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Say you want to try running file system server ([[`ext2fs`|translator/ext2fs]],
[[`jfs`|translator/jfs]], ...) against a modified version of
[[`libpager`|libpager]] and debug the latter one using [[debugging/GDB]].

On Debian you need the `hurd-dbgsym` and `libc0.3-dbg` packages installed.

Set the [[hurd/translator]] like this:

    $ settrans -fgap ↩
      jfs.img.i ↩
      /usr/bin/env ↩
        LD_LIBRARY_PATH=~tschwinge/tmp/hurd/hurd.ogi/build/libpager ↩
      "$PWD"/jfs.obj/jfs ↩
        "$PWD"/jfs.img

Then, when starting GDB, start it like this (or use an equivalent method, of
course):

    $ LD_LIBRARY_PATH=~tschwinge/tmp/hurd/hurd.ogi/build/libpager ↩
      gdb ↩
        ~tschwinge/tmp/jfs/jfs.obj/jfs 15436
    GNU gdb 6.5-debian
    [...]
    Reading symbols from /lib/libdiskfs.so.0.3...Reading symbols from /lib/debug/lib/libdiskfs.so.0.3...done.
    done.
    Loaded symbols for /lib/libdiskfs.so.0.3
    Reading symbols from /devel4/tschwinge/tmp/hurd/hurd.ogi/build/libpager/libpager.so.0.3...done.
    Loaded symbols for /devel4/tschwinge/tmp/hurd/hurd.ogi/build/libpager/libpager.so.0.3
    Reading symbols from /lib/libstore.so.0.3...Reading symbols from /lib/debug/lib/libstore.so.0.3...done.
    done.
    Loaded symbols for /lib/libstore.so.0.3
    [...]
    (gdb) break pager_demuxer
    Breakpoint 1 at 0x105c98d: file ../../libpager/demuxer.c, line 27.
    [...]
    Breakpoint 1, pager_demuxer (inp=0x12bded0, outp=0x12bbec0) at ../../libpager/demuxer.c:27
    27      {
    (gdb) list
    22      /* Demultiplex a single message directed at a pager port; INP is the
    23         message received; fill OUTP with the reply.  */
    24      int
    25      pager_demuxer (mach_msg_header_t *inp,
    [...]

Voilà.

If you need to debug the initialization of the translator, start the translator
like

    $ settrans -Pa /foo /hurd/foofs

The `-P` option will make it
pause and you will be able to attach [[debugging/GDB]] to the process.