[Libreoffice] Even more debugging info

[Michael Stahl]

On 30/11/11 21:34, Tom Tromey wrote:
>>>>>> "Stephan" == Stephan Bergmann <sbergman at redhat.com> writes:
> 
> Stephan> On 11/30/2011 05:37 PM, Lionel Elie Mamane wrote:
>>> Any opinion about this patch? I have it in my local repo, and it helps
>>> me when running under gdb, as gdb now knows about macros!
> 
> Stephan> Would -ggdb3 excessively increase object size compared to -ggdb2?
> 
> The short answer is yes, but there is a more complicated answer.
> 
> First, one must consider the tradeoffs.  I always use -g3 when building
> gdb, because gdb uses macros fairly heavily, and because I just don't
> care about the extra space.  I prefer the convenience.  YMMV of course,
> and I don't know enough about LibreOffice to offer an opinion.

an interesting data point:
LO tree built with gcc 4.6.2 -g takes up 23G.

extrapolating from Lubos' mail that -ggdb3 takes 4 times as much space
the problem should be obvious :-/

my vague memory says without debug it's something like 8G, the
sources+repo ~2G.

> In a recent-enough GCC (I don't know if it made 4.6, but anyway I think
> it is in Fedora 16), there is a GNU extension to how macro information
> is represented.  This extension greatly reduces the size of the macro
> information.
> 
> If you really want to shrink debuginfo, use -gdwarf-4 and
> -fdebug-types-section.  The former has been in GCC for a while, I don't
> remember when the latter was added.  These options cause debuginfo for
> most big types to be shared across compilation units, a huge size win.
> This also makes gdb use less memory.

that sounds very useful, especially the "gdb using less memory" bit; i
assume it ought to start faster then as well.

still i'm not sure if it would get us to the point where -ggdb3 is
usable for the whole LO: if i understand correctly -fdebug-types-section
would only affect the size of libraries, not of objects;
for the sw module i currently have 767M of objects and 240M of libs.

> The downside of this feature is that not all tools have been upgraded to
> understand it.  gdb works fine, but the 7 dwarves, and systemtap, and I
> think valgrind, will barf.  They will all come around eventually, though
> I am not sure when.
> 
> Tom

so i guess we should wait until valgrind understands this feature too
before enabling it.

thanks for keeping us up to date,
 michael