[Libreoffice] Even more debugging info

[Stephan Bergmann]

On 11/30/2011 09:34 PM, Tom Tromey wrote:
>>>>>> "Stephan" == Stephan Bergmann<sbergman at redhat.com>  writes:
> 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.

I think we need some sensible default for LO here, one that is useful 
but does not cause problems for the inexperienced (e.g., some of LO's 
libs already stress the linker quite heavily; would be bad if changing 
something would turn this from "quite heavily" to "so immensely it 
starts to break a low-powered system," say).

> 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.
>
> 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.

Ah, good to know.  Things we should investigate.

Thanks,
Stephan