Re: [Qemu-devel] Should configure --enable-debug add -Og to CFLAGS?

[Daniel P . Berrangé]

On Thu, Jun 27, 2019 at 05:43:30PM +0200, Markus Armbruster wrote:
> The fine manual advises:
> 
> '-O0'
>      Reduce compilation time and make debugging produce the expected
>      results.  This is the default.
> [...]
> '-Og'
>      Optimize debugging experience.  '-Og' should be the optimization
>      level of choice for the standard edit-compile-debug cycle, offering
>      a reasonable level of optimization while maintaining fast
>      compilation and a good debugging experience.  It is a better choice
>      than '-O0' for producing debuggable code because some compiler
>      passes that collect debug information are disabled at '-O0'.
> 
> Our configure --enable-debug effectively picks -O0.  Should it pick -Og
> instead?

NB, it is the --enable-debug-info option to configure that actually
adds the "-g" flag for debug info in objects, and turns off -O2.

--enable-debug turns on TCG and Mutex debugging & disables fortify
source, but doesn't affect optimization level.

Adding -Og to --enable-debug-info would be problematic for Fedora/RHEL
distro builds, as we want debugging symbols, but also still want -O2
to be used.

Yes, the naming of these options is a trapdoor over a pit of crocodiles :-)

Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|