@@ 707,10 707,12 @@ output, whereas the GUIs are in a separate output. This allows users
who do not need the GUIs to save space.
There are several such multiple-output packages in the GNU distribution.
-Other conventional output names are @code{lib} for libraries and
-possibly header files, and @code{bin} for stand-alone programs. The
-outputs of a packages are listed in the third column of the output of
-@command{guix package --list-available} (@pxref{Invoking guix package}).
+Other conventional output names include @code{lib} for libraries and
+possibly header files, @code{bin} for stand-alone programs, and
+@code{debug} for debugging information (@pxref{Installing Debugging
+Files}). The outputs of a packages are listed in the third column of
+the output of @command{guix package --list-available} (@pxref{Invoking
+guix package}).
@node Invoking guix gc
@@ 1481,6 1483,7 @@ tools that help users exert that freedom.
@menu
* Packaging Guidelines:: What goes into the distribution.
+* Installing Debugging Files:: Feeding the debugger.
* Package Modules:: Packages from the programmer's viewpoint.
* Bootstrapping:: GNU/Linux built from scratch.
* Porting:: Targeting another platform or kernel.
@@ 1509,6 1512,64 @@ reject non-free firmware, recommendations of non-free software, and
discuss ways to deal with trademarks and patents.
+@node Installing Debugging Files
+@section Installing Debugging Files
+
+Program binaries, as produced by the GCC compilers for instance, are
+typically written in the ELF format, with a section containing
+@dfn{debugging information}. Debugging information is what allows the
+debugger, GDB, to map binary code to source code; it is required to
+debug a compiled program in good conditions.
+
+The problem with debugging information is that is takes up a fair amount
+of disk space. For example, debugging information for the GNU C Library
+weighs in at more than 60 MiB. Thus, as a user, keeping all the
+debugging info of all the installed programs is usually not an option.
+Yet, space savings should not come at the cost of an impediment to
+debugging---especially in the GNU system, which should make it easier
+for users to exert their computing freedom (@pxref{GNU Distribution}).
+
+Thankfully, the GNU Binary Utilities (Binutils) and GDB provide a
+mechanism that allows users to get the best of both worlds: debugging
+information can be stripped from the binaries and stored in separate
+files. GDB is then able to load debugging information from those files,
+when they are available (@pxref{Separate Debug Files,,, gdb, Debugging
+with GDB}).
+
+The GNU distribution takes advantage of this by storing debugging
+information in the @code{lib/debug} sub-directory of a separate package
+output unimaginatively called @code{debug} (@pxref{Packages with
+Multiple Outputs}). Users can choose to install the @code{debug} output
+of a package when they need it. For instance, the following command
+installs the debugging information for the GNU C Library and for GNU
+Guile:
+
+@example
+guix package -i glibc:debug -i guile:debug
+@end example
+
+GDB must then be told to look for debug files in the user's profile, by
+setting the @code{debug-file-directory} variable (consider setting it
+from the @file{~/.gdbinit} file, @pxref{Startup,,, gdb, Debugging with
+GDB}):
+
+@example
+(gdb) set debug-file-directory ~/.guix-profile/lib/debug
+@end example
+
+From there on, GDB will pick up debugging information from the
+@code{.debug} files under @file{~/.guix-profile/lib/debug}.
+
+@c XXX: keep me up-to-date
+The @code{debug} output mechanism in Guix is implemented by the
+@code{gnu-build-system} (@pxref{Defining Packages}). Currently, it is
+opt-in---debugging information is available only for those packages
+whose definition explicitly declares a @code{debug} output. This may be
+changed to opt-out in the future, if our build farm servers can handle
+the load. To check whether a package has a @code{debug} output, use
+@command{guix package --list-available} (@pxref{Invoking guix package}).
+
+
@node Package Modules
@section Package Modules