Re: [gentoo-dev] Re: debug/release builds extensions/clarification proposal

[Maciej Mrozowski]

On Monday 01 of December 2008 09:36:12 Diego 'Flameeyes' Pettenò wrote:
> > - USE=debug is useless  when CFLAGS/LDFLAGS or FEATURES are not
> > appropriate
> What are you saying here? I'm afraid you're mistaken here.

The point is to look at this from users' (well, a bit) point of view - 
USE=debug variable is ambiguous in it's meaning. While it enables only 
codepaths (asserts, #ifdefs and similar) it suggests (by name and for some 
packages not only suggests) enabling debug symbols.
And policy is to enforce CFLAGS from make.conf and wipe out every package-
defined flags as far as I know.

> For the most part, USE=debug means "enable debug code paths", which for
> lots of projects simply means "enable assertions"; there are packages
> that take this as "enable debug symbols too" but I don't think that's
> very valid since users might want debug code paths but not symbols and
> vice-versa (I indeed have debug symbols bug no debug codepaths enabled).

That's correct, the problem is - Gentoo does not provide officially supported 
mechanism of enabling both or just debug symbols per package basis - it 
doesn't even provide any supported/documented mechanism for per package 
CFLAGS, FEATURES and similar.
If /etc/portage/env hack/feature could be made official (for CFLAGS,LDFLAGS 
and bash-domain FEATURES) - it could address this issue good enough, because 
with proper smart combination of symlinks/files the "ultimate configuration" 
power would be delivered, not just "cleaning/workaround" I am actually 
proposing. Per package debug/release/profile/or_any_other configuration is 
what I would pursue, and in my proposal I used USE=debug as existing and 
supported way of achieving this.

While I don't like hack @pve uses (I prefer portage/env as more convenient 
way), his idea about emerge --info <pkg> seems interesting.

> - -ggdb *does not have any runtime performance hit*; neither in

Yes, I'm well aware of that, though it increases disk space requirements a bit 
as it's applied to all libs/bins.

> - -O0 is not always a good idea; beside bugs in packages concealed by
>    -O1+ [1]

[1] is a pathology and should be fought against, -O1+ may leave frame stack 
useless for debugging due to inline optimizations in some places (especially 
debugging inline class implementations is limited, which affects Qt/KDE) - 
besides - I may not stated it clear - those default values would be defined in 
the very same make.conf, so it could be:

CHOST="x86_64-pc-linux-gnu"                                                  
CFLAGS="-march=nocona -O2 -pipe -msse3 -ftree-vectorize"
CXXFLAGS="${CFLAGS}"

CFLAGS_DEBUG="-O2 -ggdb"

Yet, I still cannot think of this proposal other way like of dirty workaround 
for the problem, that doesn't really exist (well, at least for developers, who 
have meta-distribution and ultimate freedom for user in mind).  For the users 
the problem is real, of course it's usually a consequence of either not being 
aware of those mechanisms or as a result of ambiguous semantics of USE=debug.

And what about pushing some bash-domain FEATURES to USE flags? Like nostrip, 
splitdebug? I guess being able to set it per package is important.

-- 
regards
MM