Frysk and selective coredumps

Been working hard on Frysk over the last year, and hardware watch points are coming along quite nicely. I stopped back in core file land again recently, to update some code and add a few features. There was a bit of discussion some months ago on creating partial or selective user-land core dumps. As a core dump can be very large (especially if the process’s heap is large) then the resulting file construction can be time consuming. So added a feature to fcore (the Frysk core dump command line utility) to allow selective segment inclusion and exclusion.

So for example:

sleep 100 &

[1] 7480

fcore -o partialcore -segments=”stack|heap|vdso|($^)” 7480

Will dump the segments that match the program’s: stack, heap, its virtual dynamic shared object (vdso) and any maps without a name (maps not backed with a file). As core files are sparse, we have to use the -s option is ls to look at the size difference:

X86_64, Fedora 8

frysk-core/frysk/bindir/fcore -o partialcore -segments=”stack|heap|vdso|($^)” 7480
frysk-core/frysk/bindir/fcore -o fullcore -allmaps 7480
frysk-core/frysk/bindir/fcore -o normalcore 7480

ls -lash partialcore.7480 fullcore.7480 normalcore.7480
77M -rw-r–r– 1 test test 77M 2008-02-29 10:01 fullcore.7480
75M -rw-r–r– 1 test test 77M 2008-02-29 10:02 normalcore.7480
312K -rw-r–r– 1 test test 77M 2008-02-29 10:01 partialcore.7480

These are small examples, but I’d like to see if this feature is useful to people. If it proves to be so, it can expanded to other criteria beyond the map name. Right now this exists in Frysk’s GIT repository which can be cloned at:

git clone ssh://

And you can reach us on irc at: #frysk, at

It should find its way into the frysk rpm in Fedora 8 very soon.

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