Bug#71781: [Bug-hurd] Bug#71781: [hurd] dh_compress causes kernel panic

[Roland McGrath]

That looks like a null pointer access, or rather a structure (or array)
access to 8 bytes off a pointer that turns out to be null.

The thing to do is run gdb on your gnumach binary (on linux is fine) and
say "info line *PC" where PC is the eip value quoted there.  That will show
you the source location (in M-x gdb mode in emacs, that just pops the
source right up in an emacs buffer), and you can show us where it is.
There is some way to get the same information using objdump, but I find gdb
the easiest way to find the source location quickly.

If you use oskit-mach and this happens there, you can use gdb over a serial
line from another computer to debug kernel traps in style.