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4.3. Reporting bugs

4.3. Reporting bugs

I tried pretty hard to make sure bzip2 is bug free, both by design and by testing. Hopefully you'll never need to read this section for real.

Nevertheless, if bzip2 dies with a segmentation fault, a bus error or an internal assertion failure, it will ask you to email me a bug report. Experience from years of feedback of bzip2 users indicates that almost all these problems can be traced to either compiler bugs or hardware problems.

  • Recompile the program with no optimisation, and see if it works. And/or try a different compiler. I heard all sorts of stories about various flavours of GNU C (and other compilers) generating bad code for bzip2, and I've run across two such examples myself.

    2.7.X versions of GNU C are known to generate bad code from time to time, at high optimisation levels. If you get problems, try using the flags -O2 -fomit-frame-pointer -fno-strength-reduce. You should specifically not use -funroll-loops.

    You may notice that the Makefile runs six tests as part of the build process. If the program passes all of these, it's a pretty good (but not 100%) indication that the compiler has done its job correctly.

  • If bzip2 crashes randomly, and the crashes are not repeatable, you may have a flaky memory subsystem. bzip2 really hammers your memory hierarchy, and if it's a bit marginal, you may get these problems. Ditto if your disk or I/O subsystem is slowly failing. Yup, this really does happen.

    Try using a different machine of the same type, and see if you can repeat the problem.

  • This isn't really a bug, but ... If bzip2 tells you your file is corrupted on decompression, and you obtained the file via FTP, there is a possibility that you forgot to tell FTP to do a binary mode transfer. That absolutely will cause the file to be non-decompressible. You'll have to transfer it again.

If you've incorporated libbzip2 into your own program and are getting problems, please, please, please, check that the parameters you are passing in calls to the library, are correct, and in accordance with what the documentation says is allowable. I have tried to make the library robust against such problems, but I'm sure I haven't succeeded.

Finally, if the above comments don't help, you'll have to send me a bug report. Now, it's just amazing how many people will send me a bug report saying something like:

bzip2 crashed with segmentation fault on my machine

and absolutely nothing else. Needless to say, a such a report is totally, utterly, completely and comprehensively 100% useless; a waste of your time, my time, and net bandwidth. With no details at all, there's no way I can possibly begin to figure out what the problem is.

The rules of the game are: facts, facts, facts. Don't omit them because "oh, they won't be relevant". At the bare minimum:

Machine type.  Operating system version.  
Exact version of bzip2 (do bzip2 -V).  
Exact version of the compiler used.  
Flags passed to the compiler.

However, the most important single thing that will help me is the file that you were trying to compress or decompress at the time the problem happened. Without that, my ability to do anything more than speculate about the cause, is limited.

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