> 
> 
> Diffs
> -----
> 
>   drkonqi/reportassistantpages_bugzilla.cpp 86ca327 
>   drkonqi/gdbhighlighter.cpp 7cd0aa9 
>   drkonqi/main.cpp 75e060e 
> 
> Diff: https://git.reviewboard.kde.org/r/119498/diff/
> 
> 
> Testing
> -------
> 
> Using Apple OS X 10.7.5 (Lion) on a MacBook Pro, I have installed KDE libs via MacPorts (at version 4.12.5) and I have adapted kdesrc-build to run in an Apple OS X environment and used it to test against the KDE 4.13 branch. I have been testing with a KDE app that I can crash at will and using stderr and Apple OS X Console log output to determine the outcome.
> 
> Please note that I am the -only- KDE developer who has this kind of setup, but I am NOT a KDE core developer. My experience before now has been in KDE Games. However I used to be a UNIX and database guru before I retired in 1998.
> 
> I NEED HELP from KDE -core- developers to proceed further. These problems will also exist in Dr Konqi for KF 5, but I am as yet unable to build or test Frameworks on Apple OS X and I cannot find Dr Konqi among the Frameworks repositories. I am sure there are many more Apple OS X portability problems in Dr Konqi and other KDE software.
> 
> Without my patches, Dr Konqi, on Apple OS X, remains invisible to the user, often fails to complete the backtrace report and then fails to connect to bugs.kde.org.
> 
> With my patches, Dr Konqi on Apple OS X can generate a full crash report, including the backtrace and the results of the dialog with the user. Sometimes, however, it fails to submit the completed report to bugs.kde.org. This problem is still under investigation.
> 
> I would not have got this far without help from Michael Pyne, Thomas Lübking and several of the MacPorts developers, as well as the unfailing enthusiasm and encouragement of my friend Marko Käning.
> 
> 
> Thanks,
> 
> Ian Wadham
> 
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.kde.org/pipermail/kde-core-devel/attachments/20140730/79a8a07b/attachment.htm>