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s003apr
Apprentice
Joined: 04 Oct 2002
Posts: 162
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 Posted: Wed Jan 15, 2003 2:32 pm Post subject: Emerge and Cflags - general question |
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I'm pretty much a newbie when it comes to compiling and programming so if you answer my question, it's ok to talk to me like I'm stupid, because I really am in this area.
BACKGROUND
I've only recently realized that the CFLAGS are the options we are giving gcc for compiling c code and C++FLAGS are for compiling C++ (correct?).
Since I went with a stage 3 gentoo install, I have the default flags for my athlon-xp in make.conf
| Code: | CFLAGS='-march=athlon-xp -mcpu=athlon-xp -O3 -pipe'
CXXFLAGS='-march=athlon-xp -mcpu=athlon-xp -O3 -pipe' |
I also checked make.defaults and make.globals and there was no additional options in them.
However, when I emerged something I noticed that it says the following on screen:
| Code: | | ... -I/usr/X11R6/include -DI386_ASSEM -I../../intl -march=athlon-xp -mcpu=athlon-xp -O3 -pipe -Wall -Wpointer-arith -finline-functions -ffast-math -fomit-frame-pointer -funroll-all-loops -c configure.c -fPIC |
This is of course only a small portion of all the output when building a program. From my newbie standpoint, I'd gather that this is where the file configure.c is being built.
The important thing I notice is that there are a lot of other options here that were never in my CFLAGS
ie. | Code: | | -Wall -Wpointer-arith -finline-functions -ffast-math -fomit-frame-pointer -funroll-all-loops |
QUESTION
why is it compiling with these options if I never specified these in the CFLAGS?[/code] |
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pilla
Bodhisattva
Joined: 07 Aug 2002
Posts: 7729
Location: Underworld
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| Posted: Wed Jan 15, 2003 4:38 pm Post subject: |
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Because the package can add or subtract options if it thinks it will help performance or stability in some way.
For example, some packages rollback from O3 to O2 because they are known to be broken if compiled with O3. Other packages add flags that developers think will boost performance.
I am not a developer myself, but it is this AFAIK.
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Portage & Programming
