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12.2 Rebuilding Debug Info

As we saw above, some packages, but not all, provide debugging info in a debug output. What can you do when debugging info is missing? The --with-debug-info option provides a solution to that: it allows you to rebuild the package(s) for which debugging info is missing—and only those—and to graft those onto the application you’re debugging. Thus, while it’s not as fast as installing a debug output, it is relatively inexpensive.

Let’s illustrate that. Suppose you’re experiencing a bug in Inkscape and would like to see what’s going on in GLib, a library that’s deep down in its dependency graph. As it turns out, GLib does not have a debug output and the backtrace GDB shows is all sadness:

(gdb) bt
#0  0x00007ffff5f92190 in g_getenv ()
   from /gnu/store/…-glib-2.62.6/lib/
#1  0x00007ffff608a7d6 in gobject_init_ctor ()
   from /gnu/store/…-glib-2.62.6/lib/
#2  0x00007ffff7fe275a in call_init (l=<optimized out>, argc=argc@entry=1, argv=argv@entry=0x7fffffffcfd8, 
    env=env@entry=0x7fffffffcfe8) at dl-init.c:72
#3  0x00007ffff7fe2866 in call_init (env=0x7fffffffcfe8, argv=0x7fffffffcfd8, argc=1, l=<optimized out>)
    at dl-init.c:118

To address that, you install Inkscape linked against a variant GLib that contains debug info:

guix install inkscape --with-debug-info=glib

This time, debugging will be a whole lot nicer:

$ gdb --args sh -c 'exec inkscape'
(gdb) b g_getenv
Function "g_getenv" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (g_getenv) pending.
(gdb) r
Starting program: /gnu/store/…-profile/bin/sh -c exec\ inkscape
(gdb) bt
#0  g_getenv (variable=variable@entry=0x7ffff60c7a2e "GOBJECT_DEBUG") at ../glib-2.62.6/glib/genviron.c:252
#1  0x00007ffff608a7d6 in gobject_init () at ../glib-2.62.6/gobject/gtype.c:4380
#2  gobject_init_ctor () at ../glib-2.62.6/gobject/gtype.c:4493
#3  0x00007ffff7fe275a in call_init (l=<optimized out>, argc=argc@entry=3, argv=argv@entry=0x7fffffffd088, 
    env=env@entry=0x7fffffffd0a8) at dl-init.c:72

Much better!

Note that there can be packages for which --with-debug-info will not have the desired effect. See --with-debug-info, for more information.

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