debug libraries

[Giorgos Keramidas]

On Thu, 25 Feb 2010 11:09:36 -0800 (PST), "Dr. Baud" <drbaud at yahoo.com> wrote:
> Apologies if this is the wrong list....
>
> Are there prepackaged debug versions of the system libraries available
> (like 'yum install *-debuginfo' in Fedora and 'apt-get install *-dbg'
> in Ubuntu)?

No, not really.  You can always build a base system *with* debugging
symbols from source though.  Naturally, this is not as fast to install
as a small set of pre-built packages, but it is at least possible.

For example, my laptop runs a base system _with_ debugging symbols most
of the time.  To rebuild everything I made the following changes to my
'/etc/make.conf' file:

  1. I enabled the DEBUG_FLAGS option, by adding the following:

         DEBUG_FLAGS ?= -g

  2. I checked that I am not using high optimization levels in CFLAGS or
     COPTFLAGS.

  3. I enabled the NO_CPU_CFLAGS and NO_CPU_COPTFLAGS options:

         NO_CPU_CFLAGS=         # Don't add -march=<cpu> to CFLAGS automatically
         NO_CPU_COPTFLAGS=      # Don't add -march=<cpu> to COPTFLAGS automatically

Then I rebuilt everything from my latest source tree at /usr/src.

The combined effect of NO_CPU_CFLAGS and DEBUG_FLAGS is that binaries
are not stripped before they are installed, and optimization flags are
not added automatically by the build system.

Note #1.  The resulting binaries are *much* larger.  For example the
ed(1) editor in unstripped format is 123 KB on my laptop, but stripping
it reduces its size down to 48 KB:

    keramida at kobe:/tmp$ ls -ld /bin/ed
    -r-xr-xr-x  2 root      wheel  - 123663 16 Φεβ 12:25 /bin/ed
    keramida at kobe:/tmp$ cp -a /bin/ed ed
    keramida at kobe:/tmp$ sudo strip -s ed
    keramida at kobe:/tmp$ ls -ld ed
    -r-xr-xr-x  1 keramida  wheel  - 48400 26 Φεβ 17:24 ed

The effect of enabling debugging flags for larger programs like gcc, gdb
or bind is much much larger than ed(1) of course.

Note #2.  There's probably a measurable performance hit by running a
debugging base system, because -O2 optimizations do not get a chance to
do their magic as you build your binaries.

HTH,
Giorgos