Strace Service Message

January 19th, 2015 by mortenw

Just a service reminder: application writers should run their applications under strace from time to time.

I just did for Gnumeric and discovered that on startup we were creating a large number of files in /tmp like this:

open("/tmp/gdkpixbuf-xpm-tmp.XAXESX", O_RDWR|O_CREAT|O_EXCL, 0600) = 9

I tracked this down to embedding icons in xpm format. The gdk-pixbuf loader for xpm is unable to load from memory so it creates a temporary file and loads from that. Ick! The solution is to fix and deploy the loader (impractical), not use xpm (possible), or to use preprocess='to-pixdata' when embedding.

Word Crimes

July 28th, 2014 by mortenw

I have just one thing to add to Weird Al’s Word Crimes video: I want a Biohazard Bin too. (At 3:02.)

How Does One Create A Gtk+ Application?

June 23rd, 2014 by mortenw

How does one go about creating a gtk+ working application? Is it even possible?


TL;DR: The Gtk+ ABI is broken so often that distribution-supplied binaries rarely work.

* * *

Imagine it is the time when Gtk+ 3.0 was released. You have a beautiful application with no bugs. For the sake of argument. Distributions ship it pre-compiled and life is good.

Then distributions update Gtk+ and everything based on GtkGrid breaks. You work around that in your source code, but distributions do not release new versions of your program until its next release.

In the meantime, Gtk+ breaks ABI compatibility for mouse wheel scrolling. Distributions update that and your program ceases to work with mouse wheels. You work around that in your source code, but distributions do not release new versions of your program until its next release.

In the meantime, Gtk+ breaks ABI compatibility of scrolled windows. Windows that used to have sane sizes now have near-zero size and when distributions update Gtk+, users of your application are not impressed. You work around that in your source code, but distributions do not release new versions of your program until its next release.

In the meantime, Gtk+ breaks ABI compatibility of redrawing. Parts of the gui that used to render correctly now stops updating at all. When distributions update Gtk+, your program ceases to work. You work around that in your source code, but distributions do not release new versions of your program until its next release.

Somewhere in the middle of this, Ubuntu decides to break scrollbars using a Gtk+ plugin. Your first hint that this has happened is when Ubuntu users start filing bug reports.

In the meantime, the layout rules for GtkGrid change again. When distributions update Gtk+, your program looks awful. You work around that in your source code, but distributions do not release new versions of your program until its next release.

Your program works with multiple screens. Or rather, it used to work with multiple screens. Then Gtk+ dropped support for it without notice.

Now I hear we are in for another round of breaking rendering because of some Wayland deficiency. It sounds like something that will require a runtime version check to deal with. In the meantime, if any distribution ships with updated Gtk+ but without your program updated, well, things will be broken.

* * *

The sum of all the above is that your application will have serious issues for anyone using the distribution supplied binary. And it is not because of anything you did wrong!

How does one shield oneself from this, i.e., how does one ensure that the binary compiled (say) three years (or months) ago continues to work reasonably? I don’t know. As far as I know, Gtk+ does not support parallel installations of 3.0, 3.2, …; if Gtk+ does support it, then none of the distributions do it. I’m sure it would be painful. Note, that using static copies of Gtk+ is not a viable solution because the binaries are created by distributions. They really have no way of knowing what Gtk+ version to use for any given application and they probably would not like to deal with the security implications of static linking.

(Note: the time ordering of the above is probably off here and there. There are probably also more ABI breaks that I do not remember right now.)

No, I am the CADT

March 29th, 2014 by mortenw

Sorry, Luis, I am the CADT. I believe you have your timing wrong.

At the time, was run out of some server Miguel had set up in Mexico. It was some buggy, early version of Debian’s bug system that rolled over and died when someone shipped binary data. I.e., all the time.

It was also low on disk space. Consequently, in order to keep it running, I wrote scripts to mass close (and therefore let expire) thousands of bugs. It was that or not having a running bug system. Owen Taylor was most unhappy about the expiration — can’t really fault him — and, I believe, brought in the current bugzilla based system served by Redhat.

There was something about screensaver bugs having jwz’s name on them that caused him to get more than his fair share of the resulting emails. I forget the details of that.

Writing Tests is Humbling

March 11th, 2014 by mortenw

I have spent some time recently writing import/export tests cases for Gnumeric. It is what you do when you see a mistake that it should not have been possible to make, in this case a hang when writing certain strings to the obsolete xls/biff7 format.

Writing these tests has been a very humbling experience. Highly recommended.

A lot of the code being subjected to tests is quite old: 10-15 years old. You would think that by now it would have had any obvious bugs beating out of it. No such luck. Not only were there ancient bugs — such as the direction of diagonal borders being flipped on load+save — but there were also bugs accidentally introduced when fixing other things.

Bugs happen, even where you think you are being careful. And that is not a problem. The problem arises when the bugs are not caught and make it into releases. This is where a brutal test suite is needed. Our test suite clearly was not evil enough for import and export of various formats, so I have been adding something I call round-trip tests for ods, xls/biff7, xls/biff8, and xlsx.

A round-trip test is a test that when we convert to a given format and back to our own Gnumeric format, nothing changes. Or, if something does change, then only parts we understand change. If the format is deficient, there is not much we can do. For example: ods cannot store patterned background or the sheet size; xlsx cannot store solver parameters; xls/biff7 cannot store arbitrary unicode; and xls/biff8 has a fixed sheet size of 64k-by-256. Note, that by itself a round-trip test does not guarantee that what we produce is correct. We could, hypothetically, have swapped division and multiplication are still gotten a perfect round-trip. To test that the generated files are correct one has to load the resulting sheet in Excel or LibreOffice (which, despite claims to the contrary, are what really defines xls/xlsx and ods formats). Unfortunately, I do not know how to script that so it is not automatic.

As a result of all the new tests, the recently released Gnumeric 1.12.12 should interact better with other spreadsheets.

Note: some of these new tests were probably a decade overdue. My excuse is that The Gnumeric Team is fairly small. I do hope that LO/OO already have an evil test suite, but I am not optimistic. I ran a few of my test sheets through LO and saw things like truncated strings.

Gcc vs. Clang for Error Messages

January 27th, 2014 by mortenw

So the gcc vs. clang debate flamed up again. I thought I would deliver my few cents too.

It is claimed from time to time that clang has more helpful error messages. It is, in my opinion, a clain that is just plain wrong. They both stink. Let’s look at a few samples:

static int foo (int a, int b) { return a + b; }
int bar (int a) { return foo (a (4 + 1) * 2); }

gcc says (excerpts):

e1.c:2:33: error: called object ‘a’ is not a function or function pointer
e1.c:2:1: error: too few arguments to function ‘foo’

clang says (excerpts):

e1.c:2:33: error: called object type 'int' is not a function or function pointer

The best thing you can say about the error messages here is that they at least point you to the right location. gcc is a tad better by virtue of printing the second error message which at least hints of the real problem, but neither compiler tell us what the problem is: “missing comma”. It looks like clang is suppressing the second and further errors on a line. Note, however, that in this case it has suppressed the more informative error.

Moving on with a missing opening parenthesis:

static int foo (int a, int b) { return a + b; }
int bar (int a) { return foo a); }

From gcc we get the wisdom

e2.c:2:19: warning: return makes integer from pointer without a cast [enabled by default]
e2.c:2:30: error: expected ‘;’ before ‘a’
e2.c:2:31: error: expected statement before ‘)’ token

while clang produces

e2.c:2:26: warning: incompatible pointer to integer conversion returning
'int (int, int)' from a function with result type 'int' [-Wint-conversion]
e2.c:2:29: error: expected ';' after return statement

I don’t see that one set of utter nonsense is better than the other and spending time colour coding the output shows a dubious set of priorities. Clang would do well to add hyphens to “pointer to integer”.

How about this?

#include <stdio.h>
#define EMIT(c) fprintf(stderr,"%c",(c))

Nothing from gcc, nothing from clang, nothing from sparse. Yet it’s a clear violation of C99’s paragraph 7.26.3.

C++ doesn’t fare any better:

#include <vector>
std::vector<int,int> foo; // should have been map

gcc delivers 67 lines of nonsense starting with

/usr/include/c++/4.8/ext/alloc_traits.h:199:53: error: ‘int’ is not a class, str
uct, or union type
typedef typename _Alloc::pointer pointer;

whereas clang emits 87 lines of garbage starting with

:199:22: error: type 'int' cannot be used prior to '::' because it has no member
typedef typename _Alloc::pointer pointer;

Again, the error messages are startingly useless in both cases. A sane error message would start with “type int is not valid for the second template argument to std::vector”.

The quality of error messages has been the subject of jokes for decades. Insofar clang is new code, it would appear that they have squandered any opportunity for making real improvements opting instead for putting lipstick on a pig.

Spreadsheets and the Command Line

January 1st, 2013 by mortenw

Spreadsheets are not the most obvious type of document to manipulate from the command line. They are essentially a visual tool meant for interactively exploring data. Experience has shown, however, that there are certain spreadsheet tasks for which the command line is very useful and Gnumeric supplies a number of command line tools for this.

  • ssconvert converts spreadsheets from one format to another, for example from xls to ods. That sounds fairly simple — load one, save the other — and it pretty much is although there are things such as merging several files or extracting parts of files that add a little complication. Since Gnumeric can save as pdf, this tool also allows command-line printing of spreadsheets.
  • ssgrep is like grep is for text files. And it has about the same set of options.
  • ssindex is used by things like tracker and beagle to find of pieces of text in spreadsheet files.
  • ssdiff is a new tool in the upcoming release. It compares two spreadsheets and outputs a list of differences between them. There are three output modes so far: (1) a text format, (2) an xml format, and (3) a mode that outputs a copy of one of the input files with differing cells marked in neon yellow.

None of these programs are big: 300-1100 lines of C code, ssdiff being the largest only because of its three output modes.

Where are the app developers?

June 26th, 2012 by mortenw

Jewelfox asks where the app developers for Gnome are.

My personal guess is that they have seen the incessant API breaks in the Gnome stack and have realized that making a Gnome application is task for Sisyphus.

For the record, the latest API break I am aware of is the Gtk+ change that broke scroll wheels.

GMail Cross-Mailbox Information Leakage

November 21st, 2011 by mortenw

GMail likes to present ads that are relevant to you by looking at the information in your mailbox. Fine. That is well known and just using the information you have chosen to store at Google.

However, when you use GMail to reply to a message sent by another GMail user, you will be shown ads based on the other user’s recent email activity.

That is news to me and outright scary.

I.e., do not use GMail to communicate to your doctor about an embarrassing disease because next time you write to your mother-in-law she will know. (Even if she always suspected.)


July 25th, 2011 by mortenw


I have been to events like the one on Utøya. Several such events. Not the exact one, but change political denomination, move a country south, and go back 15 years. Details, in other words, that the crackpot-du-jour randomly decided. For all practical purposes I could have been there.

Let the wheels of the justice system grind. Followed, one hopes, by a long, very lonely stay in a gray cell with easy access to newspapers documenting him fading into a position next to Quisling in public memory.